Expression of processed recombinant lactoferrin and lactoferrin polypeptide fragments from a fusion product in Aspergillus

FIELD OF THE INVENTION
The present invention relates generally to the field of iron-binding glycoproteins and related polypeptides, namely lactoferrins. More specifically, the present invention relates to the recombinant production of various lactoferrins and lactoferrin polypeptide fragments in Aspergillus, especially Aspergillus awamori, niger and oryzae.
BACKGROUND DISCLOSURES
In co-pending patent application U.S. Ser. No. 08/145,681, the cDNA sequences for human lactoferrin were disclosed. Additionally, in the same co-pending patent application U.S. Ser. No. 08/145,681, the cDNA sequences for human lactoferrin were used to produce human lactoferrin in a variety of different organisms, including various fungi, such as Saccharomyces cerevisiae, Aspergillus nidulens, and Aspergillus oryzae.
DESCRIPTION OF THE PRIOR ART
Lactoferrin (LF) is an iron-binding glycoprotein found in milk and other secretions and body fluids. LF is a member of the transferrin family and is involved in iron binding and delivery in mammals.
LF was originally discovered in milk where it can be secreted at levels up to 7 grams/liter in colostrum. Since that original discovery, LF has been detected in other secreted fluids of humans and other mammals. Those fluids include tears, saliva and mucosal secretions and also in the secondary granules of polymorphonuclear leukocytes.
LF is a 78 kilodalton (kDa) glycoprotein having a bilobal structure with a high degree of homology between the C and N terminal halves which is evident in both the amino acid sequence and the three dimensional structure levels. Each of these lobes can reversibly bind one ferric iron with high affinity and with the concomitant binding of bicarbonate. The biological functions of lactoferrin include static and cidal effects against microbial pathogens, transport of iron, promotion of cell growth, regulation of immune cell function and inflammatory response, and regulation of myelopoiesis. It has been found that the deglycosylated protein retains all biological functions of native LF.
The bactericidal domain from lactoferrin has a broad spectrum of antimicrobial action. Bellamy, W. M. et al., J. App. Bact. 73, 472-479 (1992). Although Bellamy et al. report that bovine lactoferrin isolated from milk can provide commercial quantities of the bovine polypeptide by pepsin digestion, the materials used in both studies had a maximum purity of 95%. Bellamy, et al. do not provide information for the large scale production of synthetic human or bovine lactoferrin or lactoferrin polypeptides. Neither does Bellamy et al. discuss methods which provide the ability to produce peptides that are not available by enzyme digestion.
Filamentous fungi have been employed as hosts in the industrial production of extracellular glycoproteins. Certain industrial strains are capable of secreting gram quantities of these proteins. In addition, filamentous fungi are able to correctly perform post-translational modifications of eukaryotic proteins and many proteins have U.S. Food and Drug Administration approval. Furthermore, large scale fermentation technology and downstream processing experience is available. However, there have been reports that lactoferrin is toxic to certain fungi (Valenti, et al, FEMS Microbiology Letters, 33:271-275 (1986); Epstein, et al, Reviews of Infectious Diseases, 6:96-106 (1984); Soukka, et al, FEMS Microbiology Letters, 90:223-228 (1992)) and consequently, workers have not employed fungi universally, particularly for production of lactoferrins.
Production of lactoferrins in filamentous fungi, particularly, Aspergillus, was first reported by the present inventors (Ward, et al, Gene, 122:219-223 (1992); Ward, et al., Biotechnology, 10:784-789 (1992); Conneely et al., Production of Recombinant Human Lactoferrin, PCT/US 93/22348, International Application Number PCT/US93/03614, having a priority date of Apr. 24, 1992 and published on Nov. 11, 1993; and Conneely, et al., U.S. Ser. No. 08/250,308 filed May 27, 1994, which is a continuing application of U.S. Ser. No. 07/873,304, filed Apr. 24, 1992, now abandoned, all of which are incorporated herein by reference). However, while these processes were a significant breakthrough, they have been limited in their ability to effectively produce large commercial quantities of lactoferrin.
Currently, there is a need for a more efficient and economical way to produce LF, either human, bovine, or porcine, in addition to a way to produce lactoferrin polypeptides. Consequently, there is also a need for the development of an efficient and commercial method for the production of human lactoferrin for nutritional and therapeutic applications and for further investigation into its mechanism of action. The subject invention satisfies this need by providing the production of lactoferrins and lactoferrin polypeptide fragments using the host cells Aspergillus in connection with novel vector constructs and especially methods of producing lactoferrins in Aspergillus host cells, which enables them to produce commercial amounts of recombinant lactoferrins and lactoferrin polypeptide fragments.
SUMMARY OF THE INVENTION
The subject invention provides for the production of lactoferrins and lactoferrin polypeptide fragments using the host cells Aspergillus in combination with novel plasmid constructs. More specifically, the subject invention provides novel vector constructs capable of producing lactoferrins and lactoferrin polypeptide fragments in Aspergillus host cells. More particularly, the subject invention provides for novel plasmid constructs suitable for use with Aspergillus and especially Aspergillus awamori, niger and oryzae host cells, which enables them to produce large amounts of recombinant lactoferrins and lactoferrin polypeptide fragments.
The subject invention also provides for a novel expression plasmid vector construct which enables the production of lactoferrin and lactoferrin polypeptide fragments. The plasmid vector constructs contain two important components which provide such high levels of lactoferrin to be produced. In addition to a promoter, cDNA coding for protein of choice, a signal sequence, transcription termination sequence and a selectable marker, the plasmid vector construct additionally contains (a) 5' half of a highly expressed endogenous gene whose product is secreted from the Aspergillus cell, and (b) a linker sequence whereby there is an endogenous proteolytic enzyme for the linker sequence. The product of this novel plasmid vector construct is a fusion protein comprised of half of the highly expressed gene fused to lactoferrin or lactoferrin polypeptide fragment. The fusion protein thereafter is processed by an endogenous proteolytic enzyme which is preferably specific for the Kex2 peptidase clevage site. For example, if the glucoamylase promoter from A. awamori is used, the vector would also contain the 5' half of the A. awamori glucoamylase gene. The lactoferrin produced would be fused to one-half of the glucoamylase gene and would then be processed by an endogenous A. awamori proteolytic enzyme which is specific for the Kex2 peptidase cleavage site. As another example, if the glucoamylase promoter from A. niger is used, the vector would also contain the 5' half of the A. niger glucoamylase gene. The fusion product produced by the vector construct (LF fused to one half of glucoamylase gene) would then be processed by an A. niger endogenous proteolytic enzyme specific for the Kex2 peptidase cleavage site releasing the desired lactoferrin protein or LF polypeptide fragment. Also, if A. oryzae cells were to be used, the vector construct would contain the A. oryzae promoter from the .alpha.-amylase gene and a portion of the A. Oryzae .alpha.-amylase gene. The vector would be used to transform A. oryzae cells and the fused product (LF fused to half of the amylase gene) would be processed by an A. oryzae endogenous proteolytic enzyme specific for the Kex 2 peptidase cleavage site yielding the desired LF or LF polypeptide fragment.
Thus, the subject invention provides a novel vector plasmid construct for producing LF or LF polypeptide fragments in commercial quantities in any strain of Aspergillus.
Another embodiment of the subject invention comprises the following components operably linked from 5' to 3' to form an expression plasmid vector:
(a) a promoter;
(b) a signal sequence;
(c) 5' portion of a highly expressed endogenous gene whose product is secreted from Aspergillus cells (i.e. glucoamylase gene);
(d) a linker sequence; and
(e) a nucleotide sequence corresponding to the desired lactoferrin or lactoferrin polypeptide fragment.
The above DNA sequences (a) through (e) are then cloned together to form a plasmid. The resulting expression plasmid is used to transform Aspergillus cells which will express the lactoferrin protein or lactoferrin polypeptide fragment (corresponding to the lactoferrin nucleotide sequence inserted into the expression plasmid) fused to one half of the highly expressed endogenous gene, for example, the glucoamylase gene. The LF or LF polypeptide fragment is processed by an endogenous proteolytic enzyme specific for the Kex2 peptidase cleavage site.
Another embodiment of the claimed invention is a process for producing lactoferrin which comprises culturing a transformed Aspergillus fungal cell containing a recombinant plasmid, wherein said plasmid comprises a nucleotide sequence which codes for lactoferrin proteins or lactoferrin polypeptide fragments, wherein said transformed Aspergillus fungal cells are cultured in a suitable nutrient medium until lactoferrin protein is formed as a fusion product and then processed via an endogenous proteolytic enzyme specific for Kex2 peptidase cleavage site, wherein said processed lactoferrin is secreted into the nutrient medium and wherein said lactoferrin is isolated or recovered from the nutrient medium.
