Patent Application
20130189280
This application and any patent granted thereon is associated with and claims priority from Australian Provisional Patent Application No. 2010900571, filed on 12 Feb. 2010, entitled “Protein domains and uses therefor” and Australian Provisional Patent Application No. 2010900887, filed on 23 Feb. 2010, entitled “Protein domains and uses therefor-II”, the entire contents of which, are incorporated herein by reference.
The present disclosure relates generally to a structure-modeling approach to identify therapeutic and diagnostic targets on proteins. Means are provided to generate agents which bind and optionally antagonize a particular domain within a protein referred to as a Cleaved_Adhesin Family Domain. In an embodiment, the disclosure is directed to the control of Porphyromonas gingivalis infection or infection by related microorganisms by targeting selected domains on protease-like molecules having a hemagglutinin region. In another embodiment, the present disclosure enables the modulation or detection of a protein having a Cleaved_Adhesin domain homologous to those in the protease-like molecules.
Bibliographic details of the publications referred to by author in this specification are collected alphabetically at the end of the description.
Reference to any prior art in this specification is not, and should not be taken as, an acknowledgment or any form of suggestion that this prior art forms part of the common general knowledge in any country.
Porphyromonas gingivalis is a Gram-negative anaerobic bacterium implicated as a key pathogen in chronic periodontitis, a destructive inflammatory disease of the tissues supporting the dentition (Holt et al., Science 239:55-57, 1988, Socransky et al., J Clin Periodontol 25:134-144, 1998). Porphyromonas gingivalis is deficient in critical gene products necessary for the synthesis of the porphyrin macrocycle of heme (Roper et al., J Biol Chem 275:40316-40323 2000). As a porphyrin auxotroph, the organism must acquire this nutrient from host sources, most apparently as heme, with erythrocytes providing the major potential source. Accordingly, P. gingivalis has mechanisms for attachment and agglutination of erythrocytes, lysis of erythrocytes, capture and degradation of released hemoglobin and subsequent sequestration of heme (Lamont and Jenkinson, Microbiol Mol Biol Rev 62:1244-1263, 1998).
The virulence mechanisms of this pathogen are not fully understood but a group of cysteine proteases, the gingipains, are known to play important roles in hemagglutination, hemolysis and subsequent capture of essential heme (Pike et al., J Bacteriol 178:2876-2882, 1996, Lewis et al., J Bacteriol 181:4905-4913, 1999, Paramaesvaran et al., J Bacteriol 185:2528-2537, 2003). The lysine-specific cysteine protease (Kgp) and arginine-specific proteases A and B (RgpA and RgpB) are gingipains located on the surface of P. gingivalis or in some strains are released (Potempa et al., Infect Immun 63:1176-1182, 1995). Kgp and RgpA are encoded by single loci, kgp and rgpA, respectively, with the encoded proteins consisting of both a catalytic domain and hemagglutinin/adhesin (HA) domains (Pavloff et al., J Biol Chem 272:1595-1600, 1997, Pavloff et al., J Biol Chem 270:1007-1010, 1995, Curtis et al., J Periodontal Res 34:464-472, 1999). However, when extracted from P. gingivalis they are observed to be proteolytically processed while remaining bound in tight molecular complexes. These observations have been widely interpreted to indicate a precise physiological processing of surface gingipains. However, if prior to the extraction from the cell surface, the proteolytic activities of the gingipains are specifically inhibited, then the processing of the extracted products is incomplete. This is observed when using a monoclonal antibody to an adhesin domain epitope common to both RgpA and Kgp which detects a range of higher molecular weight fragments in extracts from pre-inhibited cells (Shi et al., J Biol Chem 274:17955-17960, 1999). This is interpreted to indicate that processing of expressed gingipain is either a continuous process during growth of the organism or that at least part of the autolytic/proteolytic processing results from the extraction process.
Of the four putative HA domains isolated from processed high molecular weight gingipains by SDS-PAGE, Rgp44/Kgp39 has been found to possess hemagglutination activity (Pike et al., J Biol Chem 269:406-411, 1994) while Kgp15/Rgp15 has been proposed to be a hemoglobin (Nakayama et al., Mol Microbiol 27:51-61, 1998) and heme binding receptor (DeCarlo et al., J Bacteriol 181:3784-3791, 1999). Rgp and Kgp have been reported to have hemoglobinase activity and the catalytic activity of Kgp is critical in this function (Shi et al., 1999 supra; Lewis et al., 1999 supra). Mutants defective in Kgp have markedly reduced capacity to sequester heme and are relatively avirulent in animal models (Shi et al., 1999 supra; Lewis et al., 1999 supra; Lewis and Macrina, Infect and Immun 66:4905-4913, 1998). Hemolytic activity of P. gingivalis has been attributed to protease action based on inhibitor profiles (Chu et al., Infect Immun 59:1932-1940, 1991). Kgp deletion mutants have approximately 50% of the hemolytic activity of mutants complemented for Kgp indicating a major contribution by this proteinase (Lewis et al., 1999 supra). The exact role of the Kgp-HA domains remains to be determined.
For the gingipains, only the crystal structure of RgpB, which contains a heavily truncated HA domain, has been determined (Eichinger et al., Embo J 18:5453-5462, 1999) and to date, the proposed structures of the HA domains have been mainly speculative. The widely accepted domain structural model of RgpA and Kgp (
There is a need to more accurately define functional domains within particular proteins in order to design highly specific interacting molecules such as for use as antagonists, agonists or diagnostic agents.
Porphyromonas gingivalis is an obligately anaerobic bacterium recognized as an etiologic agent of adult periodontis in mammals, such as humans. This microorganism produces a range of protease-like molecules including gingipains (gp) and hemagglutinin (HA) proteins (Hag proteins) such as hemagglutininA (HagA) which are involved in hemolysis of erythrocytes and heme acquisition. Porphyromonas gingivalis is a porphyrin auxotroph, requiring this molecule to grow and persist in a host. The HA region of these protease-like molecules provides a potential therapeutic target to inhibit P. gingivalis from capturing heme and, therefore, to inhibit its growth. However, the previously suggested domains have not adequately explained function and, hence, have likely not been correctly determined.
In accordance with the present disclosure, a structure-modeling approach is used to identify particular domains on protease-like molecules produced by P. gingivalis. In an embodiment, the HA region of the protease-like molecules have been subject to domain modeling based on homology to Cleaved_Adhesin Domain Family proteins (see the Cleaved_Adhesin Family PF07675 in the PFam protein families database [Finn et al., Nucleic Acids, Res 36:D281-288, 2008]). The identified domains within the HA region are referred to herein as “Cleaved_Adhesin domains”. On the lysine gingipain (Kgp) from P. gingivalis, the domains are specifically designated K1, K2 and K3. The crystal structures of K2 and K3 domains from the W83 strain of P. gingivalis have further been determined together with a model for K1. The present disclosure extends, however, to homologs or functionally or structurally equivalent domains on the arginine gingipain (Rgp), and particularly R1 and R2, and on HagA (A1 through A10) [see
Accordingly, the instant disclosure contemplates a method for the prophylaxis or treatment of infection by a microorganism in a biological environment from where the microorganism acquires iron, heme or porphyrin, the method comprising administering to the environment an effective amount of an agent for a time and under conditions sufficient to antagonize a Cleaved_Adhesin domain within the adhesin and/or carbohydrate binding region of a protease-like molecule produced by the microorganism, the domain associated with hemolysis or hemolytic activity of erythrocytes.
A method is also provided for the prophylaxis or treatment of infection by a microorganism in a mammal from where the microorganism acquires iron, heme or porphyrin, the method comprising administering to the environment an effective amount of an agent for a time and under conditions sufficient to antagonize a Cleaved_Adhesin domain within an HA region of a molecule produced by the microorganism wherein the molecule is a protease-like molecule associated with hemolysis or hemolytic activity of erythrocytes.
Also contemplated is a method for the prophylaxis or treatment of infection by Porphyromonas gingivalis or a related organism in a mammal, the method comprising administering to the mammal an effective amount of an agent for a time and under conditions sufficient to antagonize a Cleaved_Adhesin domain within the HA region of a gingipain or HagA, wherein the antagonism prevents or reduces hemolysis or hemolytic activity of erythrocytes.
The present disclosure further provides a method for prophylaxis or treatment of periodontal, pulmonary, vaginal, urethral or hoof disease resulting from infection by P. gingivalis or related microorganism in a mammal, the method comprising administering to the mammal an effective amount of an agent for a time and under conditions sufficient to antagonize a Cleaved_Adhesin domain within the HA region of a gingipain or HagA, wherein the antagonism prevents or reduces hemolysis or hemolytic activity of erythrocytes.
In an embodiment, a method is provided for the prophylaxis or treatment of infection by a microorganism in a biological environment from where the microorganism acquires iron, heme or porphyrin, the method comprising administering to the environment an effective amount of an agent for a time and under conditions sufficient to antagonize a Cleaved_Adhesin domain within an adhesin and/or carbohydrate binding region of a molecule produced by the microorganism, the domain associated with hemolysis or hemolytic activity of erythrocytes, wherein the domain is defined by Cleaved_Adhesin domain modeling.
Another aspect of the present disclosure provides a method for the treatment or prophylaxis of infection by Porphyromonas gingivalis or a related microorganism in a mammal, the method comprising administering to the mammal an antagonizing effective amount of an agent which antagonizes function of one or more of Cleaved_Adhesin domains K1, K2 and/or K3 on Kgp and/or R1 and/or R2 on Rgp and/or equivalents on HagA including one or more of A1 through A10.
As indicated above, the identification of the Cleaved_Adhesin domains enables identification of similar domains in a range of proteins from organisms not necessarily related to P. gingivalis or from un-related proteins.
Accordingly, a method is provided for identifying a protein or part thereof which comprises a Cleaved_Adhesin domain, the method comprising subjecting amino acid sequences of proteins to Cleaved_Adhesin domain modeling based on the amino acid sequences of one or more of K1, K2, K3, R1, R2 and/or A1 through A10 and selecting amino acid sequences having homology thereto wherein such identified amino acid sequences are regarded as defining a Cleaved_Adhesin domain.
The present disclosure enables the identification of potential modulators of proteins having a Cleaved_Adhesin domain homologous to or comprising a domain selected from K1, K2, K3, R1, R2 and one or more of A1 through A10. In relation to a modulator of Kgp, Rgp or HagA, the modulator includes an antagonist or is a binding protein useful as a diagnostic agent. For other proteins, the modulators in the form of antagonists, agonists and diagnostic agents may be useful. By using the atomic coordinates of K2 or K3 and the model for K1, to identify potential modulators from a larger group, it is possible to reduce the total number of molecules which need to be tested.
The modulators may be identified by a range of means including docking a three dimensional representation of a potential modulator with the three dimensional structure of K2 and/or K3. The computer representation of K2 and K3 is defined by atomic structural coordinates. In an embodiment, one or more modulators are docked into the Cleaved_Adhesin domain structure of K2 and/or K3. The method includes: (a) providing a three dimensional representation of the atomic coordinates of a Cleaved_Adhesin domain comprising or homologous to one or more of. K2 and K3 of Kgp and docking a three dimensional representation of a compound from a computer database with the three dimensional representation of K2 and/or K3; (b) determining a conformation of the resulting complex having a favorable geometric fit and favorable complementary interactions; and (c) identifying compounds that best fit K2 and/or K3 as potential modulators of K2 and/or K3 function and/or as potential diagnostic agents of K2 and/or K3 and/or potential antagonists, agonists or diagnostic agents for protein comprising a homologous Cleaved_Adhesin domain being K1, K2, K3, R1, R2 and one or more of A1 through A10.
The present disclosure further provides an isolated protein or fragment thereof comprising a Cleaved_Adhesin domain identified by the method of subjecting amino acid sequences of proteins to Cleaved_Adhesin domain modeling based on the amino acid sequences of one or more of K1, K2, K3, R1, R2 and/or A1 through A10 and selecting amino acid sequences having homology thereto wherein such identified amino acid sequences are regarded as defining a Cleaved_Adhesin domain.
Hence, provided herein are:
(i) a target on HA-comprising molecules from Porphyromonas gingivalis wherein the target comprises a Cleaved_Adhesin domain for antagonists and diagnostic agents;
(ii) recombinant polypeptide vaccines comprising Cleaved_Adhesin domains from the Porphyromonas gingivalis HA-comprising molecules as well as homologous domains from other proteins;
(iii) antagonists, agonists and diagnostic agents designed using the atomic coordinates surrounding or defining the Cleaved_Adhesin domains of HA-comprising molecules of Porphyromonas gingivalis, K1, K2, K3, R1, R2 and/or A1 through 10.