The present invention is further defined in that the above mentioned plasmid vector further comprises a promoter, a signal sequence, a 5' portion of the glucoamylase gene, a linker sequence, a transcription termination sequence, and a selectable marker gene. For the purpose of this invention, "linker sequence" and "protease recognition sequence" are used interchangeably.
This expression vector is further defined wherein the promoter which is selected from the genes of the group consisting of alcohol dehydrogenase, .alpha.-amylase, glucoamylase, and benA and wherein the promoter is further defined to be from A. awamori glucoamylase gene.
The above described process is further defined wherein said promoter is from the glucoamylase gene, wherein said promoter is from the glucoamylase gene of A. awamori and wherein the signal sequence is from the A. awamori glucoamylase gene. This process is further defined wherein the above described signal sequence further comprises a 5' portion of the glucoamylase gene that is from A. awamori.
The above described process can be further defined wherein said promoter is derived from the glucoamylase gene, wherein said promoter is from the glucoamylase gene of A. niger and the signal sequence is from the A. niger glucoamylase gene. This process is further defined wherein the above described signal sequence further comprises a 5' portion of the glucoamylase gene that is from A. niger.
The above described process is still further defined wherein said promoter is from the .alpha.-amylase gene, wherein said promoter is from the a-amylase gene of A. oryzae and wherein the cDNA sequence corresponding to the signal sequence is from the A. oryzae a-amylase gene. This process is further defined wherein the above described signal sequence further comprises a 5' portion of the .alpha.-amylase gene that is from A. oryzae.
The above described process is further defined wherein the linker sequence is a peptidase recognition sequence. This invention is yet further defined wherein the linker sequence encodes the Kex2 peptidase recognition sequence. For the purpose of this invention, Kex2 peptidase recognition sequence and Kex2 peptidase cleavage site are the same.
The above described process is further defined wherein the transcription termination sequence is selected from the genes of the group consisting of alpha-amylase, glucoamylase, alcohol debydrogenase and benA. This invention is yet further defined in that the transcription termination sequence is from the glucoamylase gene and wherein the transcription termination sequence is from the glucoamylase gene of A. niger.
The above described process is further defined wherein the selectable marker gene is selected from the genes of the group consisting of pyr4, pyrG, amdS, argB, trpC, and phleomycin resistance. This process is yet further defined in that the selectable marker is from the phleomycin resistance gene.
This invention is further defined wherein the lactoferrin protein or lactoferrin polypeptide fragment is human, porcine or bovine lactoferrin protein. The invention is further defined and wherein any lactoferrin product has been deglycosylated.
Another embodiment of the present invention is a plasmid which consists essentially of DNA encoding the amino acids of a human lactoferrin and a plasmid vector for the expression of the DNA in the cell wherein said plasmid is used for expressing the DNA of a human lactoferrin in Aspergillus awamori fungal cells. A particular preferred plasmid is defined as one having the characteristics of ATCC Accession Number 74290 and designated Awa LF 24-1 wherein Awa LF 24-1 is Aspergillus awamori transformed with expression plasmid pPLF-19 containing DNA encoding human lactoferrin, i.e., Seq. I.D. Listing No. 1 of U.S. Ser. No. 08/445,681, the latter of which is incorporated herein by reference. Another embodiment of this invention is Aspergillus awamori fungal cells containing the above described plasmid.
Yet a specific embodiment of the present invention is a process comprising culturing a transformed Aspergillus awamori, niger and oryzae fungal cell containing a recombinant plasmid, wherein said plasmid comprises a plasmid vector containing:
(a) a promoter from the A. awamori glucoamylase gene;
(b) a signal sequence from the A. awamori glucoamylase gene; a 5' portion of a highly expressed endogenous gene, for example, the A. awamori glucoamylase gene;
(d) a linker sequence encoding kex2 peptidase cleavage site;
(e) DNA encoding the amino acids for human lactoferrin;
(f) a transcription termination sequence from the A. niger glucoamylase gene; and
(g) a phleomycin resistance selectable marker gene; wherein said transformed Aspergillus awamori, niger and oryzae fungal cells are cultured in a suitable nutrient medium until; lactoferrin protein is formed as a fusion product and then processed by an endogenous proteolytic enzyme specific for the Kex2 peptidase cleavage site, wherein said lactoferrin protein is the product of the cDNA encoding the amino acid sequence of human LF and, wherein lactoferrin is secreted into the nutrient medium and isolated therefrom. For the purpose of this invention, "Kex2 peptidase cleavage site" and "kex2 peptidase recognition sequence" are used interchangeably.
Another embodiment of this invention is a method of isolating lactoferrin from fungal nutrient medium comprising culturing a transformed Aspergillus fungal cell containing a recombinant plasmid vector, wherein said plasmid vector comprises a promoter, signal sequences, a 5' portion of the glucoamylase gene, linker sequences, DNA encoding the amino acids of human lactoferrin, transcription termination sequences, and a selectable marker gene and wherein said transformed Aspergillus fungal cells are cultured in a suitable nutrient medium until lactoferrin protein is formed as a fusion product and then processed by an endogenous proteolytic enzyme, and wherein lactoferrin is secreted into the nutrient medium and isolated therefrom.
The above described method of isolating lactoferrin from fungal nutrient medium is further defined wherein the plasmid vector contains a promoter from the A. awamori glucoamylase gene, a signal sequence from A. awamori glucoamylase gene, a 5' portion of the A. awamori glucoamylase gene, a linker sequence encoding kex2 peptidase cleavage site, a transcription termination sequence from the A. niger glucoamylase gene, and a phleomycin resistance selectable marker gene.
Another embodiment of this invention is a novel recombinant expression plasmid vector comprising the following components operably linked from 5' to 3':
1) promoter from the A. awamori glucoamylase gene;
2) signal sequence from the A. awamori glucoamylase gene;
3) 5' portion of the A. awamori glucoamylase gene;
4) linker sequence encoding kex2 peptidase cleavage site;
5) a nucleotide sequence encoding the amino acids for human lactoferrin or lactoferrin polypeptide fragments;
6) transcription termination sequence from the A. niger glucoamylase gene; and
7) phleomycin resistance selectable marker gene.
The invention also comprises production of the complete and partial sequences of the cDNA for human, bovine or porcine lactoferrins and substitution analogs or allelic variations thereof which code for biologically active polypeptides having homology with a portion of lactoferrin, especially those that are not available from enzyme digests of natural lactoferrins, the method of making polypeptides by use and expression of partial cDNA sequences, and the polypeptide products produced by the methods of this invention. The desired partial sequences can be produced by restriction enzyme cleavage, as for example at the cleavage sites indicated in FIGS. 13, 14, and 15. FIG. 13 through 15 shown restriction enzyme cleavage sites for the human, bovine and porcine LF cDNA sequence, respectively. The partial sequences may also be synthesized, obtained by PCR amplification, by a combination of cleavage, ligation and synthesis, or by other methods known to those skilled in the art.
The cDNA sequence for porcine lactoferrin (Lydon, J. P., et al., Biochem. Biophys. ACTA, 1132:97-99 (1992); Alexander, L. J., et al., Animal Genetics, 23:251-256 (1992)) and for bovine lactoferrin (Mead, P. E., et al., Nucleic Acids Research, 18:7167 (1990); Pierce, A., et al., Eur. J. Biochem., 196:177-184 (1991)) have since been determined and reported in the literature. The references containing the cDNA sequences for bovine and porcine lactoferrin are herein incorporated into this patent application by reference.
Fragments of polypeptides derived from lactoferrin are also known to be biologically active and they may be produced by the method of the present invention. An N-terminal human lactoferrin fragment, including a bactericidal domain of hLF, was isolated from a pepsin digest of intact hLF. Bellamy, W. M., et al., Biochem. Biophys. ACTA, 1121:130-136 (1992). Synthetic 23 and 25 amino acid polypeptides were synthesized and found to have activities similar to the fragment derived by pepsin digestion. The synthesis details, yields and purity of the synthetic peptide were not reported. Bellamy et al. do not provide a practical route to large scale production of the bovine or human lactoferrin polypeptides free of the contaminants resulting from isolation from natural products. These polypeptides fragments may be produced by the method of the present invention, and form a preferred embodiment thereof.