The atomic coordinates of K2 and K3 have been deposited in the protein Data Bank under 3KM5 and 3M1H, respectively which is incorporated herein by reference. They are also shown in
Nucleotide and amino acid sequences are referred to by a sequence identifier number (SEQ IN NO:). The SEQ ID NOs: correspond numerically to the sequence identifiers <400>1 (SEQ ID NO:1), <400>2 (SEQ ID NO:2), etc.
Table 1 provides a summary of the sequences identified for the Cleaved_Adhesin domains in Kpg K1 from strains W83, 381 and HG66, the Rpg R1 domain from strain HG66 and the Hag A domains A1-A10 from strains 281 and W83 of P. gingivalis. W83v refers to a variant strain of P. gingivalis.
Single and three letter abbreviations are used to define amino acid residues. these are summarized in Table 2.
Some figures contain color representations or entities. Color photographs are available from the Patentee upon request or from an appropriate Patent Office. A fee may be imposed if obtained from a Patent Office.
Throughout this specification, unless the context requires otherwise, the word “comprise”, or variations such as “comprises” or “comprising”, will be understood to imply the inclusion of a stated element or integer or step or group of elements or integers or steps but not the exclusion of any other element or integer or step or group of elements or integers or steps.
As used in the subject specification, the singular forms “a”, “an” and “the” include plural aspects unless the context clearly dictates otherwise. Thus, for example, reference to “a domain” includes a single domain, as well as two or more domains; reference to “an antagonist” includes a single antagonist, as well as two or more antagonists; reference to “the disclosure” includes a single aspect or multiple aspects of the disclosure; and so forth.
Adhesin and/or carbohydrate binding regions of proteins expressed by Porphyromonas gingivalis are subject to Cleaved_Adhesin Domain Family modeling (Finn et al., 2008 supra). Particular domains identified are referred to as K1, K2 and K3 on lysine gingipain (Kgp) and their equivalents on arginine gingipain (Rgp) [R1 and R2] and hemagglutinin A (HagA) [A1 through A10, inclusive].
Crystal structure determination of the K2 and K3 domains on Kgp confirms the topology of these domains and indicates that K2 functions as a hemolysin. The atomic coordinates for K2 and K3 are provided in Protein Data Bank under identifiers 3KM5 and 3M1H, respectively the contents of which are incorporated by reference. The present disclosure contemplates, therefore, a domain structure for the hemagglutinin (HA) region of protease-like molecules expressed by microorganisms which acquire iron, heme or porphyrin from biological environments generally, but not exclusively, for growth. The identified Cleaved_Adhesin domains also have homologs in a range of proteins from organisms not necessarily related to P. gingivalis. The identification of these domains also provides scope to generate therapeutic and diagnostic agents for a range of microorganisms and/or which target particular proteins.
The domains identified herein by Cleaved_Adhesin domain modeling (Finn et al., 2008 supra) are referred to as “Cleaved_Adhesin domains”. The Cleaved_Adhesin domains are identified within the hemagglutinin (HA) region of a protease-like molecule expressed on the surface or secreted by a Porphyromonas gingivalis or related microorganism. Homologous domains are identified in a range of proteins as summarized in http://pfam.sanger.ac.uk//family?acc=PF07675#tbaview=tab6.
The protease-like molecules contemplated herein include particular gingipains (gp's) such as lysine gingipain (Kgp) and arginine gingipain (Rgp) and hemagglutininA (HagA). The particular Cleaved_Adhesin domains on Kgp are referred to as K1, K2 and K3. Each of K1, K2 and K3 is defined by the amino acid sequences set forth in SEQ ID NOs:1 to 3, 10, 13, 14, 19, 22, 23, 25 and 31 (see Table 1), for particular strains of P. gingivalis. Reference to “K1”, “K2” and “K3” on Kgp from P. gingivalis includes functional equivalents or homologs on other protease-like molecules from P. gingivalis or from related microorganisms. Such functional equivalents or homologs include domains R1 and R2 on Rgp (defined by SEQ ID NOs:4 and 20). Similar Cleaved_Adhesin domains are also referred to as A1, A2, A3, A4, A5, A6, A7, A8, A9 and A10 in HagA (SEQ ID NOs:5 to 9, 11, 12, 15 to 18, 21, 24 and 26 to 30). A “protease-like molecule” includes a molecule having an HA region and which has amino acid sequence homology or catalytic activity of a cysteine protease. The term extends to HagA and other Hag proteins. The present disclosure extends to Cleaved_Adhesin domain containing proteins having Cleaved_Adhesin domains homologous to those exemplified herein expressed by other strains of Porphrymonas or unrelated microorganisms or present in related or unrelated proteins as summarized at http://pfam.sanger.ac.uk//family?acc=PF07675#tbaview=tab6.
It is proposed to use the K1, K2 and/or K3 domains or their equivalents or homologs such as R1 and R2 and A1 through A10 to identify antagonists of the activity of proteins carrying all or some of these domains. By “antagonizing the activity” includes inhibiting or reducing hemolysin or hemolytic activity of erythrocytes. These domains also provide targets for diagnostic agents to monitor infection and treatment protocols. These domains can also be used to identify other similar Cleaved_Adhesin domains in a range of related and un-related proteins. Such domains are useful targets for antagonists, agonists and diagnostic agents.
Reference to an “equivalent” or “homolog” of K1, K2 and K3 or R1 and R2 or A1 through A10 includes structural or sequence identity as well as domains having conformational, functional or sequence similarity or homology to K1, K2, K3, R1, R2 or A1 through A10. Generally, an “equivalent” or “homolog” includes a domain also deemed to be a Cleaved_Adhesin domain.
Accordingly, Cleaved_Adhesin domains are defined herein within the adhesin/carbohydrate region of a microbial molecule involved in hemolysis or hemolytic activity of erythrocytes and their use in the manufacture of medicaments for the treatment or prophylaxis of infection in the biological environment by the microorganism.
Hence, a method is contemplated for the prophylaxis or treatment of infection by a microorganism in a biological environment from where the microorganism acquires iron, heme or porphyrin, the method comprising administering to the environment an effective amount of an agent for a time and under conditions sufficient to antagonize a Cleaved_Adhesin domain with the adhesin and/or carbohydrate binding region of a protease-like molecule produced by the microorganism, the domain associated with hemolysis or hemolytic activity of erythrocytes.
The term “biological environment” is used in its broadest context to include an environment comprising porphyrin-containing molecules. Particular porphyrin-containing molecules include hemoglobin and its precursors as well as heme such as found in erythrocytes. In an embodiment, the biological environment is a vascular region or cavity or a mucosal membrane in an animal species such as a mammal, reptile, amphibian, fish or bird or is a hoof of a livestock animal comprising erythrocytes or other heme-containing cells. In an embodiment, the animal is a mammal such as a human or livestock animal.
Accordingly, the present disclosure provides a method for the prophylaxis or treatment of infection by a microorganism in a mammal from where the microorganism acquires iron, heme or porphyrin, the method comprising administering to the environment an effective amount of an agent for a time and under conditions sufficient to antagonize a Cleaved_Adhesin domain within an HA region of a molecule produced by the microorganism wherein the molecule is a protease-like molecule associated with hemolysis or hemolytic activity of erythrocytes.
In an embodiment, the disclosure relates to P. gingivalis infection in the oral cavity such as during periodontal disease. The instant disclosure extends to any disease condition resulting from microbial infection and in particular infection by P. gingivalis or a related microorganism involving the acquisition of iron, heme or porphyrin. Such microorganisms are required to acquire iron, heme or porphyrin as they do not possess a biosynthetic pathway for porphyrins. Examples of microorganisms related to P. gingivalis contemplated herein include but are not limited to Salmonella sp., Serratia sp, Yersinia sp, Klebsiella sp, Vibrio sp, Pseudomas sp, E. coli, Haemophilus sp and Bordetella sp. Examples of P. gingivalis or related microorganism infection contemplated by the present disclosure include infection of the oral cavity, nasopharynx, oropharynx, vagina and urethra as well as infection of mucosal membranes and infection of hooves of livestock animals such as sheep, cattle and goats. An “effective amount” means an amount sufficient to prevent or reduce hemolysis or hemolytic activity of erythrocytes. The effective amount may also be determined by an amount sufficient to inhibit growth of a microorganism such as P. gingivalis.
In another aspect, a method is provided for the prophylaxis or treatment of infection by Porphyromonas gingivalis or a related organism in a mammal, the method comprising administering to the mammal an effective amount of an agent for a time and under conditions sufficient to antagonize a Cleaved_Adhesin domain within the HA region of a gingipain or HagA, wherein the antagonism prevents or reduces hemolysis or hemolytic activity of erythrocytes.
The present disclosure also contemplates a method for prophylaxis or treatment of periodontal, pulmonary, vaginal, urethral or hoof disease resulting from infection by P. gingivalis or related microorganism in a mammal, the method comprising administering to the mammal an effective amount of an agent for a time and under conditions sufficient to antagonize, a Cleaved_Adhesin domain within the HA region of a gingipain or HagA, wherein the antagonism prevents or reduces hemolysis or hemolytic activity of erythrocytes.
Reference herein to “Porphyromonas gingivalis” or its abbreviation “P. gingivalis” includes reference to all strains, mutants, derivatives and variants of this organism as well as serological sub-types. The present disclosure further extends to microorganisms related to P. gingivalis at the metabolic, structural, biochemical, immunological and/or disease causing levels. Examples of related microorganisms are those listed above.
The present disclosure provides in an embodiment, a method for the prophylaxis or treatment of infection by a microorganism in a biological environment from where the microorganism acquires iron, heme or porphyrin, the method comprising administering to the environment an effective amount of an agent for a time and under conditions sufficient to antagonize a Cleaved_Adhesion domain within an adhesin and/or carbohydrate binding region of a molecule produced by the microorganism, the domain associated with hemolysis or hemolytic activity of erythrocytes, wherein the domain is defined by Cleaved_Adhesin Domain modeling.
As indicated above, provided are Cleaved_Adhesin domains K1, K2 and K3 on Kgp and their equivalents on Rgp (R1 and R2) and HagA [A 1 through A10] (See
In another aspect, a method is provided for identifying a protein or part thereof which comprises a Cleaved_Adhesin domain, the method comprising subjecting amino acid sequences of proteins to Cleaved_Adhesin domain modeling based on the amino acid sequences of one or more of K1, K2, K3, R1, R2 and/or A1 through A10 and selecting amino acid sequences having homology thereto wherein such identified amino acid sequences are regarded as defining a Cleaved_Adhesin domain. By “homology” is meant an amino acid sequence identified by multiple sequence alignment of known Cleaved_Adhesin domains such as K1, K2, K3, R1, R2 and two or more of A1 through A10. In an embodiment, multiple sequence alignment modeling is used to identify homologous Cleaved_Adhesin domains in other proteins. In particular, the K1 sequence is aligned with the sequence of the K3 domain (
The present disclosure further provides an isolated protein or fragment thereof comprising a Cleaved_Adhesin domain identified by the method of subjecting amino acid sequences of proteins to Cleaved_Adhesin domain modeling based on the amino acid sequences of one or more of K1, K2, K3, R1, R2 and/or A1 through A10 and selecting amino acid sequences having homology thereto wherein such identified amino acid sequences are regarded as defining a Cleaved_Adhesin domain.
Another aspect herein is directed to a method for the treatment or prophylaxis of infection by Porphyromonas gingivalis or a related microorganism in a mammal, the method comprising administering to the mammal an antagonizing effective amount of an agent which antagonizes function of one or more of Cleaved_Adhesin domains K1, K2 and/or K3 on Kgp and/or R1 and/or R2 on Rgp and/or A 1 through A10.
The term “infection” is used in its most general sense and includes the presence or growth of P. gingivalis or related microorganism resulting in a disease condition or having the capacity to result in a disease condition. The term “infection” further encompasses P. gingivalis or related microorganism when present as part of the normal flora. Such bacteria may, under certain circumstances, be responsible for disease development. Prophylaxis is contemplated herein to reduce the levels of P. gingivalis or related microorganism or to reduce the likelihood of a disease condition developing resulting from infection by P. gingivalis or astructurally related organism.
The present disclosure teaches the treatment of P. gingivalis or a related microorganism in humans. The disclosure extends to the prophylaxis or treatment of P. gingivalis or related microorganisms in other mammals such as primates, livestock animals (e.g. sheep, cows, goats, pigs, horses, donkeys), companion animals (e.g. dogs, cats), laboratory test animals (e.g. mice, rats, guinea pigs, rabbits, hamsters) and captured wild animals. The disclosure also teaches the prophylaxis or treatment of animals such as reptiles, amphibians, fish and avian species. All recipients of treatment of prophylaxis are included by the terms “subject”.
Infection by P. gingivalis or related microorganism in accordance with this aspect of the present disclosure is one leading to or having the potential to lead to an infection of a mucosal or vascular region such in the oral cavity, nasopharynx, oropharynx, vagina or urethra as well as the hooves of farm animals.
The term “antagonize” means and includes reducing, inhibiting or otherwise adversely affecting a Cleaved_Adhesin domain on the microbial surface molecule to the extent to reduce or inhibit hemolysis or hemolytic-like activity. The functional result of such antagonism is the inability or at least reduced capacity of P. gingivalis or related microorganism from acquiring iron, heme or porphyrin for use in, for example, metabolic pathways. Antagonism may be complete, i.e. from about 90-100% or partial, i.e. from about 30 to about 90% as determined by hemolytic assays or inhibition of P. gingivalis growth or maintenance.
The sequence identifiers defining K1, K2, K3, R1, R2 and A1 through A10 are summarized in Table 1. The sequences were determined from different strains of P. gingivalis.
Accordingly, the present disclosure teaches a method for the treatment or prophylaxis of infection of a subject by Porphyromonas gingivalis or related microorganism, the method comprising administering to the mammal an effective amount of an agent which antagonizes the function of an amino acid sequence selected from K1, K2 and/or K3 on Kgp or an amino acid sequence selected from R1 and/or R2 on Rgp or an amino acid sequence selected from A1 through A10 or HagA or a homolog thereof having at least 10% amino acid sequence similarity thereto after optimal alignment, the function antagonized including hemolytic function of erythrocytes. The subject may be a mammal such as a human or a non-mammalian animal.
This aspect extends to the use of a Cleaved_Adhesin domain-interacting molecule directed to K1, K2, K3, R1, R2 and/or one or more of A1 through A10 or another protein or a homolog or similog thereof in the manufacture of a medicament or diagnostic agent.
This aspect also extends to antibodies to Cleaved_Adhesin domain or an epitope therein. Antibodies may be monoclonal or polyclonal or synthetic or derivatized forms thereof.
The terms “similarity” and “homology” as well as “homologs” and “similogs” as used herein include exact identity between compared sequences at the or amino acid level. Where there is non-identity at the amino acid level, “similarity” includes amino acids that are nevertheless related to each other at the structural, functional, biochemical and/or conformational levels.
Terms used to describe sequence relationships between two or more polypeptides include “reference sequence”, “comparison window”, “sequence similarity”, “sequence identity”, “percentage of sequence similarity”, “percentage of sequence identity”, “substantially similar” and “substantial identity”. A “reference sequence” is at least 12 but frequently 15 to 18 and often at least 25 or above, such as 30 amino acid units. A “comparison window” refers to a conceptual segment of typically 12 contiguous residues that is compared to a reference sequence. The comparison window may comprise additions or deletions (i.e. gaps) of about 20% or less as compared to the reference sequence (which does not comprise additions or deletions) for optimal alignment of the two sequences. Optimal alignment of sequences for aligning a comparison window may be conducted by computerized implementations of algorithms (GAP, BESTFIT, FASTA, and TFASTA in the Wisconsin Genetics Software Package Release 7.0, Genetics Computer Group, 575 Science Drive Madison, Wis., USA) or by inspection and the best alignment (i.e. resulting in the highest percentage homology over the comparison window) generated by any of the various methods selected. Reference also may be made to the BLAST family of programs as for example disclosed by Altschul et al., Nucl. Acids Res. 25:3389, 1997. A detailed discussion of sequence analysis can be found in Unit 19.3 of Ausubel et al., Current Protocols in Molecular Biology, John Wiley and Sons Inc, 1994-1998, Chapter 15.
The terms “sequence, similarity” and “sequence identity” as used herein refers to the extent that sequences are identical or functionally or structurally similar on a an amino acid-by-amino acid basis over a window of comparison. Thus, a “percentage of sequence identity”, for example, is calculated by comparing two optimally aligned sequences over the window of comparison, determining the number of positions at which the identical amino acid residue (e.g. Ala, Pro, Ser, Thr, Gly, Val, Leu, Ile, Phe, Tyr, Trp, Lys, Arg, His, Asp, Glu, Asn, Gln, Cys and Met) occurs in both sequences to yield the number of matched positions, dividing the number of matched positions by the total number of positions in the window of comparison (i.e., the window size), and multiplying the result by 100 to yield the percentage of sequence identity. For the purposes of the present disclosure, “sequence identity” will be understood to mean the “match percentage” calculated by the DNASIS computer program (Version 2.5 for windows; available from Hitachi Software engineering Co., Ltd., South San Francisco, Calif., USA) using standard defaults as used in the reference manual accompanying the software. Similar comments apply in relation to sequence similarity.
Reference to “at least 10% similarity” includes from about 10 to 100% similarity such as at least 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33; 34, 35, 36, 37, 38, 19, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, 52, 53, 54, 55, 56, 57, 58, 59, 60, 61, 62, 63, 64, 65, 66, 67, 68, 69, 70, 71, 72, 73, 74, 75, 76, 77, 78, 79, 80, 81, 82, 83, 84, 85, 86, 87, 88, 89, 90, 91, 92, 93, 94, 95, 96, 97, 98, 99 or 100% similarity. The term “homology” may also be used.
The identification of the Cleaved_Adhesin domains within the hemagglutinin region of Porphyromonas gingivalis gingipains and hemagglutininA provides a means for screening for antagonists of the function of these domains. Such antagonists are useful, for example, in the development of vaccines and therapeutic compositions for preventing or treating infection by P. gingivalis or related microorganisms. The domains also provide diagnostic targets. The present disclosure teaches the use of the K1, K2 and K3 and/or R1 and R2 and/or A1 through A 10 or their equivalent domains to produce a vaccine based on a recombinant protein, a vaccine based on a 3D epitope within the domain or an agent such as a carbohydrate which inhibits hemolytic- and/or adhesin-mediated activity.
Hence, the present disclosure teaches:
(i) a target on HA-comprising molecules from Porphyromonas gingivalis wherein the target comprises a Cleaved_Adhesin domain for antagonists and diagnostic agents;
(ii) recombinant polypeptide vaccines comprising Cleaved_Adhesin domains from the Porphyromonas gingivalis HA-comprising molecules as well as homologous domains from other proteins;
(iii) antagonists and diagnostic agents designed using the atomic coordinates surrounding or defining the Cleaved_Adhesin domains of HA-comprising molecules of Porphyromonas gingivalis, K1, K2, K3, R1, R2 and/or A1 through 10.
Another aspect taught herein is an agent capable of functionally antagonizing a Cleaved_Adhesin domain on a gingipain or hemagglutinin-binding protein or Porphyromonas gingivalis or related organism.
In an embodiment, the agent antagonizes hemolytic and/or adhesin activity of Kgp, Rgp and/or HagA by targeting domain selected from K1, K2, K3, R1 and R2 and A1 through A10 or their equivalents.
Yet another aspect taught herein is an agent capable of functionally antagonizing a Cleaved_Adhesin domain which is homologous to a Cleaved_Adhesin domain selected from K1, K2, K3, R1, R2 and one or more of A1 through A10. These agents may also be useful as antagonists or diagnostic agents for Porphyromonas gingivalis infection or antagonists, agonists or diagnostic agents for the treatment or diagnosis of conditions including infection associated with proteins comprising the homologous Cleaved_Adhesin domains.
The agent may be a derivative of the gingipain or Hag protein or the agent may be a vaccine or formulation which targets the domain or is an agent identified from screening of a chemical library or following natural product screening. The latter includes screening of environments such as aquatic environments, coral, seabeds, microorganisms, plants and Antarctic environments for naturally occurring molecules capable of acting as antagonists. The agents also include antibodies such as monoclonal or polyclonal antibodies, synthetic antibody derivatives, humanized or mammalianized antibodies and the like. Alternatively, the agent may be identified by modeling of the crystal structure of the domain. In one particular embodiment, the K2 or K3 crystal structure is determined and, hence, this may be used to identify potentially interacting molecules.
The identified domains alone or as part of a carrier molecule may be used as vaccine components to generate antibodies to the domain or their immunological relatives. Alternatively, the antagonist may be an antibody to the domain or an antibody to another region resulting in reduced function of the domain. Yet in another alternative, the antagonists form part of a therapeutic or prophylactic composition or formulation. The term “vaccine” is used to cover formulations which are designed to induce an immune response as well as formulations comprising antagonists of the Cleaved_Adhesin domains.
The antagonists, therefore, may be peptides, polypeptides, proteins, antibodies, small or large chemical entities or combinations thereof and may be in an isolated, naturally occurring form or may be in recombinant or chemically synthetic form.
Screening for antagonists may be accomplished in any number of ways. In one method, preparations of gingipains or hemagglutinin-binding molecules or parts thereof are incubated with potential antagonists and then subjected to chromatography or gel electrophoresis or immunoassay to screen for the formation of a complex. In another embodiment, 3D modeling or epitope screening is employed. In yet another embodiment, recombinant vaccines are prepared comprising peptides, polypeptides or proteins which comprise a Cleaved_Adhesin domain from a gingipain or Hag protein from P. gingivalis or a homologous domain from another protein whether related to gingipain/Hag protein or not.
In addition to screening for suitable antagonists, the present disclosure enables the chemical synthesis and/or rational design for developing Cleaved_Adhesin domain. In particular, data presented herein show that the K2 domain is a “jelly-roll” fold with two anti-parallel β-sheets. Hence, one approach is to target the fold or an epitope formed within the domain.
Accordingly, another aspect of the disclosure provides an agent capable of binding or interacting with a domain selected from K1, K2, K3, R1 and R2 and A1 through A10 or an equivalent thereof or an epitope or sub-region therein, the agent antagonizing the function of the domain. Similar agents are also contemplated for use as diagnostic agents.
When the Cleaved_Adhesin domain-containing molecules or derivatives, analogs or homologs thereof are used in a vaccine composition, they are generally used as an immunogenic component to stimulate an immune response against the domain. They may also generate an immune response to other domains since this may cause conformational changes preventing protein function.
Accordingly, another aspect enabled by the present disclosure is a composition such as therapeutic or vaccine composition comprising an agent as hereinbefore described and one or more pharmaceutically acceptable carriers and/or diluents.
The immunogenic component of a vaccine composition as contemplated herein exhibits therapeutic activity, for example, in the prophylaxis and/or treatment of P. gingivalis infection when administered in an amount which depends on the particular case. For example, for recombinant peptide, polypeptide or protein molecules, from about 0.5 μg to about 20 mg, may be administered, particularly from about 1 μg to about 10 mg, particularly from about 10 μg to about 5 mg, particularly from about 50 μg to about 1 mg equivalent of the immunogenic component in a volume of about 0.01 ml to about 5 ml or from about 0.1 ml to about 5 ml. A feature is to administer sufficient immunogen to induce a protective immune response. The above amounts can be administered as stated or calculated per kilogram of body weight. Dosage regime can be adjusted to provide the optimum therapeutic response. For example, several divided doses can be administered or the dose can be proportionally reduced as indicated by the exigencies of the therapeutic situation. Booster administration may also be required.
The vaccine or other therapeutic composition taught by the present disclosure can further comprise one or more additional immunomodulatory components such as, for example, an adjuvant or cytokine molecule, amongst others, which is capable of increasing the immune response against the immunogenic component. Non-limiting examples of adjuvants that can be used in the vaccine of the present disclosure include the RIBI adjuvant system (Ribi Inc., Hamilton, Mont., USA), alum, mineral gels such as aluminium hydroxide gel, oil-in-water emulsions, water-in-oil emulsions such as, for example, Block co-polymer (CytRx, Atlanta Ga., USA), QS-21 (Cambridge Biotech Inc., Cambridge Mass., USA), SAF-M (Chiron, Emeryville Calif., USA), AMPHIGEN adjuvant, Freund's complete adjuvant; Freund's incomplete adjuvant; and Saponin, QuilA or other saponin fraction, monophosphoryl lipid A, and Avridine lipid-amine adjuvant. Other immunomodulatory agents that can be included in the vaccine include, for example, one or more cytokines, such as interferon and/or interleukin, or other known cytokines. Non-ionic surfactants such as, for example, polyoxyethylene oleyl ether and n-hexadecyl polyethylene ether may also be included in the vaccines taught herein.
The vaccine or other composition can be administered in any convenient manner such as by oral, intravenous (where water soluble), intramuscular, subcutaneous, intranasal, intradermal or suppository routes or by implantation (e.g. using slow release technology). Depending on the route of administration, the immunogenic component may be required to be coated in a material to protect it from the action of enzymes, acids and other natural conditions which may inactivate it, such as those in the digestive tract.