The amino acid sequences and corresponding cDNA sequences for the following disclosures are incorporated herein by reference:
(a) Powell et al., Nucleic Acids Research, 18(13): 4013 (1990; mammary);
(b) Rey et al., Nucleic Acids Research, 18(17): 5288 (1990; mammary);
(c) Rado et al., Blood, 70(4): 989-993 (1987; neutrohil);
(d) Stowell et al., Biochem. J., 276:349-5 (1991);
(e) Panella et al., Cancer Research, 51: 3037-3043 (1991; mammary); and
(f) Johnston, et al., Blood,. 79(11): 2998-3006 (1992; leukemic).
Any of these sequences, or modified forms of these sequences may be used in the method of the present invention, the preferred sequence is one having the polypeptide sequence reported to GenBank by the present inventors, and having Accession No. A31000, all of which are incorporated herein by reference.

BRIEF DESCRIPTION OF THE DRAWINGS
So that the manner in which the above recited features, advantages, and objects of the invention, as well as others which will become clear, are obtained and can be understood in detail, more particular descriptions of the invention briefly summarized above may be had by reference to certain embodiments thereof which are illustrated in the appended drawings. These drawings form a part of this specification.
It is to be noted, however, that the appended drawings illustrate preferred embodiments of the invention and therefore not to be considered limiting of its scope. The invention may admit to other equally effective equivalent embodiments.
FIG. 1 shows the construction of the plasmid vector containing the hLF cDNA for expression in Aspergillus awamori designated "pPLF-19." Abbreviations used in this figure are as follows: Apr: ampicillin resistance; hLF: human lactoferrin; GA: glucoamylase; pGA: promoter from glucoamylase; GA 3'UTR: glucoamylase 3' untranslated region; s.s.: signal sequence; phleo r: phleomycin gene resistance. Example 4 details the construction of this vector.
FIG. 2 is an SDS-PAGE of recombinant hLF (500 ng) purified from the growth medium of Aspergillus awamori transformants containing pPLF-19.
FIG. 3 is a Western blot of glycosylated (1 .mu.g) and deglycosylated recombinant hLF (1 .mu.g) purified from the growth medium of Aspergillus awamori transformants containing pPLF19.
FIG. 4 presents the results from N-terminal sequencing of the first 10 amino acids of recombinantly produced hLF in A. awamori.
FIG. 5 presents the results of an iron binding and saturation of standard and recombinant hLF study.
FIG. 6 presents the results from comparing the pH stability of iron-binding to standard and recombinant hLF.
FIG. 7 presents the antimicrobial action of natural and recombinant hLF against E. coli 0111.
FIG. 8 presents the results obtained from studies on antimicrobial action of natural and recombinant hLF against Shigella flexneri.
FIG. 9 presents the results of antimicrobial action of natural and recombinant hLF against Shigella flexneri in a time kill study.
FIG. 10-A and FIG. 10-C outline the design, intermediates, and construction of universal Aspergillus awamori expression shuttle vector pPLF-26. Note that not all restriction sites are shown in these figures.
FIG. 11 presents a detailed description of a universal shuttle vector pPLF-26 which contains unique NotI and EcoRI sites for cloning.
FIG. 12 presents the results from digesting pPLF-26 and pPLF-19 with various restriction enzymes to confirm the presence of the unique NotI and EcoRI sites, and the orientation of the plasmid.
FIG. 13 shows restriction enzyme cleavage sites for the human LF cDNA sequence.
FIG. 14 shows restriction enzyme cleavage sites for the bovine LF cDNA sequence.
FIG. 15 shows restriction enzyme cleavage sites for the porcine LF cDNA sequence.
FIG. 16A represents Western immunoblot analysis of recombinant hLF produced in A. oryzae.
FIG. 16B represents silver-stained SDS-polyacrylamide gel analysis of duplicate samples as in Panel 16A.
FIG. 16C represents N-terminal amino acid sequence of recombinant hLF produced in A. oryzae.

DETAILED DESCRIPTION OF THE INVENTION
Definitions
For the purpose of the subject application, the following terms are defined for a better understanding of the invention.
The term "transferrin family" means a family of iron binding proteins including serum transferrin, ovotransferrin and lactoferrin. These proteins are all structurally related.
The term "lactoferrin" means a member of the transferrin family which is found in milk and other secretions. Lactoferrin is an 78 KD iron binding protein.
Additionally, the term "domain" is used to define a functional fragment of the lactoferrin protein or lactoferrin polypeptide which includes all or part of the molecular elements which effect a specified function such as iron binding, bactericidal properties, receptor binding, immune stimulation, etc.
The term "polypeptide" or "polypeptides" means several amino acids attached together to form a small peptide or polypeptide.
The term "substitution analog" or "allelic variation" or "allelic variant" all refer to a DNA sequence which one or more codons specifying one or more amino acids of lactoferrin or a lactoferrin polypeptide are replaced by alternate codons that specify the same amino acid sequence with a different DNA sequence. Where "substitution analog" or "allelic variant" refers to a protein or polypeptide it means the substitution of a small number, generally five or less amino acids as are known to occur in allelic variation in human and other mammalian proteins wherein the biological activity of the protein is maintained. Amino acid substitutions have been reported in the sequences of several published hLF cDNAs which are most likely due to allelic variations. See FIG. 16, and discussion related to this Figure.
The term "vector(s)" means plasmid, cosmid, phage or any other vehicle to allow insertion, propagation and expression of lactoferrin cDNA.
The term "host(s)" means any cell that will allow lactoferrin expression.
The term "promoter(s)" means regulatory DNA sequences that control transcription of the lactoferrin cDNA.
The term "multiple cloning cassette" means a DNA fragment containing unique restriction enzyme cleavage sites for a variety of enzymes allowing insertion of a variety of cDNAs.
The term "transformation" means incorporation permitting expression of heterologous DNA sequences by a cell.
The term "iron binding capacity" means ability to bind Fe. Fully functional human lactoferrin can bind two atoms of iron per molecule of LF.
The term "biological activity or biologically active" means functional activity of lactoferrin as measured by its ability to bind iron, or kill microorganisms, or retard the growth of microorganisms, or to function as an iron transfer protein, or bind to specific receptors, stimulate immune response or regulate myelopoiesis.
The promoter useful in the present invention may be any that allows regulation of the transcription of the lactoferrin cDNA. Preferably, the promoter is selected from the group of alcohol dehydrogenase, .alpha.-amylase and glucoamylase genes. Thus, many different promoters are known to those skilled in this art but the inventors prefer to use the glucoamylase promoter isolated from A. awamori.
Many different signal sequence and sources of these signal sequences are known to those skilled in this art but the inventors prefer to use the glucoamylase signal sequence plus the 5' portion of the glucoamylase gene derived from A. awamori.
The signal sequence useful in the present method may be any that contains a translation initiation codon and secretory signal together with part of a coding region for any highly expressed endogenous gene.
The linker sequence useful in the present method contains a recognition sequence for any proteolytic enzyme, preferably the Kex2 peptidase recognition sequence.
The transcription termination sequence useful in the present method may be any that allows stabilization and correct termination of the lactoferrin mRNA transcripts. Preferably, the transcription termination sequence is derived from the .alpha.-amylase, glucoamylase, alcohol dehydrogenase or benA genes. Thus, many different transcription termination sequences are known to those skilled in this art but the inventors prefer using the 3' untranslated region from the glucoamylase gene from A. niger.
The selectable marker gene useful in the method of the present invention may be any that permits isolation of cells transformed with a lactoferrin cDNA plasmid. Preferably, the selectable marker gene is selected from pyr4, pyrG, argB, trpC, amdS, or phleomycin resistance genes. Thus, many different selectable markers are known to those skilled in this art but the inventors prefer to use the phleomycin resistance gene.
Additionally, recombinant production of lactoferrin protein has been described above in its preferred embodiments. LF can be produced in a number of sources: cell sources such as Aspergillus; Saccharomyces cerevisiae, Kluyveromyces lactis, or Pichia pastorsis; insect cells such as SF9; and mammalian cells such as Cos cells.
The cells, preferably eukaryotic cells, useful in the present invention are any that allow for integration of a vector, preferably a plasmid comprising the lactoferrin cDNA and expression of the lactoferrin cDNA. Preferably, the eukaryotic cells are filamentous fungal cells or insect cells. Insect cells such as SF9 are useful in the method of the present invention. More preferably, the cells are fungal Aspergillus cells. Most preferably, the eukaryotic cells useful in the present invention are Aspergillus strains, such as A. oryzae, A. niger, A. nidulans and A. awamori.