The vaccine or other composition may also be administered parenterally or intraperitoneally. Dispersions can also be prepared in glycerol, liquid polyethylene glycols, and mixtures thereof, or in oils. Under ordinary conditions of storage and use, these preparations can contain a preservative to prevent the growth of microorganisms. Alternatively, the vaccine composition can be stored in lyophilized form to be rehydrated with an appropriate vehicle or carrier prior to use.
The vaccine or other composition may also be within form of a mouthwash, toothpaste and the like.
Pharmaceutical forms suitable for injectable use include sterile aqueous solutions (where water soluble) or dispersions and sterile powders for the extemporaneous preparation of sterile injectable solutions or dispersions. In all cases the form must be fluid to the extent that easy syringeability exists, unless the pharmaceutical form is a solid or semi-solid such as when slow release technology is employed or it may be deliverable by spray, inhalation, nasal drip or microdroplets. In any event, it must be stable under the conditions of manufacture and storage and must be preserved against the contaminating action of microorganisms.
The carrier may be a solvent or dispersion medium containing, for example, water, ethanol, polyol (for example, glycerol, propylene glycol and liquid polyethylene glycol, and the like), suitable mixtures thereof and vegetable oils. The proper fluidity can be maintained, for example, by the use of a coating such as lecithin, by the maintenance of the required particle size in the case of dispersion and by the use of surfactants. The prevention of the action of microorganisms can be brought about by various antibacterial and antifungal agents such as, for example, parabens, chlorobutanol, phenol, sorbic acid, thimerosal and the like. In many cases, it will be preferable to include isotonic agents such as, for example, sugars or sodium chloride. Prolonged absorption of the injectable compositions can be brought about by the use in the compositions of agents delaying absorption such as, for example, aluminum monostearate and gelatin.
Sterile injectable solutions are prepared by incorporating the active compound in the required amount in the appropriate solvent with various of the other ingredients enumerated above, as required, followed by filter-sterilization. Generally, dispersions are prepared by incorporating the sterilized active ingredient into a sterile vehicle which contains the basic dispersion medium and the required other ingredients selected from those enumerated above. In the case of sterile powders for the preparation of sterile injectable solutions, the preferred methods of preparation are vacuum drying and the freeze-drying technique which yield a powder of the active ingredient plus any additional desired ingredient from previously sterile-filtered solution thereof.
The present disclosure further provides vaccine compositions which confer protection against infection by one or more isolates or sub-types of P. gingivalis including those that belong to the same serovar or serogroup as P. gingivalis. The vaccine composition may also confer protection against infection by other species of the genus Prophyromonas or other microorganisms related thereto as determined at the nucleotide, biochemical, structural, physiological and/or immunointeractive level; the only requirement being that said other species or other microorganism produce a peptide, polypeptide or protein which is immunologically cross-reactive to the Cleaved_Adhesin domain containing molecule of P. gingivalis. For example, such related microorganisms may comprise genomic DNA which is at least about 70% similar overall to the genomic DNA of P. gingivalis as determined using standard genomic DNA hybridization and analysis techniques. By “at least 70%” means from about 70 to 100% such as 70, 71, 72, 73, 74, 75, 76, 77, 78, 79, 80, 81, 82, 83, 84, 85, 86, 87, 88, 89, 90, 91, 92, 93, 94, 95, 96, 97, 98, 99 or 100%.
The present disclosure teaches serogroup and serovar variants of P. gingivalis and its related microorganisms. The terms “serogroup” and “serovar” relate to a classification of microorganisms which is based upon serological typing data, in particular data obtained using agglutination assays such as the microscopic agglutination test (MAT). Those skilled in the art will be aware that serovar and serogroup antigens are a mosaic on the cell surface and, as a consequence there will be no strict delineation between bacteria belonging to a serovar and/or serogroup. Moreover, organisms which belong to different species may be classified into the same serovar or serogroup because they are indistinguishable by antigenic determination. As used herein, the term “serovar” means one or more P. gingivalis strains which is/are antigenically-identical with respect to antigenic determinants produced by one or more loci. Quantitatively, serovars may be differentiated from one another by cross-agglutination absorption techniques. As used herein, the term “serogroup” refers to a group of Porphyromonas spp. whose members cross-agglutinate with shared group antigens and do not cross-agglutinate with the members of other groups and, as a consequence, the members of a serogroup have more or less close antigenic relations with one another by simple cross-agglutination.
The present disclosure teaches therapeutic and/or prophylactic compositions capable of conferring protection against a “genetic variant” of P. gingivalis, the only requirement being that such a variant produce a peptide, polypeptide or protein having a Cleaved_Adhesin domain equivalent or similar to K1, K2 and/or K3 of Kgp and/or R1 and/or R2 of Rgp.
The present disclosure also teaches combination formulations comprising an effective amount of an immunogenic component comprising or within the Cleaved_Adhesin domain combined with an effective amount of one or more other antigens or other therapeutic molecules capable of protecting the subject against other pathogens or disease conditions.
Also taught is the use of a Cleaved_Adhesin domain on a gingipain or a hemagglutinin-binding molecule in the manufacture of a medicament for the prevention or treatment of infection by P. gingivalis or related microorganism.
In a related aspect, there is provided a use of an antagonist of interaction between a HA2-containing molecule from P. gingivalis or related microorganism and a porphyrin-containing molecule such as but not limited to hemoglobin or a precursor form thereof or part thereof such as heme in the manufacture of a medicament for the prophylaxis or treatment of P. gingivalis infection.
The use of the Cleaved_Adhesin domains such as K1, K2, K3, R1, R2 and one or more of A1 through A10 and their homologs and equivalents is also provided for diagnostic targets to detect infection by P. gingivalis and its related organisms including monitoring the efficacy of a therapeutic protocol and/or to identify potential relapses in infection. The diagnostic assay can also be used to determine minimal disease resistance (MDR). The diagnostic assay may take any form such as but not limited to an antibody based assay such as a ELISA, Western blots, dip-stick assays, protein microarrays and the like. The present disclosure teaches antibodies and other reagents specific for the Cleaved_Adhesin domains as herein described and their use in the manufacture of diagnostic kits to detect and/or monitor infection.
further provided is the use of the amino acid sequence set forth in K1, K2, K3, R1, R2 and one or more of A1 through A10 in the identification of a Cleaved_Adhesin domain in a protein or to identify a protein comprising a Cleaved_Adhesin domain.
The present disclosure further contemplates the use of the atomic coorindates for K2 or K3 or the model for K1 to design or identify a range of mimetic antagonists, agonists or other interacting compounds.
The term “atomic structural coordinates” as used herein refers to a data set that defines the three dimensional structure of a Cleaved_Adhesin domain and in particular define K2 and K3 of Kgp and further define a model for K3. Structural coordinates can be slightly modified and still render nearly identical three dimensional structures. A measure of a unique set of structural coordinates is the root-mean-square deviation of the resulting structure. Structural coordinates that render three dimensional structures that deviate from one another by a root-mean-square deviation of less than about 1.5 Å may be viewed by a person of ordinary skill in the art as identical.
X-ray crystallography is used to elucidate the three dimensional structure of crystalline forms of K2 and K3 of the present disclosure. Typically, the first characterization of crystalline forms by X-ray crystallography can determine the unit cell shape and its orientation in the crystal. The term “unit cell” refers to the smallest and simplest volume element of a crystal that is completely representative of the unit of pattern of the crystal. The dimensions of the unit cell are defined by six numbers: dimensions a, b and c and angles α, β and γ. A crystal can be viewed as an efficiently packed array of multiple unit cells. Detailed description of crystallographic terms are described in Hahn, The International Tables for Crystallography, volume A, Fourth Edition, Kluwer Academic Publishers 1996 and Shmueli, The International Tables for Crystallography, Volume B, First Edition, Kluwer Academic Publishers.
The present disclosure enables the identification of potential modulators of proteins having a Cleaved_Adhesin domain homologous to or comprising a domain selected from K1, K2, K3, R1, R2 and one or more of A1 through A10. In relation to a modulator of Kgp, Rgp or HagA, the modulator includes an antagonist or is a binding protein useful as a diagnostic agent. For other proteins, the modulators in the form of antagonists, agonists and diagnostic agents may be useful. By using the atomic coordinates of K2 or K3 and the model for K1, to identify potential modulators from a larger group, it is possible to reduce the total number of molecules which need to be tested.
The modulators may be identified by a range of means including docking a three dimensional representation of a potential modulator with the three dimensional structure of K1, K2 and/or K3. The computer representation of K2 and K3 is defined by atomic structural coordinates, similarly, the K1 model. In an embodiment, one or more modulators are docked into the Cleaved_Adhesin domain structure of K1, K2 and/or K3. The method includes: (a) providing a three dimensional representation of the atomic coordinates of a Cleaved_Adhesin domain comprising or homologous to one or more of K1, K2 and K3 of Kgp and docking a three dimensional representation of a compound from a computer database with the three dimensional representation of K1, K2 and/or K3; (b) determining a conformation of the resulting complex having a favorable geometric fit and favorable complementary interactions; and (c) identifying compounds that best fit K1, K2 and/or K3 as potential modulators of K1, K2 and/or K3 function and/or as potential diagnostic agents of K1, K2 and/or K3 and/or potential antagonists, agonists or diagnostic agents for protein comprising a homologous Cleaved_Adhesin domain.
Conveniently, the atomic coordinates for K2 and K3 are shown in
The term “docking” refers to the process of placing a three dimensional representation of the compound in close proximity with the three dimensional representation of K1, K2 and/or K3. In an embodiment, the docking process refers to finding low energy conformations of the resulting compound/K1, K2 and/or K3 complex.
The term “favorable geometric fit” refers to a conformation of the compound/K1, K2 and/or K3 complex where the surface area of the compound is in close proximity with the surface of K1, K2 and/or K3 without unfavourable interactions (i.e. steric hindrances, etc).
Yet another aspect taught herein includes is a method of identifying potential modulation of the function of a protein which comprises a Cleaved_Adhesin domain comprising of homolgous to K1, K2, K3, R1, R2 and one or more of A1 to A10 by operating modulator construction or modulator searching computer programs on the compounds complexed with K1, K2 and/or K3. The method comprises the steps of: (a) providing a three-dimensional representation of one or more compounds, complexed with K1, K2 and/or K3, where the computer representation of the compounds and K 1, K2 and/or K3 are defined by atomic structural coordinates; and (b) searching a database for compounds similar to the compounds, using a compound searching computer program or replacing portions of the compounds complexed with K1, K2 and/or K3 with similar chemical structures from a database using a compound construction computer program, where the representations of the compounds are defined by structural coordinates. The skilled artisan will recognize that a number of suitable computer programs are available for compound searching and construction, including UNITY (Trade Mark) [Tripos, Inc.] and CATALYST (Registered) [MSI, Inc.].
As used herein, “comprising” is synonymous with “including,” “containing,” or “characterized by,” and is inclusive or open-ended and does not exclude additional, unrecited elements or method steps. As used herein, “consisting of” excludes any element, step, or ingredient not specified in the claim element. As used herein, “consisting essentially of” does not exclude materials or steps that do not materially affect the basic and novel characteristics of the claim. Any recitation herein of the term “comprising”, particularly in a description of components of a composition or in a description of elements of a device, is understood to encompass those compositions and methods consisting essentially of and consisting of the recited components or elements. The present disclosure illustratively described herein suitably may be practiced in the absence of any element or elements, limitation or limitations which is not specifically disclosed herein.
When a group of substituents is disclosed herein, it is understood that all individual members of those groups and all subgroups, including any isomers and enantiomers of the group members, and classes of compounds that can be formed using the substituents are disclosed separately. When a compound is claimed, it should be understood that compounds known in the art including the compounds disclosed in the references disclosed herein are not intended to be included. When a Markush group or other grouping is used herein, all individual members of the group and all combinations and subcombinations possible of the group are intended to be individually included in the disclosure.
When a range is recited herein, it is intended that all subranges within the stated range, and all integer values within the stated range, are intended, as if each subrange and integer value was recited.
Aspects of the disclosure are further described by the following non-limiting Examples. In these Examples, materials and methods as outlined below are employed. Since the filing of the priority applications on which the present disclosure is based, aspects were published in Li et al., 2010 supra the entire contents of which are incorporated herein by reference.
Sequences of the HagA proteins and the HA regions of Kgp and RgpA were analyzed to identify possible homologous domains. A series of multiple sequence alignments were conducted using the program ClustalW (Laikin et al., Bioinformatics 23:2947-2948, 2007). Fragments of sequences with similarities were aligned and the putative domain boundaries of each of the fragments extended until a minimum of 30% pairwise sequence identity was present. The putative homologous regions of the proteins identified by this procedure are shown in
The gene fragment encoding the K2 domain (Ala1157-Gly1334) of Kgp from P. gingivalis W83 was cloned into vector pETM-21 at cloning sites of BamHI/XhoI. The construct was sequenced to confirm that there was no mutation present. The constructed plasmid was transformed into E. coli BL21(DE3) competent cells for protein expression. Cells were grown in LB medium with ampicillin (100 g/ml) at 37° C. until OD600 reached 0.6 and the temperature was reduced to 20° C. IPTG was added to a final concentration of 0.1 mM to induce protein expression. The recombinant K2 protein with six histidines at the N-terminus was purified using Ni-NTA (Novagen) affinity chromatography. After removal of the N-terminal 6×His-tag by thrombin cleavage at room temperature, non-tagged recombinant K2 was further purified by size exclusion chromatography using a Superdex 75 16/60 column (Amersham). Approximately 20 mg protein was obtained from a 1 L culture.
Selenomethionine-substituted protein was expressed using the Overnight Express (Trade Mark) Autoinduction System (Novagen) and purified using the same methods as for native protein. They were both concentrated to 15 mg/mL in buffer comprising 10 mM Tris pH 7.6 and 150 mM NaCl. Protein concentration was determined by UV absorbance at 280 nm with a molar extinction coefficient for K2 of 39545 M−1 cm−1. The dispersity of purified protein samples with concentrations were monitored by dynamic light scattering using a Protein Solutions Dynapro instrument at 20° C.
Circular dichroism spectra were recorded on a Jasco 720 circular dichroism spectropolarimeter over a wavelength range of 184-260 nm with 0.5 nm resolution using a quartz cell with 1.00 mm pathlength. The K2 and the Kgp treated K2 purified proteins were prepared for analysis in 10 mM Na borate at a concentration of 7.7 μM.
The gene fragment encoding the K3 domain (Ala1427-Gly1602) of Kgp from P. gingivalis W83 (gene code AF017059 and protein ID O52050) were cloned as previously described for K2 (Li et al., 2010 supra). The gene encoding the K1 domain (Gly982-Gly1154) and the constructs for K1K2 (Gly982-Gly1334) and K1K2K3 (Gly982-Leu1661) derived from cDNA were cloned into pGEX-6P-1 vector (Amersham) at the cloning sites of BamHI/XhoI. DNA sequencing of the cloned gene fragments revealed five differences with the published sequence (gene code AF017059) which have mutated 1351Asn to Lys, 1364Tyr to Asp, 1390Asp to Asn, 1448His to Asp and 1479His to Tyr. Each of these mutations was confirmed by sequencing to be present in the cDNA of kgp used as the PCR template. Each of the five specific mutations is found in another kgp entry for P. gingivalis W83 with a gene code of AE015924 and protein code of PG1844. Based on this information, it was concluded that these mutations probably occur spontaneously in nature. Nucleotides coding for two additional residues, Gly-Ser were added to the N-terminus in the K3 construct following the 6×His-tag and the thrombin cleavage site. Five additional residues Gly-Pro-Leu-Gly-Ser were added to the N-terminus in the K1, K1K2 and K1K2K3 constructs following the GST fusion partner and the PreScission protease cleavage site.
The constructed plasmids were transformed to E. coli BL21 (DE3) competent cells for protein expression. The expression and purification of recombinant K3 protein with 6×His-tag at the N-terminus followed the same procedure as previously described for the K2 domain (Li et al., 2010 supra). After removing the N-terminal 6×His-tag by thrombin cleavage, the K3 protein was further purified by size exclusion chromatography in a buffer containing 10 mM Tris pH7.6 and 150 mM NaCl.
Similarly, the recombinant proteins, K1, K1K2 and K1K2K3 each with a GST fusion partner at the N-terminus were purified using Glutathione Sepharose 4B affinity chromatography. The beads bound with protein were washed with PreScission protease cleavage buffer containing 50 mM Tris pH 7.0, 150 mM NaCl and 1 mM DTT, followed by protease cleavage. The eluted proteins were further purified by gel filtration chromatography using Superdex 75 Hiload 16/60 or Superdex 200 Hiload 16/60 columns (Amersham) according to the size of the proteins with a running buffer of 10 mM Tris pH 7.6, 150 mM NaCl and 0.5 mM CaCl2. The protein buffer solutions were exchanged to 10 mM Tris pH 7.6 and 150 mM NaCl, leaving additional non-bound Ca2+ at <0.5 mM post-dialysis to avoid the formation of calcium salt crystals during crystallization screening. The purified proteins were concentrated to 10-15 mg/ml determined by UV absorbance at 280 nm.
Crystallization screenings of the K2 domain were performed by hanging-drop vapour-diffusion method using Mosquito (TTP LabTech), a Nano-drop crystallization robot, and 96-well screening kits (Qiagen). Equal volumes (0.2 μl) of protein (15 mg/mL) and reservoir solution were mixed together and incubated. Initially clusters of needle-shaped crystals were observed under the condition of 0.2 M NH4NO3 and 2.2 M (NH4)2SO4. To improve the quality of crystals, micro-seeding was performed using cat's whiskers. The larger needle shaped crystals used for X-ray diffraction were grown in the refined conditions of 0.2M NH4NO3, 0.1 M Na citrate pH 5.6 and 2.0 M (NH4)2SO4 after 7 days of incubation at 23° C. Selenomethionine-substituted crystals were obtained under the same conditions. The crystals were cryo-protected by adding 5-20% glycerol to the mother liquor and then flash-cooled in a N2 stream at 100° K for data collection.
Selenomethionine MAD data were collected at three wavelengths near the selenium Kα absorption edge: λ1=0.97949 Å (peak); λ2=0.97962 Å (inflection); λ3=0.94947 Å (a high energy remote) on the beam line 23ID-B at the Advanced Photon Source, Argonne National Laboratory, using a Mar 300 CCD detector. A total of 180 successive frames in each set were collected with a 1° oscillation for each frame. A 1.4 Å native data set was collected later on the beam line 3BM1, Australian Synchrotron, Melbourne, using an ADSC Quantum 210r CCD detector. Intensities were integrated and processed using the HKL2000 program (Otwinowski and Minor, Macromolecular Crystallography, Pt A276:307-326, 1997). Both the native and Se-Met crystals belong to P21 space group with similar unit cell dimensions (a=30, b=60, c=86 Å and β=94°). Solvent-content analysis indicated that the asymmetric unit contained two molecules with a Matthews coefficient (VM) of 2.0 Å3/Da (38% solvent content). The data collection statistics are summarized in Table 3.
Although the nominal resolution for the three data sets recorded on a selenomethionine-substituted crystal was 1.63 Å, data extending to only 1.8 Å were employed for searching for Se sites using the program SHELX D (Sheldrick, Acta Cryst. A 64:112-122, 2008) Two fully occupied Se sites were located along with four partially occupied sites. The initial phases to 1.63 Å resolution were calculated and the density modifications were performed with the program SHELX E (Sheldrick, 2008 supra). A readily traceable electron density map resulted from the modification procedure. Automated model building was carried out using Arp/Warp (Perrakis, Nature Struct. Biol. 6:458-463, 1999), which traced 80% of main-chain structure. The resulting phases were combined with the high-resolution native data set (1.4 Å) and further manual modeling building was performed using COOT (Emsley and Cowtan, Acta Crystallographica Section D-Bilogical Crystallography 60:2126-2132, 2004) between the cycles of refinement using REFMAC5 (Murshudov et al., Acta Crystallographica Section D-Biological Crystallography 53:240-255, 1997). Analysis and validation of the structure were carried out with the assistance of the program MOLPROBITY (Lovell et al., Proteins-Structure Function and Genetics 50:437-450, 2003). The refinement statistics are summarized in Table 3:
Crystallization of K3 protein was carried out at room temperature. Crystallization screens were performed by using Mosquito (TTP LabTech), a Nano-drop crystallization robot, and 96-well screening kits (Qiagen). K1 could be crystallized but the crystals were not suitable for data collection. Bunches of tiny needle/plate crystals were observed for K3 from several conditions in the Classic and PEG suites (Qiagen) soon after the trays were set up (i.e. within ˜20 min). The conditions were optimized to 0.2 M calcium acetate, 26-28% PEG8000 and 0.1 M sodium cacodylate pH 6.5 to grow bigger crystals using the sitting drop vapor diffusion crystallization method. 2 μL of protein with a concentration of 15 mg/mL was mixed with 2 μL of solution from the reservoir. Crystals appeared after three days as bunches of plates. A suitable part of a plate with a single-crystal appearance was sectioned off and mounted on a loop. The crystal was subsequently flash-cooled in an N2 stream at 100 K using the mother liquor as cryo-protectant. Diffraction data were initially collected using an in-house X-ray source with a rotating anode x-ray generator (Rigaku RU200) with an image plate detector (Marresearch scanner 345 mm plate). Data were also measured on the beam line 3BM1, Australian Synchrotron, Melbourne, using an ADSC Quantum 210r CCD detector. Intensities were integrated and processed using the HKL2000 program (Otwinowski and Minor, 1997 supra). Solvent-content analysis indicated that the asymmetric unit contained four molecules with a Matthews coefficient of 2.22 Å3/Da (44.58% solvent content). The structure was solved using the molecular replacement method and the program Phaser (McCoy et al., J Appl Crystallogr 40:658-674, 2007) with the K2 structure (PDB entry 3KM5) as the search model. The program COOT (Emsley and Cowtan, 2004 supra) was used for further manual model building and cycles of refinement were performed by using REFMAC5 (Murshadov et al., 1997 supra).
The data reduction and refinement statistics are summarized in Table 3.
Kgp and RgpB were extracted from strain HG66 P. gingivalis and purified according to established protocols as previously reported (Potempa and Nguyen, Purification and characterization of gingipains In: Current protocols in Protein Science, Chapter 21:Unit 21.20, 2007). 250 μL Ni-NTA beads bound with 2.5 mg 6×His-K2 was equilibrated in buffer containing 200 mM Tris pH 7.6, 100 mM NaCl, 5 mM CaCl2, 0.02% NaN3 and 10 mM L-cysteine. 20 μL of Kgp (2.13 mg/ml) containing 0.1 mM leupeptin (an Rgp-specific inhibitor) was added to 250 μL of above buffer and subsequently mixed with the beads in a 1.5 mL microfuge tube. The tube was rotated at 37° C. for 6 hours. Near complete cleavage was confirmed by SDS-PAGE.
After cleavage, beads were washed with 1 mL of buffer containing 20 mM Tris pH 8.0 and 100 mM NaCl for 10 times to remove the gingipain and 6×His-tag was removed by incubating with 45 μL thrombin (1 μg/μL, Sigma) in 250 μL buffer of 20 mM Tris pH 8.0 and 100 mM NaCl overnight at room temperature. The de-tagged cleaved K2 was further purified by exclusion chromatography using a Superdex 75HR, 10/30 column (Amersham). The purified cleaved K2 was analyzed by electrophoresis on 16% w/v Tricine-SDS-PAGE to resolve the low molecular weight fragments. These were identified by N-terminal sequence analysis at the Australian Proteome Analysis Facility, Macquarie University, Sydney.
Preparation of Other Recombinant Domains within the Hemagglutinin of Kgp
The HA2 domain corresponding to the N-terminus of K2 (see
Analysis of protein fold stability in response to temperature was performed using the “Thermofluor” technique, which has been used as a drug discovery tool (Pantoliano et al., J Biomol Screen 6:429-440, 2001) and as a means of optimizing crystallization propensity (Ericsson et al., Anal Biochem 357:2890-298, 2006; Malawski et al., Protein Sci 15:2718-2728, 2006). Briefly, the protein of interest is incubated in the presence of SyproOrange (Invitrogen), a fluorescent dye which exhibits enhanced fluorescence when exposed to the hydrophobic residues normally buried in the interior of most natively folded proteins. Fluorescence is monitored as the temperature of the sample is increased. During a typical melting experiment fluorescence increases as the protein unfolds, then decreases as the unfolded protein molecules fall out of solution.
Melting experiments were performed in a 96-well plate format using a 7500 Fast RealTime PCR System (Applied Biosystems) in TAMRA filter mode. Protein (K1, K2 or K3) was diluted in 50 mM Tris (pH 7.5) and spiked with fluorescent dye such that a 20 μL aliquot contained 10 μg of protein and SyproOrange at a final concentration of 20×. An additional 5 μL of water or CaCl2 stock solution was added such that final CaCl2 concentrations of 0.00, 0.02, 0.20, 2.00, and 20.0 mM CaCl2 were achieved. Melting curves commenced at 25° C. and progressed to 95° C. at a rate of 45 sec/° C., with fluorescence readings taken every degree. Data were normalized for basal fluorescence after which each melt curve was expressed as a percentage of maximum fluorescence.