The confirmation of the cDNA sequence encoding hLF and the deduced amino acid have been proven by multiple confirmation procedures. These are:
1. Multiple sequence analyses.
2. Transcription and translation of hLF protein from the cDNA with positive identification using an anti-hLF antibody.
The cDNA sequence encoding hLF can be used to prepare recombinant human lactoferrin, thus making available a source of protein for therapeutic and nutritional applications. The confirmed cDNA sequence can be used in an appropriate cloning vehicle to replicate the cDNA sequence. Also, the cDNA can be incorporated into a vector system for human lactoferrin production. Other lactoferrin DNA sequences can be substituted for the human lactoferrin cDNA sequence to provide bovine, porcine, equine or other lactoferrins. Partial cDNA sequences can also be employed to give desired lactoferrin derived polypeptides. The expression systems of the invention can be used to provide lactoferrin derived polypeptides that are not available by enzymatic digestion of naturally occurring lactoferrin. The subject invention further provides an expression system for producing lactoferrin and lactoferrin related polypeptides in Aspergillus cells. The invention allows for the production of lactoferrin free of lactoperoxidase, lysozyme, or other proteins that are contaminants of lactoferrin isolated from milk or other natural sources. This invention is not limited to any particular uses of the human cDNA sequence or production of lactoferrin of other species from the appropriate DNA sequences.
The recombinant LF being a protein derived by recombinant techniques can be used in a variety of applications. The human gene can be transferred to mammalian systems such as cows and other agriculturally important animals and expressed in milk. The incorporation of a lactoferrin gene and expression in the milk of animals can combat an iron deficiency typical in piglets. The inclusion of a lactoferrin gene with expression should improve an animal's disease resistance to bacterial and viral infection. The tissue specific expression of human lactoferrin in mammary glands, for instance, would impart the bacteriocidal and virucidal benefit of the expressed gene to young feeding on the milk and would provide a production means for the secreted protein for therapeutic use.
The LF produced by recombinant methods of the subject invention can be used in a variety of products including human or animal foods, as therapeutic additives to enhance iron transport and delivery, and for the virucidal and bacteriocidal qualities, as additives for eyedrops, contact lens and other eye care solutions, topical skin care products, eardrops, mouthwashes, chewing gum and toothpaste. The recombinant LF would provide a safe, naturally occurring product which can be topically applied as well as ingested safely. The bactericidal lactoferrin polypeptides are useful as preservatives in the above listed products, and as therapeutic anti-infection agents. The iron binding polypeptides are useful as iron or other metal ion carrier proteins for nutritional and therapeutic uses, and as bacteriostats and bactericides, especially in products of the types listed above. Each protein may also be used as a nutrition supplement and as a source of amino acids and metals.
Different components of plasmid expression vectors as used to produce recombinant human lactoferrin are presented below and are not meant to be limitations of the present invention in any form. Many different promoters are known to those skilled in this art but the inventors prefer to use the glucoamylase promoter isolated from A. awamori. Many different signal sequence and sources of these signal sequences are known to those skilled in this art but the inventors prefer to use the glucoamylase signal sequence plus the 5' portion of the glucoamylase gene derived from A. awamori. Many different linker sequences are known to those skilled in this art but the inventors prefer to use a synthetic linker which codes for the Kex2 peptidase cleavage site. Many different transcription termination sequences are known to those skilled in this art but the inventors prefer using the 3' untranslated region from the glucoamylase gene from A. niger. Many different selectable markers are known to those skilled in this art but the inventors prefer to use the phleomycin resistance gene.
One of ordinary skill in this art understands and appreciates that a variety of different parameters can be modified while not affecting the quantity or quality of lactoferrin produced by the claimed invention. The following is a list of such parameters that can be altered and yet still not affect the amount and quality of lactoferrin produced: temperature; pH; nutrients required; scale-up considerations; type of equipment used; ratio of oxygen/air used; use of stirred vs. static systems; harvest times, etc.
Different growth and production conditions can be used for the expression of recombinant human lactoferrin in Aspergillus awamori. The following descriptions are presented for the purposes of illustrating various conditions which can be used for the expression of hLF in Aspergillus awamori and are not meant to be limitations of the present invention in any form. Presented below is a general outline of the fermentation production process and the process used to recover the produced lactoferrin. One of ordinary skill in this art understands that the protocol may be changed or modified in minor ways in order to enhance the production of the desired lactoferrin or lactoferrin polypeptide.
The following examples are given for the purposes of illustrating various embodiments of the present invention and are not meant to be limitations of the present invention in any form.
EXAMPLE 1
CONSTRUCTION OF EXPRESSION VECTOR pPLF-19 FOR THE EXPRESSION OF RECOMBINANT HUMAN LACTOFERRIN IN ASPERGILLUS AWAMORI.
This example demonstrates the construction of an expression vector which is used to express recombinant human lactoferrin in Aspergillus awamori.
I. STRAINS, PLASMIDS, ENZYMES AND MEDIA
A. Bacterial and fungal strains
Aspergillus awamori strain ATCC 22342 was used as the host strain for the heterologous expression of human lactoferrin. E. coli strain DH5.alpha. was used in the construction of the human lactoferrin expression vector, pPLF-19.
B. Plasmids
The plasmids pUC19 and pGEM4 (Promega, Madison, Wis.) were used in various cloning steps leading to the final construction of the human lactoferrin expression plasmid pFLr-19.
The phleomycin resistance vector, pLO-3, which contains the phleomycin resistance gene (a phleomycin binding protein gene from Streptoalloteichus hindustanus) coupled to a yeast cytochrome C1 terminator was derived from the plasmid pUT713 (CAYLA, Toulouse-Cedex, FR). It is expressed in fungus by the .beta.-tubulin promoter from A. niger.
C. Enzymes
Restriction enzymes were obtained from New England Biolabs (Beverly, Mass.). T4 Ligase, T4 Polymerase, T4 Kinase, and the Klenow fragment from E.coli DNA Polymerase I were purchased from Bethesda Research Laboratories (BRL, Gaithersburg, Md.). Mung Bean Nuclease was obtained from Stratagene (La Jolla, Calif.). Taq Polymerase was obtained from Promega Corporation (Madison, Wis.). DNA sequencing of plasmid constructs was accomplished using the Sequenase Version 2.0 T7 DNA Polymerase enzyme and kit (United Stated Biochemicals, Cleveland, Ohio). Novozym 234, a spheroplasting enzyme was purchased from Novo BioLabs (Bagsvaerd, Denmark).
D. General Growth Media
E. coli strains were grown in L-broth (Difco, Detroit, Mich.). Bacterial transformants were grown on L-broth plates containing 1.5% agar and 125 ug/ml ampicillin. Complete Media (CM) for growth of A. awamori in liquid is composed of: 50 ml of 20.times.Clutterbuck's salts (120 g Na.sub.2 NO.sub.3, 10.4 g KCl, 10.4 g MgSO.sub.4 7 H.sub.2 O, 30.4 g KH.sub.2 PO.sub.4), 2.0 ml Vogel's Trace Elements (0.3M citric acid, 0.2M ZnSO.sub.4, 25 mM Fe[NH4].sub.2 [SO.sub.4].sub.2 6 H.sub.2 O, 10 mM CuSO.sub.4, 3 mM SO.sub.4.sup.-2, 8 mM boric acid, 2 mM Na.sub.2 MoO.sub.4,2 H.sub.2 O), 5.0 g tryptone, 5.0 g yeast extract, 10 g glucose in one liter of distilled water). 1.5% agar was added for CM slants. PDA slants contained 39.0 g/L Potato Dextrose Agar in water (Difco, Detroit, Mich.), 10.0 g/L glucose, 10.0 g/L agar, 0.1 g/L MgSO4 7 H.sub.2 O, 0.12 g/L KH.sub.2 PO.sub.4, 0.25 g/L (NH4).sub.2 HPO.sub.4.
A. awamori lactoferrin-producing transformants were grown in KT-4 media: 150 g/L maltose, 60 g/L soyfine soymilk LF, 79.8 g/L C.sub.6 H.sub.5 O.sub.7 Na.sub.3,2 H.sub.2 O, 15 g/L, [NH4].sub.2 SO.sub.4, 1.0 g/L NaH.sub.2 PO.sub.4, 2.05 g/L MgSO.sub.4 7 H.sub.2 O, 1.0 ml/L Tween 80, 2.0 ml/L antifoam 204; Dunn-Coleman et al., 1991, Bio/technology 9: 976-981.
E. ATCC Cell Deposit
The following transformed strain was deposited with the American Type Culture Collection pursuant to the provisions of the Budapest Treaty for the International Recognition of the Deposit of Microorganisms for the Purposes of Patent Procedure (American Type Culture Collection, 12301 Parklawn Drive, Rockville, Md. 20852) by the Applicants on Jul. 8, 1994: "Awa LF 24-1" is Aspergillus awamori transformed with the expression plasmid pPLF-19 containing the cDNA encoding human lactoferrin. This deposit was given ATCC Accession Number 74290. Applicants further agree to make this deposit available, without restriction to responsible third parties upon the granting of a patent from this application in the United States and comply with existing laws and regulations pertaining thereto, without limitation, except as to third parties adherence to applicants rights as prescribed by the claims of a patent issuing from this application.
II. METHODS
A. Construction of Human Lactoferrin Expression Plasmids
The following plasmids were constructed as progenitors to the final expression plasmid, pPLF-19. A diagram of the pPLF-19 construct is shown in FIG. 1. Abbreviations used in this figure are as follows: Apr: ampicillin resistance; hLF: human lactoferrin; GA: glucoamylase; pGA: promoter from glucoamylase; GA 3'UTR: glucoamylase 3' untranslated region; s.s.: signal sequence; phleo r: phleomycin resistance vector.
pPLF-1
The hLF cDNA was removed from pGEM4hLFc as a 2.3 kb SacI/HindIII fragment and subcloned into vector pUC-19. This subcloning was made in order to remove the cDNA from the pGEM4 backbone which contains an unwanted NgoMI site.
pPLF-2
The 5' end of hLF was modified to introduce a unique NgoMI site which can be used for a seamless addition of the glucoamylase (GA) promoter and signal sequence. Modification was made through PCR amplification of a 270 bp fragment spanning the 5' end of the mature lactoferrin coding sequence to a unique AccI site. The primers are listed below and are shown in SEQ. ID. No. 1 and 2, respectively.
Kpn I NgoMI5hLFFW 5'-G GGG TAC CGC GCC GGC CGT AGG AGA AGG AGT G Gly Arg Arg Arg Arg Ser (Mature hLF N-term) AccI5hLFRV 5'-TTCGGTCCCGTAGACTTCCGCCGCT
The 270 bp fragment was amplified using Promega's Taq Polymerase with the following conditions: 1.25 to 5 mM MgCl2; 0.5 .mu.M each primer (5hLFFW and 5hLFRV); 10 ng pGEM4hLFc as template. Cycled in Perkin Elmer 9600 Thermocycler: 1 @ 2 min, 96.degree. C.; 30 @ 20 see, 96.degree. C./20 sec, 55.degree. C./20 sec 72.degree. C.; 1 @ 5 min, 72.degree. C.
Fragments were isolated from agarose, enzymatically blunted and phosphorylated and subcloned into pUC 19 cut with SmaI to give plasmid pPUC270. Sequence of the amplified product was confirmed using M13 universal forward and reverse primers. The fragment was then removed from pPUC270 as a KpnIAccI fragment and used to replace the KpnIAccI fragment of pPLF-1. The resulting plasmid was designated pPLF-2.
pPLF-6
A 280 bp EcoRI/PstI fragment carrying the last 17 bp of hLF and 160 bp of GA 3' untranslated region (UTR) was subcloned from vector pAhLFG(+1) into EcoRI/PstI cut pUC19.
pPLF-7
The modified hLF gene of pPLF-2 was subcloned as an EcoRI fragment into vector pPLF-6. Correctly oriented plasmid (pPLF-7) contains full length mature hLF sequence with a unique NgoMI site immediately upstream and 160 bp of GA 3' UTR immediately downstream. GA promoter and signal sequences (see below) will be added to this vector.
The GA promoter and signal sequence was obtained by PCR amplification from genomic DNA isolated from A. awamori strain ATCC 22342. The forward primer spans a SacI site approximately 1.1 kb upstream of the GA signal sequence. Sequence of this primer was designed from published sequence for ATCC 10864 (GenBank Accession number X56442) and are shown in SEQ. ID. No. 3 and 4, respectively.
______________________________________TATGCAGAGGAGCTCTCCCCTGAC SacI______________________________________
The reverse primer incorporates an NgoMI site for attachment to hLF.
NgoMIGARV:5'-GAT TCC GCC GGC CAA CCC TGT GCA GAC GAG GC .rarw.Ala Leu Gly Thr Cys Val Leu .rarw. .uparw. (Processing point)
Correct sized fragments (1.1 kb) were amplified from ATCC 22342 genomic DNA using the following conditions: 2.5 mM MgCl.sub.2,: 0.5 .mu.M each primers (GAFW and GARV) and 100 ng genomic DNA. Cycling parameters were set at 1 @ 2 min, 95.degree..cndot.C.; 30 @ 30 see, 95.degree. C./30 sec 60.degree. C./45 sec, 72.degree. C.; and 1 @ 5 min 72.degree. C.
Amplified products were blunted, phosphorylated and subcloned into pUC-19 cut with SmaI. DNA sequence was generated from the 3' end of the amplified fragment to check for fidelity of amplification spanning the GA signal sequence region. Clones with verified sequence were used as the stock source of GA promoter and s.s. fragments.
pPLF-9
The PCR amplified GA promoter and signal sequences was ligated to vector pPLF-7 as a SacI/NgoMI fragment to give vector pPLF-9. Sequence generated through the junctions in one direction verified a clean ligation.
PPLF-18
The final GA expression plasmid contains the GA promoter, signal sequence, and sequence encoding 498 aa of pro-glucoamylase fused to hLF. The pro-hexapeptide of glucoamylase which ends in the dibasic KEX-2 recognition sequence Lys-Arg is engineered between the GA and hLF sequences. Presumably, the chimeric protein will be better recognized by the endogenous GA secretory pathway resulting in higher secretion titers of hLF. The KEX-2 linker should allow for accurate processing of hLF away from GA.
pPLF9 was cut first with NgoMI. The ends were filled with dCTP using Klenow fragment. Mung bean nuclease was then used to remove the remaining 5' overhangs to give a blunt end ready for an in-frame protein fusion. The vector was then cut with NsiI in order to accept the GA sequence which was PCR amplified as described below.
A fragment encoding the desired GA fragment was PCR amplified from strain ATCC 22342 with the following set of primers as shown in SEQ. ID. No. 5, 6, and 7, respectively.
GA-1:5'-GAATTCAAGCTAGATGCT
This forward primer spans bases 1-18 of published ATCC 22342 (NRRL 3112) GA upstream sequence (Nunberg et al. Mol Cell Bio 1984, p 2306-2315). This sequence lies approximately 50 bp upstream of a unique NstI site which was used in the construction.
Ser Val Thr Ser Thr Ser Lys Asn Val Ile Ser Lys Arg 5'- AGC GTG ACC TCG ACC AGC AAG AAT GTG ATT TCC AAG CGCKX2GA: 3'- TCG CAC TGG AGC TGG TCG TTC TTA CAC TAA AGG TTC GCG-5'
This reverse primer sequence is complementary to the inserted pro-hexapeptide (underlined) encoding sequence and followed by the complement of pro-GA sequence encoding as 492-498.
The 2.0 kb fragment was PCR amplified using Taq polymerase. 2.5 mM MgCl.sub.2 was empirically determined to give the best amplification. The fragment was enzymatically blunted with Klenow in order to clean up potentially ragged ends leftover from the amplification. The blunted fragment was then cut with NsiI and then subcloned into manipulated vector pPLF-9 (see above) as an NsiI/blunt fragment to give plasmid pPLF-18. Sequence was verified through the GA/KEX-2/hLF junction through di-deoxy sequencing.
pPLF-19
A phleomycin resistance marker derived from CAYLA vector pUT713 (Streptoalloteichus hindustanus ble gene) and expressed from the A. niger tubulin promoter (pPLO-3) was added to pPLF-18 as a 2.3 kb HindIII fragment to give the final expression plasmid pPLF-19.
B. DNA Transformation of Aspergillus awamori Strain ATCC 22342.
Aspergillus awamori strain ATCC 22342 was spheroplasted and transformed by a procedural modification of Tilbum et al, 1983, Gene 26: 205-221. Conidating cultures of A. awamori ATCC 22342 grown on Complete Media (CM) slants for four to seven days at 30.degree. C. were scraped with 2 mls of NP40 water (0.005% Nonidet-40) to obtain a spore suspension. One ml of the spore suspension (approximately 1.times.10.sup.8 spores) was added to 50 mls of CM and grown for 22 hours at 30.degree. C., 200 rpm. Mycelia was collected by filtration through a double layer of cheesecloth and added to 50 mls of KCM buffer (Cantoral, et al., 1987, Biotechnology 5 494-497; KCM: 0.7 M KCl, 10 mM MOPS, pH 5.8) with 5 mg/ml of Novozym 234 (Novo Biolabs, Bagsvaerd, Denmark) and incubated at 30.degree. C., 90 rpm overnight for spheroplast generation.