Sequence alignment of K1 and K3 reveals that they share 71% sequence identity. Homology modeling of K1 was performed using the K3 crystal structure as a template. The aligned K1 and K3 sequences and the K3 template was used as input for the comparative protein modeling software MODELLER (Sali and Blundell, 1993 supra) using the graphical user interface of Discovery Studio (DS v1.7, Accelrys, San Diego, Calif., USA). Variations in loop conformations at loops L2, L4 and L10 suggested by sequence alignments were incorporated into the model. The arginine from L10 was manually located at the conserved anchoring site and the calcium binding sites-I and -II incorporated into the model. This homology model for K1 was subsequently used in rigid body refinements of the K1 component in the models of K1K2 and K1K2K3 derived from SAXS data.
A complex of rHSA (Prospec, Rehovot, Israel) and hemin (Sigma) was prepared as previously described (Fanali et al., FEBS J 274:4491-4502, 2007). A stock solutions of hemin at 12 mM was prepared in 100 mM NaOH. A solution of rHSA with a concentration of 0.1 mM was prepared in 0.1 M sodium phosphate buffer pH 7.0. A solution mixture with a molar ratio of rHSA:hemin=1:1.2 of the complex had a light brown color and was stable at room temperature for 20 min. It was centrifuged for 10 min and a dark precipitate discarded. The resulting supernatant was used to purify the complex by gel filtration using a Superdex 200 HR 10/30 column in 1×PBS buffer pH 7.4.
Chemicals and Reagents.
Bovine serum albumin (BSA), L-cysteine, sodium dodecyl sulfate (SDS), N-α-tosyl-
Assay of Hemolytic Activity.
Blood was drawn from human donors into 0.1 M citrate anticoagulant. Erythrocytes were separated from platelet-rich plasma and the buffy coat by differential centrifugation at 150×g for 15 minutes. The erythrocytes were pelleted by centrifugation at 350×g and washed twice in PBS (pH 7.4) and resuspended to 1% (v/v) in PBS. Various concentrations of K2 up to 10,000 nM were added to the erythrocytes in a total volume of 200 μL and incubated at 25° C. or 37° C. After periods of incubation, the microtiter plate was centrifuged at 1000×g for 10 min and the supernatants (100 μL) transferred into a new microtiter plate. Hemoglobin release was determined spectrophotometrically using a microtitre plate reader (absorbance at 405 nm).
Inhibition of Anion Transport.
Washed erythrocytes were treated with 0.1 mM of the anion transport blocker 4-Acetamido-4′-isothiocyanato-2,2′-stilbenedisulfonic acid disodium salt hydrate (SITS; Sigma Pharmaceuticals) at 37° C. for 1 hour. After incubation, cells were washed several times with PBS to remove the inhibitor, and K2 polypeptide was then added to the erythrocytes at different concentrations and incubated at room temperature for 24 hours.
Proteolytic Treatment of Erythrocytes.
The capacity of RgpB to sensitize erythrocytes to the hemolytic effect of K2 was assessed by pre-incubating erythrocytes with 5 mM L-cysteine-activated RgpB at 4 or 20 nM for 30 minutes at 37° C., followed by a wash step to remove excess RgpB. Cell-bound RgpB were inhibited with the protease inhibitor TLCK prior to addition of K2. K2 polypeptide or control buffer were added to the pre-treated erythrocytes and incubated at room temperature for 48 hours. Hemoglobin released was then measured as described above.
Enzyme Activity Assays.
The amidolytic activity of the purified RgpB was confirmed with the chromogenic substrate GPR-pNA (1 mM final concentration). RgpB was pre-incubated in 50 mM Tris, 1 mM CaCl2, pH 7.5 (Tris buffer), containing 5 mM cysteine for 5 min at room temp. Enzyme and substrate were combined in a total volume of 200 μL Tris buffer and the rate of hydrolysis was measured at 37° C. within 1 hour on the basis of the increase in optical density at 405 nm, using a Bio-Rad Benchmark microplate reader.
Glycophorin A and Immunoblot Analysis.
Human glycophorin from blood type B negative which is predominantly glycophorin A, was purchased from Sigma (St. Louis, Mo.). Mouse monoclonal antibody specific for human glycophorin A (clone: GA-R2) was purchased from Becton Dickinson Inc. (Heidelberg, Germany).
Pre-activated gingipain was incubated with glycophorin A at a final enzyme to substrate (E/S) ratio of 1:100 (10 nM RgpA or Kgp with 1 mM glycophorin A) in the absence of serum. The reaction was then incubated at 37° C. for a time-course study. Hydrolysis was terminated at the indicated time with TLCK (2 mM final conc.). Aliquots were then resolved by 12% w/v SDS-PAGE under reducing and denaturing conditions and subjected to Immunoblot analysis. Immunoblot detection was performed using the primary mouse anti-human glycophorin A mAb (1:500 dilution) and the corresponding AP-conjugated rabbit anti-mouse mAb (1:1000). Membranes were washed five times in Tris-buffered saline-0.1% v/v Tween 20 between each step. Color was developed in a solution containing nitroblue tetrazolium chloride (1.65 mg) and 5-bromo-4-chloro-3-indolylphosphate p-toluidine salt (0.8 mg) in 10 mL of 100 mM Tris-HCl (pH 9.5).
Analysis of K2 (Li et al., 2010 supra) indicated the functional importance of the conformational state of the adhesin domains. For instance, poor binding of K2 to immobilized targets was observed. In the present analysis binding studies were performed using immobilized gingipain domains. Ninety six well ELISA plates were coated with K3, K2 or K1 polypeptide (0.4 g/well in PBS) and incubated overnight at 4 C. The wells were blocked with 100 L of 1% w/v skim milk in PBS for 1 hr. Haemoglobin (Hb) [Sigma] was added to the plates in various concentrations. Thereafter, anti-human Hb rabbit polyclonal antibody was added, followed by alkaline phosphatase conjugated goat anti-rabbit IgG. Alternatively, fibrinogen from human plasma (Sigma) was added to the coated plates at different levels. Thereafter, anti-fibrinogen mAb (FG-21, Sigma) was added, followed by alkaline phosphatase-conjugated rabbit anti-mouse IgG. The binding affinity between the polypeptides and rHSA or rHSA-heme was also detected by adding different levels of rHSA in PBS buffer or rHSA-heme in buffer containing 0.1 M heme to the coated plates. Thereafter, anti-HSA mAb (15C7, AbCam) was added, followed by alkaline phosphatase-conjugated rabbit anti-mouse IgG. The plates were washed with 0.05% v/v Tween 20 in PBS solution except for the rHSA-heme solution in the wells were washed with 0.1 M heme in Tween solution three times between each step. Color development was detected with phosphatase substrate. Data were fitted by non-linear regression using GraphPad Prism 4.0 software (GraphPad Inc., La Jolla, Calif., USA). Apparent Kd values were calculated from the fitted curves.
Loop 1 of K2 represents a unique characteristic for this particular adhesin domain. To probe the contribution of this loop to binding of mammalian proteins customized affinity purified rabbit antibodies to the antigenic sequence ETFESSTHGEAPAEC (SEQ ID NO:32) were prepared by GenScript Corp. This preparation was evaluated by pre-incubation of K3 or K2 at 10 μM/well in PBS with or without rabbit anti-HA2 polyclonal antibody at 5 μg/ml overnight at 4° C. The wells were then blocked with 100 μl of 1% w/v skim milk in PBS for 1 h. rHSA at various levels (1 to 100 μM) was added to the plates. Thereafter, anti-HSA mAb pre-absorbed with normal rabbit serum at a ratio of 1:1 was added, followed by alkaline phosphatase-conjugated rabbit anti-mouse IgG. Color development was detected with phosphatase substrate.
K1K2 and K1K2K3 were buffer-exchanged using a Superdex 75 (10/300) size-exclusion column in 150 mM NaCl, 10 mM β-mercaptoethanol, 10 mM Tris, pH 7.6. Both individual protein samples eluted as a single peak and the pooled peak fractions from the column were analyzed immediately using SAXS. A protein free fraction was used as an exact solvent blank for the SAXS experiments. SAXS data of I(q) vs q (q=(4π sin θ)/λ), 2θ is the scattering angle and the λ wavelength of the radiation; CuKα, 1.54 Å) were measured as essentially described in (Jeffries et al., Journal of Molecular Biology 377:1186-1199, 2008) at 15° C. over a period of 3 hr using a SAXSess (Anton Paar, Austria) line collimation instrument equipped with a CCD detector over a q-range of 0.010-0.37 Å−1 (K1K2) or 0.008-0.4 Å−1 (K1K2K3) and 10 mm integration width. The program SAXSquant 2.0 (Anton Paar, Austria) was used to subtract the scattering of the solvent blank from the proteins in solution to yield the scattering profiles from the protein molecules alone, while also including corrections for sample absorbance and detector sensitivity. The program GIFT (Bergmann et al., Journal of Applied Crystallography 33:1212-1216, 2000) was used to calculate the probable distribution of distances between atom pairs in real space (P(r) profiles) using an indirect Fourier transformation, that included a correction for beam geometry, from which the maximum dimension (Dmax), radius of gyration (Rg) and forward scattering intensity at zero angle (I(0)) of both K1K2 and K1K2K3 were determined. The smoothed I(q) vs q profile output from GIFT was used to apply the beam-geometry correction to the experimental data and all subsequent structural parameters and modeling as quoted in the text are derived from the K1K2 and K1K2K3 beam-geometry corrected datasets. This includes Guinier analysis, (analyzed in PRIMUS [Konarev et al., Journal of Applied Crystallography 36:1277-1282, 2003]), ab initio shape restoration using the program DAMMIF (Franke and Svergun, Journal of Applied Crystallography 42:342-346, 2009) and rigid-body modeling using BUNCH (Petoukhov and Svergun, Biophysical Journal 89:1237-1250, 2005). It must be noted that ab initio shape restoration was performed 10 independent times using the K1K2 and K1K2K3 GIFT outputs and the final solutions (average K1K2 fit=0.61; K1K2K3, χ=0.82) were aligned, averaged and volume corrected (Volkov and Svergun, Journal of Applied Crystallography 36:860-864, 2003) to produce the restored shape models. The normalized spatial discrepancy values of K1K2 and K1K2K3 were 0.66+/−0.01 and 1.0+/−0.02, respectively (Volkov and Svergun, 2003 supra). BUNCH refinement was repeated five independent times on both K1K2 and K1K2K3 datasets to derive the consensus ensembles that fit that data shown in
PDB Deposition Coordinates of K2 have been deposited in the Protein Data Bank (PDB ID Code: 3KM5). PDB deposition Coordinates of K3 have been deposited in the Protein Data Bank (PDB ID CODE: 3M1H). The atomic coordinates are also shown in
A bioinformatic analysis of the sequences of HA regions expressed on the surface of P. gingivalis supported the proposal that an alternative domain structure existed in the gingipains (see the Cleaved—Adhesin Family PF07675 in The Pfam protein families database, Finn et al., 2008 supra). The Cleaved_Adhesin 19 kDa domains K1, K2, and K3 or R1 and R2 defined herein are similar in sequence and share more than 30% sequence identity indicating structural homology (
In addition to these particular P. gingivalis proteins, genomic analyses indicate that homologous protein modules associated with the Cleaved_Adhesin domain family may be expressed in at least 7 other bacterial phyla including Flavobacterium and Proteobacterium species (see the Cleaved—Adhesin Family PF07675 in The Pfam protein families database, Finn et al., 2008 supra). A number of these hypothetical proteins have sequences that suggest a more complex domain structure that includes extra domains such as fibronectin type III (FNIII) and/or Meprin, A5, μ (MAM) domains. Such complex domain structures are consistent with putative roles in cell adhesin. Sequence features of the Cleaved_Adhesin domain family imply structural similarities exist with other related protein domain families and that it forms part of the galactose-binding domain-like superfamily (GBD CL0202: The Pfam protein families database, Finn et al., 2008 supra). The GBD superfamily is defined by a beta sandwich fold with a distinct β-barrel topology different from that found in immunoglobulin (Ig)-like and FNIII domains. Representatives of the superfamily include the MAM domain (Aricescu et al., Science 317:1217-1220, 2007), a number of the carbohydrate binding modules (CBMs) [Jamal-Talabani et al., 2004 supra, Bae et al., 2008 supra], and the ephrin receptor ligand binding domains (Ephrin_lbd) [Himanen et al., 2001 supra]. Many of the protein modules in these structurally related families are involved in cell adhesin that is mediated by specific protein-protein interactions, or by carbohydrate binding.
Recombinant 6×His-tagged K2 protein was expressed at a high level in E. coli and purified to a purity of more than 95% (as estimated on SDS-PAGE) by affinity and gel filtration chromatography. The protein migrates as a 23 kDa species on SDS-PAGE although the calculated molecular weight is 19.3 kDa (
Overall, the K2 domain has a ‘jelly-roll’ fold with eleven β-strands forming two anti-parallel β-sheets (
Two independent observations of the molecular structure of K2 are observed in the crystal (designated chains A and B) and they vary significantly only in their crystal packing arrangements and in interactions with additives such as glycerol. A number of intermolecular interactions result from the crystal packing, but there is no significant protein-protein interaction surfaces suggested by these arrangements. They involve residues in 6 β strands (β1, β2, β6, β9, β10, β11) and 7 loops, (L1, L2, L3, L4, L7, L8, L10) in chain A. Alternative loop conformations may be populated in solution or ligand complexes.
Gly1333 in the C-terminus is only present in chain A and Gly1334 is absent in both chain A and chain B. Two calcium (
With a diffraction resolution of 1.4 Å, the overall electron densities are very clear and strong except those for residues Gly1273-Lys1276 and Ser1284-Gly1289 in L8. Electron densities in these two fragments are so weak that only the main chain for these residues is able to be modeled in chain A and no mainchain model for residues Ala1287-Gly1289 in chain B is reported here. The fragment Gln1293-Val1295 in chain A and chain B are observed in different conformations. The residual electron densities for the fragment Gln1293-Val1295 in chain A indicate that there is at least one alternative conformation present in the crystal but this was not able to be modeled because of the weak residual densities, while in chain B the equivalent fragment has only one conformation with clear density. One glycerol (added as a cryo-protectant) and one water molecule were found to sit in a closed pocket formed by the fragments of Trp1197-Thr1199, Lys1291-Trp1296 and Tyr1322-Leu1324 only in chain B. With the hydrogen bond connections, these glycerol and water molecules are believed to have stabilized the conformation of fragment Gln1293-Val1295 in chain B. Observations of weaker densities in residues Gly1273-Lys1276 and Ser1284-Gly1289 may indicate that other conformers of loop L8 can be readily adopted in protein or ligand bound complexes formed by K2.
K2 is the first structure solved in the Cleaved_Adhesin family. An analysis of the sequences of those known to be associated with this family suggests that the structural differences are most likely to be found primarily in the loop regions. A comparison of the sequences of the closely related K1 and K3 domains (71% sequence identity in strain W83) with K2 (36% and 33% identity respectively) indicates that loops L3 and L8 are shorter in these particular Cleaved_Adhesin domains (
In order to understand more about the structure and its membership in the galactose-binding domain-like superfamily, a search for structural resemblances and common structural cores found in K2 was performed by the program DALI (Holm AND Park, Bioinformatics 16:566-567, 2000). The list of the closest structural homologues includes the MAM domain found in human receptor-type tyrosine-protein phosphatases (RPTPμ MAM domain), a protein adhesin, followed by ephrin type-A/B receptors EPHA2, EPHA4, EPHB2 and EPHB4 and a number of carbohydrate binding modules (sorted by the Z score, which represents the strength of structure similarity). The superimpositions of K2 with a number of these structural homologues are shown in
The differences between K2 and these homologs are mainly in the loop structures at the ‘head end’ of the β-barrels. Some of these loops from K2, MAM domain and ephrinB2-binding domain are partially super imposable but overall their conformations are quite different in K2 (
In comparing the ‘head ends’ of the β-barrels of K2 and CBM domains, the loops are shorter in CBM domains and there is no equivalent to the longest loop K2-L8 in the CBM structures (
To examine carbohydrate binding by K2 a selection of glycans was absorbed to nitrocellulose membranes and probed with recombinant K2 as described in
HA2 (also known as Kgp15 or Rgp15 or HbR) has been assigned as a heme binding acceptor relating to binding capacity for hemin and hemoglobin. From sequence analysis, K2 extends for 44 residues beyond the C-terminal of HA2. In the K2 structure, the 44 residues form β-strands 9, 10 and 11 which are intrinsically part of the two anti-parallel β-sheets (
Freshly isolated human Blood Group A and O erythrocytes were studied. Hemolysis of red cells induced by K2 was concentration- and time-dependent. K2 was effective in a range of 10 to 5000 nM with 50% hemolysis observed at ˜250 nM (
As the Kgp cleavage sites in K2 at Lys 1291 and Lys 1276 are located within loop L8, the data provide evidence that cleavage or truncation specifically affecting this loop critically removes hemolytic capacity. For hemolytically active K2 evidence that the 30 residue surface loop L8 is flexible is not inconsistent with involvement in a specific binding function. Accordingly, proteolytic processing of the loop (at Lys 1291 and perhaps Lys 1276) would readily modify the conformational state of L8 leading to loss of capacity to engage in intermolecular associations necessary for hemolytic action.
The effect of the anion transport inhibitor SITS on hemolysis of erythrocytes induced by the K2 domain was examined (
The potential for proteolytic activity of the gingipains acting cooperatively with K2 to enhance hemolytic activity was analyzed. This was investigated to develop the findings of Chu et al., 1991 supra indicating that proteinase inhibitors effectively blocked the hemolytic action of P. gingivalis. RgpB was selected for initial studies as this gingipain lacks the predicted domains of the region of RgpA. When 5 mM L-cysteine activated RgpB at 4 or 20 nM was incubated with erythrocytes there was only a low level of hemoglobin release (
Using standard ELISA binding assays (O'Brien et al., J Immunol 75:3980-3989, 2005), the binding of gingipain domains to fibrinogen and fibronectin was examined. No binding of K2 or cleaved K2 could be detected while high affinity binding of Kgp to both fibrinogen and fibronectin was detected as previously reported (O'Brien et al., 2005 supra). In this study the authors provisionally mapped fibrinogen and fibronectin binding to sites located beyond C-terminus of K2. Accordingly, the lack of recognition by K2 of these substrates is predicted.
As the N-terminal fragment of cleaved K2 corresponds to the putative hemoglobin/heme receptor (HbR or HA2) (
The Cleaved_Adhesin Domain modeling confirms a relationship to the galactose-binding domain (GBD) superfamily. These domains are based on bacterial genomic data of a number of expressed proteins and likely to be acting in concert with other adhesin modules such as fibronectin III and MAM domains. These relationships lead to the consideration of a number of specific roles in which these proteins and their domains may be involved. The structural models of the HA protein regions expressed on the surface of P. gingivalis have previously been based on the analysis of proteolytic fragments observed after extraction from the cell. Analysis of the in-vitro biochemical activities of these fragments has suggested a number of different possible functions for the HA regions of gingipains and Hag proteins. The determination of the K2 structure and the confirmation that an integral folded state exists within a novel boundary of the polyprotein suggests that an alternative domain model represents the functional states of these proteins. In the case of K2, it is shown that the structural domain defined by these boundaries facilitates a hemolytic function consistent with that previously associated with the outer membrane gingipain complexes (Lewis et al., 1999 supra). This is an example of the use of the alternative domain model in understanding the exact biological and physiological roles of these domains in this organism. Knowing these domain boundaries and by inference, the domain boundaries of other components of HA regions in gingipains and Hag proteins, enables the identification of agents which specifically target these domains and to inhibit protein activity.
The present disclosure defines the domain sub-structure (
The link to function is based research involving X-ray crystallography (
The Docking program, Haddock, is used to predict the site of interaction of K3 with the trisaccharide of the blood group A antigen. It is proposed that the site of interaction is amino acid residues 34, 35, 37, 38, 39, 50, 134 and 135 which correspond to ProPro GlyGlySer Asn GlyThr, respectively. This target is used for designing sugar mimetics in a number of domains including K1 and K3 and R1 and A1, A2, A4, A6, A8 and A10.
Monoclonal antibodies (Mabs) 5A1 and 2B2 were raised against a gingipain preparation. 5A1 was partially mapped to a PDNYL sequence partially buried on K2. This antibody also reacts with this sequence in HA1 of RgpA and Kgp39. 2B2 recognizes a determination, on HA1/HA3 of Kgp39. A rabbit antibody is also raised to a peptide sequence that is entirely on the surface of K2.
Multiple sequence alignment modeling was used to identify homologous Cleaved_Adhesin domains in other proteins. In particular, the K1 sequence was aligned with the sequence of the K3 domain (
The crystal structure of the W83 Kgp K2 module (PDB code: 3KM5) shares a highly conserved sequence with modules found in each of the Kgp, RgpA and HagA proteins expressed by strains of P. gingivalis (Li et al., 2010 supra). This recombinant protein module was shown to be haemolytic in vitro. In this disclosure provides the crystal structure of the K3 module of W83 Kgp at a resolution of 1.56 Å. K3 folds into a similar β-barrel module as K2 and it is also stabilised by two Ca2+ ions. This indicates that these HA region modules share some functional roles. Given the sequence identity of 71% between K3 and K1, the structure of the K1 module in Kgp can now be predicted with confidence. this disclosure shows that the HA region of Kgp W83 is composed of three tandem repeats of homologous protein modules. A recombinant construct containing these three modules was shown by small-angle X-ray scattering (SAXS) to be multi-globular and with each module being only loosely associated in solution. The variable loop regions of each of the modules are solvent accessible in the SAXS-derived molecular models. Of note, each of the HA modules presents loops which form significantly different molecular surfaces implying different possible adhesin functions, while some areas of the surface are structurally conserved and may act synergistically in common functional roles.
The K3 module, as crystallized, is composed of 178 residues with a molecular weight of 19 kDa (residues Ala1427-Gly1602 of Kgp W83 with glycine and serine attached to the N-terminus). While K3 has the same principal structural feature of the β-jelly roll-barrel observed in K2 (
In this crystal structure, nine Na+ ions in total have been modeled on the surfaces of the four independently determined K3 molecules (designated chains A, B, C and D) and it is likely that these ion bound states are at least partly dependent upon the particular crystal packing arrangement. With a resolution of 1.56 Å, the calculated electron densities derived from the refined K3 structure are generally consistent with a single molecular model except for the N-terminal half of L10, Leu1544-Pro1553. Of the four K3 molecules in the asymmetry unit, only chain B and D have continuous observed main chain electron densities in this region with weak side chain densities for residues Leu1544-Lys1547. The electron densities are missing for residues Thr1551-Ala1552 in chain A and Ala1546-Pro1553 in chain C. The weak, variable and missing electron densities indicate that the N-terminal half of L10 is a flexible region and that the observed conformations of the residues in this loop are at least partly derived from the specific crystal packing arrangements.
A stabilizing feature of the more ordered C-terminal fragment of L10 is noteworthy. Sequence alignments do not match the structural alignment derived from a comparison of the crystal structures of K3 and K2 at this location. When the three dimensional structures are superimposed however, Arg1557 of L10 in K3 is located in an almost identical position, conformation and interacting environment, as observed for Arg1280 of L8 in K2 (
The K3 and K2 domains of Kgp from P. gingivalis W83 have 34% sequence identity (Li et al., 2010 SUPRA). Superimposition of K3 and K2 structures using the program DALI (Hasegawa and Holm, Curr Opin Struct Biol 19:341-348, 2009) shows that 158 Cα atoms can be aligned with an rmsd of 1.7 Å and Z score of 22.6. The aligned residues mainly locate to the β-strands and to the short loops on one end of the barrels (
Minor differences are observed between the two structures; the K3-barrel comprises ten β-strands in two β-sheets while K2 has eleven β-strands in the β-barrel. There is no equivalent in K3 to the four residue strand β3 in K2 as there is small difference in local backbone conformation. K3 presents an extended loop L2 (residues Ala1447-Cys1473) and in total corresponding in K2 to the residues of L2 (Ala1179-Trp1187), β3 (Leu1188-Ser1191) and L3 (Ser1192-Ser1204). Two additional β-strands in K3 (β4 and β5), linked by only two H-bonds, form an independent and very small anti-parallel β-sheet adjacent to loop L10 at one end of the β-barrel. This is part of the U-shaped feature (L3-β4-L4-β5-L5) in K3 which in K2 is reduced to one shorter loop (L4) [
Major differences between the two structures exist only in the extensive loop regions at one end of the β-barrel. The long loops L2 and L10 in K3, and L1, L3 and L8 in K2, present very different conformations to possible interacting partners and this is also reflected in the variation in the residues which form these loop regions (
The Ca2+ ions in K3 and K2 superimpose to almost equivalent structural positions (
The role of Ca2+ in stabilising the observed folded forms of the K1, K2 and K3 adhesin modules in Kgp was investigated. The ThermoFluor technique was used to follow K1, K2 and K3 melting in response to temperature and the presence of Ca2+. Temperature-induced unfolding is accompanied by an increase in fluorescence in response to a fluorophore gaining access to the core hydrophobic residues. Only the K1 preparations used here contain additional non-bound Ca2+ at <0.5 mM post-dialysis. The melting point temperatures were observed as K3>K2>K1. K1 and K2 samples were both significantly stabilised by the addition of Ca2+; however, K1 shows the greatest enhancement of stability in the presence of Ca2+ (
Haemolytic activity was determined as described below.