The spheroplasts were harvested by filtration through a funnel packed with miracloth (Calbiochem; La Jolla, Ga.) and covered with cheesecloth into four 15 ml conical centrifuge tubes, then spun at 1800 rpm for ten minutes in a bench-top centrifuge. The pellets were gently resuspended in a total of 15 mls-of KCM buffer and re-centrifuged. The pellet was again washed in 15 mls of KCM buffer, then resuspended in KCMC (KCM+50 mM CaCl.sub.2) buffer to a final density of 5.times.10.sup.7 cells/ml.
Five ugs of pPLfF19 plasmid DNA in 20 .mu.l TE buffer (10 mM Tris-HCl, 1 mM EDTA, pH 8.0) was added to 200 ul of spheroplasts, and 50 .mu.l of PCM (Cantoral et al; PCM: 40% PEG 8000, 10 mM MOPS, pH 5.8, 50 mM CaCl.sub.2 [CaCl.sub.2 added prior to use]) was gently pipetted into the DNA-spheroplast mixture and incubated on ice for thirty minutes.
One ml of freshly prepared PCM was added to the transformation mix, the mix was pipetted into 50 mls of Regeneration Agar (CM+1.3M Mannitol, 3% agar) cooled to 50.degree. C. that was then divided into five petri plates. Spheroplasts were allowed to regenerate 3 to 5 hours at 30.degree. C. before overlaying with an equal amount of OL+120 ug/ml phleomycin (OL: 1% peptone, 1% agar; phleomycin [CAYLA; Toulouse, FR]). Putative transformants were transferred to PDA slants containing 125-150 ug/ml phleomycin.
C. Fermentation Conditions for Human Lactoferrin Expression in Aspergillus awamori
Spores from putative HLF-producing transformants were transferred from selective PDA slants to CM slants and grown for four days at 30.degree. C. Conidia was harvested by scraping the slant with 1.5 ml of NP40 Water, and aliquot of 1.times.10.sup.8 spores was added to 30 ml of KT-4 media in a 25 C ml flask. Cultures were fermented for six days at 30.degree. C. 200 rpm. Lactoferrin samples were collected by centrifuging one ml of fermentation 25 broth at 3000 rpm for 15 minutes and assaying the retained supernatant.
D. Human Lactoferrin Assay
Lactoferrin was quantified by a modification of a Non-Competitive Avidin-Biotin Immuncassay developed by Vilja et al, 1985, J. of Imm. Methods 76: 73-83. A ninety-six well microtiter plate (U-Bottom Microtest III; Baxter, Chicago, Ill.) was coated with 100 ul of 0.1 ug/ml rabbit antihuman lactoferrin antibody (Sigma, St. Louis, Mo.) in Coating Buffer (0.1M Sodium Carbonate/Bicarbonate, pH 9.6), and was shaken overnight at 4.degree. C.
The next day, the coating solution was removed, and the plates were washed three times with Washing Buffer (1.times.PBS pH 7.4, 0.5% Tween 20) prior to blocking with 250 ul of Diluent Buffer (1.times.PBS pH 7.4, 1% BSA [Fraction V, RIA grade, United States Biochemicals, Cleveland, Ohio], 0.05 Tween 20) for at least one hour at room temperature. The Diluent Buffer was discarded and 100 ul of diluted fermentation samples and known lactoferrin standards were added to the plate, which was then incubated for one hour at 37.degree. C. The collected supernatant from the fermentation samples was diluted 1:1000 with Diluent Buffer prior to its addition to the microtiter plate. Lactoferrin standards consisted of human lactoferrin (Sigma, St. Louis, Mo.) diluted 1 to 1000 ng/ml in Diluent Buffer.
After reaction at 37.degree. C. the samples were discarded and the plate was washed three times with Wash Buffer. One hundred ul of biotinylated anti-HLF antibody (Biotin-SP-Rabbit anti-hLF IgG, Jackson Immuno-Research Labs) diluted 1:7500 in Diluent Buffer from a 1 mg/ml stock was added to each well and incubated for one hour at 37.degree. C.
The solution was discarded, and the plate was washed three times with Wash Buffer before adding 100 ul of ABC reagent (Vectastain ABC Kit, Vector Labs, Burlingame, Ga.) and incubating the plate at 37.degree. C. for one hour. Vectastain Reagent A was diluted 1:200 and Reagent B was diluted 1:400 in Diluent Buffer prior to combining both solutions and allowing them to preincubate one hour at room temperature before use.
The ABC solution was discarded and the plate was washed five times with Wash Buffer. One hundred ul of OPD Substrate Solution (10 ml Substrate Buffer [25 mM citric acid, 50 mM Na.sub.2 HPO.sub.4 7 H.sub.2 O, pH 5.0], 8 mg o-Phenylenediamine [Bethesda Research Labs, Gaithersburg, Md.], 100 ul 30% H.sub.2 O.sub.2 [Sigma, St.Louis, Mo.]) was added and the plate was incubated in the dark for twenty minutes with gentle agitation at room temperature. After color development, 100 ul of 2M H.sub.2 SO.sub.4 was added to stop the reaction. The plate was then read at 490 nm, and lactoferrin concentrations were determined by comparison to the known standards.
EXAMPLE 2
EXPRESSION AND PROCESSING OF hLF (pPLF-19) IN ASPERGILLUS AWAMORI
When the human lactoferrin expression cassette pPLF-19 is transformed into A. awamori 22342, secreted lactoferrin is detected in the media by both the ELISA assay and by Western blot analysis. One transformant, #19-254, produces approximately 250 mg/l of human lactoferrin (hLF). A more preferred transformant, Awa LF 24-1 (ATCC Accession No. 74290; #19-24.1) produces approximately 500 mg/l of human lactoferrin. Experiments improving yield and strain development are ongoing in order to increase the production of recombinant hLF in A. awamori. To date, the inventors have obtained titers >900 mg/l hLF produced in A awamori transformants containing strain Awa LF 24-1. The results are shown in the comparative Production Table below.
Since the pPLF-19 expression product is a chimeric protein made up of 498 amino acids of glucoamylase and the complete coding region of hLF separated by a KEX-2 cleavage site, SDS-PAGE, and silver staining, Western blot analysis and N-terminal sequencing were conducted to determine whether the protein was correctly processed.
A. Silver stained SDS-Polyacrylamide Gel Analysis of Recombinant Human Lactoferrin Purified from Aspergillus awamori Transformants.
Recombinant human lactoferrin was purified from the growth medium of Aspergillus awamori transformants by ion-exchange chromatography using CM-Sephadex C50 (Stowell, K. M. et al., Biochem J., 276: 349-355). Standard human breast milk LF (Std hLF) and purified recombinant hLF (Rec hLF) were resolved on a 7.5% SDS-Polyacrylamide gel and silver-stained. The results of this analysis are shown in FIG. 2. The recombinant hLF protein migrates at the expected size for processed hLF (lane 2) and is identical as in size to the standard hLF (lane 1). The position of the molecular weight markers are indicated on the left.
B. Western Blot Analysis of Glycosylated and Deglycosylated Recombinant Human Lactoferrin Purified from Aspergillus awamori Transformants.
Recombinant human lactoferrin purified from the growth medium of Aspergillus awamori transformants, untreated and treated with N-glycosidase F, were resolved by SDS-polyacrylamide electrophoresis, transferred to nitrocellulose and probed using a specific IgG directed against human lactoferrin (Sigma). The results of this analysis are shown in FIG. 3. Comparison of untreated recombinant hLF with untreated standard breast milk hLF illustrate that both of these proteins co-migrate (FIG. 3 lanes 3 and 1, respectively). N-glycosidase F is an enzyme which hydrolyses the glycosylamine linkage generating a carbohydrate free peptide of smaller molecular weight. Comparison of recombinant hLF with standard hLF after treatment with N-glycosidase F illustrates that both proteins migrate identically suggesting that both proteins are similarly N-linked to carbohydrate (FIG. 3, lanes 4 and 2, respectively).