Trizma base, tris-hydrochloride (Tris-HCl) and Tween 20 were purchased from Sigma (St. Louis, Mo.). Phosphate buffered saline (PBS) was purchased from Oxoid (Basingstoke, United Kingdom). Blood was drawn from human donors into 0.1 M citrate anticoagulant. Erythrocytes were separated from platelet-rich plasma and the buffy coat by differential centrifugation at 150×g for 15 min. The erythrocytes were pelleted by centrifugation at 350×g and washed twice in PBS pH 7.4 and resuspended to 1% volume/volume in PBS. Various concentrations of K2 up to 10,000 nM were added to the erythrocytes in a total volume of 200 μL and incubated at 25° C. or 37° C. After periods of incubation, the microtiter plate was centrifuged at 1000×g for 10 min and the supernatants (100 μL) transferred into a new microtiter plate. Haemoglobin release was determined spectrophotometrically using a microtitre plate reader (absorbance at 405 nm, the peak absorbance in the Soret region).
Freshly isolated human Blood Group A and O erythrocytes were studied. Haemolysis of red cells induced by K3 was concentration- and time-dependent. K3 was effective in a range of 10 to 5000 nM with 50% haemolysis observed at ˜250 nM (
An investigation of K3 ligand binding involved dot blot arrays to probe the binding of 6×His tagged K3 to target proteins and glycans immobilized on nitrocellulose. Data indicated that the tagged K3 bound strongly to human serum albumin (HSA) and fibrinogen. Relatively strong binding was also observed for bovine maxillary mucin and hyaluronan while only weak binding was detected for the other glycans tested.
The apparent Kd values determined by ELISA for titrations of haemoglobin binding to immobilized adhesin domains were 154 nM for K3 polypeptide, 80 nM for K2 polypeptide and 360 nM for K1 polypeptide (
Small-angle X-ray scattering (SAXS) data were collected from solutions of K1K2 and K1K2K3. These data are sensitive to the size and shape of particles in solution and were ultimately used to probe the domain organization of both proteins. Guinier analysis (Guinier, Comptes Rendus Hebdomadaires Des Seances De L Academie Des Science 206:1374-1376, 1938) of the K1K2 and K1K2K3 data at very low-q shows excellent linear correlations (R2˜0.995), consistent with samples that are free of aggregation or significant interparticle interference and, when combined with molecular weight determinations derived from the forward scattering intensity at zero angle (I(0)), indicate that K1K2 and K1K2K3 exist as systems of monodisperse monomers in solution. Under these conditions, the real-space probable distribution (P(r)) of atom pair-distances (r) within the proteins were calculated via indirect Fourier transformation of the data (Bergmann et al., 2000 supra), from which the maximum dimension (Dmax) and radius of gyration (Rg) were determined. Overall, K1K2K3 has a longer maximum dimension (Dmax, ˜150 Å) and has a larger Rg (˜45 Å) compared to K1K2 (Dmax, ˜95 Å; Rg, ˜30 Å) suggesting that the mass representing K3 extends from K1K2.
The shape of the atom-pair distance distributions of K1K2 and K1K2K3 display characteristics of modular proteins that have discrete, well defined domains (as opposed to compact globular particles or extended rod-shapes) indicated by the “humps” in the distributions at mid-range vector lengths (˜50-80 Å) that arise due to scattering from ‘between-domain’ atom-pair distances. Ab initio shape restoration from the data (Franke and Svergun, 2009 supra) reveals that K1K2 is a ‘double-lobed’ protein, with each lobe having an approximate volume as a single K-domain (˜22-24 000 Å3). The two lobes of K1K2 are spatially positioned in tandem next to each other and this K1K2 configuration is preserved in K1K2K3 that adopts an overall “y” shaped conformation in solution. Further refinement against the SAXS data of the domain orientations within the K1K2 and K1K2K3 molecular envelopes was performed using BUNCH (Petoukhov and Svergun, 2005 supra) that employed the crystal structures of K2, K3 and a homology model of K1 as independent rigid bodies, while also incorporating dummy-atoms to represent the mass of the linker regions of unknown structure between K1-K2 and K2-K3. The rigid body refinements generated K1K2 and K1K2K3 models that fit to the data very well (K1K2, χ2=0.51-0.66; K1K2K3 χ2=0.74-0.86) and the overall “y” shape of the K1K2K3 atomic representations correspond to the shapes generated in the ab initio models.
Due to the near mass equivalency of K1 and K2, it is difficult to determine from the SAXS data the exact orientation of K1 or K2 with respect to K3 in the y-shape other than that the K1 and K2 modules comprise the two arms at the top of they and the K3 domain is positioned at the end of an extended ‘tail’ which is composed of a 93 amino acid linker between K2 and K3. Because of steric constraints imposed by the location of the N- and C-termini of each of the modules (that enter and exit on the same end of their respective -barrels—see
The structural core of the adhesin modules K2 and K3 are homologous but there are significant differences in the associated -barrel end loop regions and minor differences on the flanks of the ends of the barrel. Other adhesin modules in P. gingivalis HA regions (such as K1, R1, R2 and A2-10) as identified by sequence alignment and significant identities (>70% to either K2 or K3), are by definition, homologues. The two crystal structures, when combined with multiple sequence alignments of the other modules enables structural features of the whole domain family to be predicted. These data suggest that in the extensive loop regions at the “active” end of the β-barrels there will be found a spectrum of similarities and differences in this adhesin family. L8 in K2 has previously been linked to function by a specific proteolytic cleavage of two lysines in L8 by Kgp which arrests the haemolytic and binding activities of this module. Surprisingly, despite no obvious sequence correspondence with L8 of K2, the structure of K3 reveals that the “equivalent” loop L10 does in fact partially mimic K2. In particular, the arginine anchoring site appears to be conserved and it is proposed that in both K2 and K3 the overall conformations of L8 and L10, respectively are at least partly determined by this anchoring. Sequence, alignments imply that the same anchoring site may also be found in the stabilization of the overall loop conformations present in the K1 module. This suggests that rather than a direct role in haemolysis these particular loops (L8 in K2 and L10 in K3) associate to fix conformations of other associated loops in modules K2 and K3 but that these associated loops differ in K1, which is not haemolytic.
Comparing the protein sequences of other less similar putative domains with K2 and K3 (such A 1 and K3* with <35% sequence identity), it is predicted, for example K3*, found in Kgp of strain 381, will possess a slightly different surface feature with a, longer L2 but a substantially shorter L10 when compared to K3. As the sequences of 381 Kgp and W83 Kgp only vary significantly in the K3*/K3 domain regions, this is a structural feature that might explain strain specific functional differences.
In the K2 structure, Gly1273-Lys1276 and Ser1284-Gly1289 of L8 have very weak electron densities (Li et al., 2010 supra) and equally, the electron densities in the corresponding region in the K3 structure, Ala1546-Pro1553 in L10 in chain C are not observed. Weak or missing densities in high resolution crystal structures often indicates that multiple/flexible or disordered states exist in solution, and in some cases such flexibility may be related to a functionally active binding site. Interestingly, the two flexible regions of K2 and K3 are located at the same structural position and both have charged residues in their sequences, indicating they might be the sites for a similar binding function.
Bound calcium contributes to the stability of the folded states of these adhesin modules and is a general feature of the galatose-binding domain-like (GBD) superfamily. Comparisons of the K2 and K3 structures with their closest known structural homologues in the GBD superfamily, such as the MAM domain of human receptor-type tyrosine-protein phosphatases, ephrin receptors, a number of carbohydrate binding modules (CBMs) [Li et al., 2010 supra], and modules found in the sub-repeats of reelin (Yasui et al., Structure 18:320-331, 2010) reveal that Ca2+ binding site-I is widely conserved. Most interestingly, the Asp acid residue in Ca2+ binding site-I that corresponds to Asp1595 in K3, located at the adjacent to the C-terminus of β-barrel core, is found in an equivalent position in all of these homologues. A Glu residue from site I that corresponds to Glu1435 in K3, is also conserved in most of the CBMs. Ca2+ binding is a common feature for many domains with a β-sandwich folding topology and while many of the GBD structural superfamily share only the site-I Ca2+, other secondary cation binding sites have been reported. For example, CBM36 Xylanase (PDB entry lux7) has a second bound Ca2+ which mediates the binding of xylotriose ligand (Jamal-Talabani et al., 2004 supra). However, structural superimposition of CBM36 and K2 reveals that this different Ca2+ binding site in CBM36 does not superimpose onto Ca2+ binding site-II (Li et al., 2010 supra).
The in vitro binding properties of recombinant K1, K2 and K3 modules with putative ligands revealed similarities and variations reflecting observed structural differences particularly those found in the extensive loop regions. While apparent binding affinities to haemoglobin and fibrinogen were comparable in each of the three modules and being consistent with equivalences in folded structure and sequence, K1 binding to human serum albumin was not significant. The enhanced binding of heme-albumin compared with albumin is sufficient to facilitate selective uptake of heme-albumin from inflammatory exudate. That is, the organism has a demonstrated capacity to bind albumin that has scavenged heme, particularly heme released within the proximity of the lesion of periodontitis. This provides a further mechanism for uptake of essential heme by the gingipains.
The putative binding pockets observed in K3 (and predicted in K1) are not observed in the K2 crystal structure. These binding data indicate that there are likely to be specific structural differences between the K1 and K3 modules. Such a difference is likely to be found in the variable loops of these modules.
Both K2 and K3 have been found to possess an ability to induce haemolysis in a dose-dependent manner but with an unknown mechanism. Previous work on K2 suggested a link to anion transport in erythrocytes and the role of K2 loop L8 in this process (Li et al., 2010 supra). In the structure of K3, the conformation of the equivalent loop, L10, is significantly different but is anchored by an observed equivalent arginine binding site formed near the surface of conserved but non-aligned residues in the extensive loop region. This conserved structural motif (which is not predicted by the sequence alignment of these two loops) is unlikely to be the only structural determinant for any haemolytic process. This is because sequence alignment predicts that this structural motif may also exist in the non-haemolytic K1. The information presented here indicates that observed binding properties and haemolytic activities of these modules is dependent on specific features of the loop regions and that anchoring of the largest loop (L8 in K2 and L10 in K3/K1) which extensively covers one end of the barrel structure determines the conformational integrity and/or the surface structure of adjacent ligand binding sites.
SAXS-derived models of the K1K2K3 protein support the proposal that the HA region of Kgp is composed principally of three globular protein modules with dimensions corresponding to those observed in the crystal structures of K2 and K3 and the associated homology model of K1. The HA region of RgpA contains two modules termed R1 and R2 with close homology to K1 and K2 of Kgp. Both the HA regions of Kgp and RgpAs also include a sequence related ˜150 residue fragment C-terminal to the protease domain. The significant sequence homologies found in these fragments suggest the presence of another type of protein module of unknown structure and function (designated by databases as: Pfam entry. DUF2436 and InterPro entry IPR018832) within the HA regions of gingipains. This indicates that the gingipains are composed of protease domains, tandem repeats of cleaved-adhesin modules, combined with a third type of domain/region (DUF2436/IPRO18832-like) of unknown structure and function.
The SAXS data clearly demonstrate, that the three adhesin modules of the HA region of Kgp do not interact to form globular dimers or trimers and that the extensive loop regions in each loosely associated module are accessible to bind ligands.
Those skilled in the art will appreciate that the disclosure herein is susceptible to variations and modifications other than those specifically described. It is to be understood that the disclosure includes all such variations and modifications. The disclosure also includes all of the steps, features, compositions and compounds referred to or indicated in this specification, individually or collectively, and any and all combinations of any two or more of said steps or features.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2010900571 | Feb 2010 | AU | national |
| 2010900887 | Feb 2010 | AU | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/AU2011/000153 | 2/11/2011 | WO | 00 | 11/29/2012 |