EXAMPLE 3
N-TERMINAL SEQUENCE ANALYSIS CONFIRMS THAT RECOMBINANT HUMAN LACTOFERRIN IS CORRECTLY PROCESSED IN ASPERGILLUS AWAMORI
In order to confirm that the recombinant hLF produced in A. awamori is correctly processed, the N-terminal portion of the recombinantly produced hLF was sequenced. First, recombinant hLF was expressed in A. awamori as a fusion protein to the catalytic domain of the A. niger glucoamylase gene (498 AA) which is separated by a synthetic linker which codes for KEX-2 proteolytic cleavage site. Next, the recombinant hLF was purified from the growth medium using CM-sephadex C50 (previously described by Stowell et al., Biochem J, 276: 34959 (1991)). To determine if recombinant hLF was correctly processed at its N-terminus, the first N-terminal amino acids of the purified protein were sequenced using the automated Edman degradation procedure (5 ug). The results of this analysis are outlined in FIG. 4. The sequence of the recombinant protein is identical to the corresponding amino acids in human breast milk lactoferrin. Hence, recombinant hLF has been correctly processed at the KEX-2 proteolytic cleavage site in A. awamori.
EXAMPLE 4
FUNCTIONAL ANALYSIS OF HUMAN LACTOFERRIN PRODUCED IN ASPERGILLUS AWAMORI
A. Iron Binding and Saturation of Standard and Recombinant hLF
Lactoferrin is an iron-building glycoprotein having the capacity to bind two moles of iron per mole of LF. To determine if the binding of iron by recombinant lactoferrin was saturable, an iron-binding assay was performed. To generate apo-lactoferrin, purified Rec hLF and human breast milk were dialyzed against 0.1 M citric acid, pH 2.0 followed by extensive dialysis against H.sub.2 O. The pH of the solution was slowly raised to pH 7.6 using 5 mM sodium phosphate. Increasing concentrations (0.5 to 4.0 molar excess) of FeCl.sub.3 :.sup.59 FeCl.sub.3 :NTA (400:1:8) were added to hLF (500 ug) in 1 ml binding buffer (0.025 M Tris, pH 7.8; 0.01 M Sodium bicarbonate; 0.1 M NaCl). Samples were incubated at room temperature for 30 minutes. Iron-bound hLF was separated unbound iron and NTA by passage over a NAP-10 column which been equilibrated with 15 ml of binding buffer. The amount iron bound to LF was quantified using liquid scintillation counting. The results of this analysis are outlined in FIG. 5. Recombinant and standard hLF bind iron in a similar manner. This binding of iron is dose dependent. Furthermore, binding of iron by both standard and recombinant hLF is saturable at a 2:1 molar ratio of iron to lactoferrin. Typically, saturation levels are reached at 92.5% of maximal binding. This is indicative of initial 7.5% iron still bound to the lactoferrin after dialysis. For the purpose of this invention, "standard hLF" or "natural hLF" is human lactoferrin isolated from human breast milk and purchased from Sigma.
B. pH Stability of Iron-Binding to Standard and Recombinant hLF
To determine the pH stability of iron-binding to standard and recombinant hLF, .sup.59 Fe-saturated standard and recombinant hLF (500 ug) were dialyzed against buffers ranging from pH 7.0 to pH 2.0 for 48 hours at 4.degree. C. to remove unbound iron (Stowell et al; Biochem J, 276: 349-59 (1991). Iron bound to the hLF samples after dialysis was quantified using liquid scintillation counting. The results of this analysis are shown in FIG. 6. The pH-dependent release of iron from both standard and recombinant hLF is identical. Both standard and recombinant hLF retain most of the iron over a pH range of 7-4 and are essentially iron-free at pH 2.0.
C. Antimicrobial Action of Natural and Recombinant hLF against E. coli 0111
The antimicrobial activity of both natural (standard) and recombinant hLF against E. coli 0111 was determined using an in vitro microtitre plate assay (Nonnecker and Smith., J. Dairy Sci, 67: 606-613 (1984). Briefly, a standard inoculum of logarithmic-phase cells (1.times.10.sup.6 CFU/ml) were incubated in the presence or absence of increasing concentrations of ApoStd or Apo-Rec hLF in 1% Basal Bactopeptone medium (100 ul). The samples were cultured at 37.degree. C./200 RPM for 4 hours. Aliquots were removed, serially diluted and plated overnight on MacConkey agar plates for enumeration. The results of this analysis are shown in FIG. 7. Natural and recombinant hLF exert similar dose dependent antimicrobial action against E. coli 0111 at all concentrations tested.
D. Antimicrobial Action of Natural and Recombinant hLF Against Shigella flexneri.
The antimicrobial action of both natural (standard) and recombinant hLF against S. flexneri was determined as described in Example 4(C). The results of this analysis are shown in FIG. 8. Both natural and recombinant hLF exert similar dose dependent inhibition of S. flexneri at all concentrations tested.
E. Antimicrobial Action of Natural and Recombinant hLF Against Shigella flexneri (Time Kill Study).
A time course of the antimicrobial activity of natural and recombinant hLF was carried out. Briefly, a standard inoculum of logarithmic-phase S. flexneri cells (1.times.10.sup.6 CFU/ml) were incubated in the presence or absence of ApoStd or Apo-Rec hLF (300 ug) in 1% Basal Bactopeptone medium (100 ul). The samples were cultured at 37.degree. C./200 RPM. Aliquots were removed at various time intervals (0, 1, 4 and 20 hours), serially diluted and plated overnight on MacConkey agar plates for enumeration. The results of this analysis are shown in FIG. 9. Recombinant natural and recombinant hLF exert similar antimicrobial action against S. flexneri in a time dependent manner with no detectable S. flexneri CFUs remaining after 4 hours.
EXAMPLE 5
CONSTRUCTION OF A UNIVERSAL SHUTTLE VECTOR
pPLF-26 TO ALLOW IN FRAME SUBCLONING OF ANY cDNA
This Example describes the design and construction of human lactoferrin shuttle vectors capable of expressing mutant forms of hLF in Aspergillus species. Unique NotI and EcoRI sites were created in order to facilitate the cloning of altered forms of lactoferrin into the vector. Protein is expressed under the direction of the glucoamylase promoter and signal sequence as a glucoamylase: hLF chimera, which is process in vivo through the recognition of a KEX-2 cleavage site. Both vectors also contain the glucoamylase 3' untranslated region for enhanced mRNA stability and phleomycin resistance gene for selection in Aspergillus.
I. Human Lactoferrin Expression Vector Constructions
A. Construction of pPLF-26
In order to create an expression vector capable of accepting mutuant forms of lactoferrin, several restriction sites were altered to allow for unique cloning sites. To substitute mutant forms of lactoferrin into the plasmid, the addition of a NOTI site at the 5' end of the hLF gene was designed. An EcoRI site was selected as a unique cloning site at the 3' end of the hLF gene; and, other existing EcoRI sites needed to be eliminated in order to make this site unique.
In addition to the unique cloning sites, pPLF-26 contains the Aspergillus awamori glucoamylase (GA) promoter, signal sequence, and 498 amino acids of the glucoamylase protein which is separated from hLF by a KEX-2 recognition site. The vector also contains the Aspergillus niger GA 3' untranslated region (UTR), and the phleomycin resistance gene from Streptoallotetchus hindustanus (CAYLA vector pUT713) expressed by the A. niger beta-tubulin promoter. For selection and replication in E. coli, the plasmid contains the ColEI origin of replication and the ampicillin resistance gene. The construction of hLF expression vector pPLF-26 is outlined in FIG. 10-A and FIG. 10-B, and a description of construction intermediates is listed below.
pPLF18Sp.Alt
Plasmid pPLF-18, which contains the promoter, signal sequence and partial protein sequence of glucoamylase separated from hLF by a KEX-2 recognition site, was selected as the starting plasmid for the desired site modifications. pPLF-18 was digested with SphI to isolate two fragments; the 3.3 kb fragment containing hLF was subcloned into the in vitro mutagenesis vector pALTER in the correct orientation to give pPLF18Sp.Alt.
pR18.2
The 4.4 kb Sph fragment from pPLF-18 was relegated to give pR18.2.
pNot.9
NotI restriction site spanning the KEX-2 cleavage site and hLF start site was created by in vitro mutagenesis of the vector pPLF18Sp.Alt. The NotI site, which is the result of a changing a "T" nucleotide to a "C" nucleotide, is inframe, and does not change any amino acids. The following 21 mer oligonucleotide (as shown in SEQ. ID. No. 8) was used for the mutagenesis, where the small case letter denotes a base change:
Oligo HLF NotI: NotI 5' AG CGC GGC Cgc AGG AGG A 3' . . . . . . Lys Arg GLY ARG Arg Arg Arg . . . . . . mature HLF
The mutagenic oligo HLF NotI was used in conjunction with the ampicillin repair oligo (Promega) to anneal to single-stranded pPLF18Sp.Alt DNA, which was then filled in using T4 DNA Polymerase and T4 DNA ligase. After transformation of the repair minus strain BMH 71-18 mutS and JM109, 50% of the selected transformants contained in the new NotI site, one of which was designated pNot.9.
p.DELTA.E12
Plasmid pR18.2 was digested with EcoRI and the two fragments were isolated by gel electrophoresis. Both fragments were filled in separately with Klenow, and the larger 3.6 kb fragment was dephosphorylated with calf intestinal phosphatase (CIP) at 50.degree. C. for one hour. After phenol extractions and ethanol precipitation, both filled in fragments were blunt ligated to each other. Prior to transformation, the ligation mix was digested with EcoRI to linearize any vector still containing an EcoRI site. Three clones of sixteen had both EcoRI to linearize any vector still containing an EcoRI site. Three clones of sixteen had both EcoRI sits filled in, and were in the correct orientation. One of these was designated p.DELTA.E12.
pPLF-25
p.DELTA.E12 was digested with SphI and dephosphorylated with CIP. A 3.3 kb SphI fragment containing the new NotI site was isolated from pNot.9 and ligated to p.DELTA.E12/Sph. A clone with the correctly oriented SphI fragment was designated pPLF25, which contained both unique EcoRI and NotI sites, and hLF fused to glucoamylase sequence expressed by the GA promoter.
pL03.DELTA.RI
In order to make pPLF-25 useful for selection in Aspergillus, a phleomycin resistance cassette was added. The cassette in the plasmid pLO3 contained two EcoRI sites which needed to be eliminated before the cassette could be added. Plasmid pLO3 was digested with EcoRI, both 4.3 and 0.9 kb fragments were isolated, and separately filled in with Klenow. After the fill-in reaction, the 4.3 kb fragment was treated with CIP, then purified and precipitated. Both filled-in fragments were ligated to each other overnight. Selected colonies after bacterial transformation revealed that five of twenty-four had both EcoRI sites filled in and were in the correct orientation, giving pLO3.DELTA.RI.
pPLF-26
A 2.3 kb HindIII fragment from pLO3.DELTA.RI, containing the phleomycin resistance gene transcribed by the B-tubulin promoter, was ligated to pPLF-25 digested with HindIII and dephosphorylated with CIP. Nine out of sixteen clones had the HindIII fragment in both orientations. The plasmid designated "pPLF-26" has the phleomycin resistance gene being transcribed in the same direction as the hLF gene.
FIG. 11 presents a detailed description of a universal shuttle vector pPLF-26 which contains unique Not1 and EcoRI sites for cloning. A pre-existing EcoRI site in the glucoamylase (GA) promoter region was removed by fill-in. The vector also contains the GA untranslated region, a Kex-2 cleavage site, and phleomycin resistance for selection in A. awamori. Note that all known restriction sites are shown in this figure.
FIG. 12 presents the results from digesting pPLF-26 and pPLF-19 with various restriction enzymes to confirm the presence of the unique NotI and EcoRI sites, and the orientation of the plasmid. One .mu.g of either pPLF-26 or pPLF19 DNA was digested in a 20 ul volume for one hour at 37.degree. C., with the indicated restriction enzymes. Lane 1. One .mu.g Lambda HindIII standard. Lane 2. pPLF-26 digested with EcoRI. Lane 3. pPLF-19/EcoRI. Lane 4. pPLF-26/EcoRI and NotI. Lane 5. pPLF-19/EcoRI and NotI. Lane 6. pPLF26/BamHI. Lane 7. pPLF-19/BamHI. Lane 8. pPLF-26/HindIII. Lane 9. pPLF-19/HindIII. Lane 10. pPLF-26/SphI. Lane 11. pPLF-19/SphI. Lane 12. pPLF-26/Xba (note: incomplete digest). Lane 13. pPLF-19/Xba.
This universal vector can readily be adapted to express a variety of different desired proteins. For example, the sequences of published hLF's can be inserted into this vector and expressed and isolated therefrom.
EXAMPLE 6
EXPRESSION OF BOVINE AND PORCINE LACTOFERRIN IN ASPERGILLUS AWAMORI
The universal A. awamori expression vector constructed in Example 5 can be used to allow in frame subdloning of any cDNA of interest. This vector, pPLF-26, is similar to pPLF-19 utilized for the expression of human lactoferrin in A. awamori. 5' and 3' oligonucleotide primers can be designed to contain Not1 and EcoR1 ends respectively and used to obtain the full length cDNA sequence encoding for mature porcine and bovine lactoferrin using polymerase chain reaction (PCR) amplification of their known DNA sequence. The PCR fragments can be digested with Not1, repaired using Mung Bean Nuclease (Stratagene) and all digested with EcoR1 which will allow inframe subcloning to the Not1, repaired, EcoR1 digested pPLF26. The plasmids can then be transformed into A. awamori to obtain expression and secretion from these cDNAs as previously described for human lactoferrin.
EXAMPLE 7
EXPRESSION OF HUMAN LACTOFERRIN IN DIFFERENT ASPERGILLUS STRAINS: A COMPARATIVE STUDY
This example compares the different levels of hLF expression indifferent strains of Aspergillus, specifically in A. oryzae and A. nidulans, obtained with different vector constructs. These data are to be compared with the data presented above for the expression of hLF in A. awamori.
A. Expression of Human Lactoferrin in Aspergillus oryzae
Expression plasmid, pAhLFG, was designed to contain the complete cDNA sequence encoding human lactoferrin and to be used for expression of the same in A. oryzae. The details of the design, construction, and schematic representation of pAhLFG was presented in co-pending patent application, U.S. Ser. No. 08/250,308, filed May 27, 1994, which is a continuation-in-part of application Ser. No. 07/873,304 filed Apr. 24, 1992, now abandoned. The disclosure of co-pending patent application U.S. Ser. No. 08/250,308 is herein incorporated by reference.
Expression plasmid pAhLFG contains 681 bp of 5'-flanking sequence of the A. oryzae AMY II gene that encodes the .alpha.-amylase promoter, secretary signal sequence and first codon of mature .alpha.-amylase. The cDNA coding for mature human lactoferrin is subcloned in frame downstream from these sequences allowing recombinant protein production by the addition of starch to the growth medium, the Aspergillus niger glucoamylase 3' untranslated region provides the transcription terminator and polyadenylation signals, the plasmid also contains the Neurospora crassa pyr4 selectable marker and an ampicillin resistance gene.
Southern blot analyses were performed on transformed Aspergillus oryzae strains and the data was previously presented in co-pending patent application, U.S. Ser. No. 08/250,308, filed May 27, 1994, which is a continuation-in-part of application Ser. No. 7/873,304 filed Apr. 24, 1992, now abandoned. Briefly, genomic DNA from individual transformants and control A07 were hybridized with a radiolabelled hLF cDNA probe (2.1 kb). The results demonstrated a radiolabelled fragment (2.8 kb) generated upon EcoRI digestion of the expression plasmid which is present in all the transformants (#1-9) but is absent in control untransformed A07.
Northern analyses were performed to determined if lactoferrin mRNA was transcribed correctly and efficiently in A. oryzae under the regulatory control elements of the expression plasmid. This data was previously presented in co-pending patent application, U.S. Ser. No. 08/250,308, filed May 27, 1994, which is a continuation-in-part of application Ser. No. 07/873,304 filed Apr. 24, 1992, now abandoned. Briefly, the results demonstrated that human lactoferrin mRNA was detected using .sup.32 P labelled human LF cDNA (2.0 kb) probe. Hybridization with human LF radiolabelled cDNA probe detected a specific radiolabelled band at the correct size for lactoferrin mRNA (2.3 Kb) in the transformant but not in the control untransformed strain. Quantitation of mRNA levels by dot assay showed comparable levels of expression of endogenous .alpha.-amylase mRNA between the control A07 and the transformant tested (#1).
In order to examine the levels of recombinant LF expressed and secreted from A. oryzae, a transformant (#1) was grown in the presence of 3% starch at 30.degree. C. for 72 hours. The growth medium was harvested and the mycelia washed at pH 10 to release any protein loosely associated with the cell wall (Huge-Jensen, et al., Lipids, 24:781-785 (1989)). The results are shown in FIG. 16. Western immunonoblot analysis using a specific IgG directed against human lactoferrin detected a 78 kD protein corresponding to the size of lactoferrin in the transformant which was absent in control A07. (FIG. 16A, lanes 2 and 3).
FIG. 16A: Lane 1 contains breast milk hLF standard (500 ng); Lanes 2 and 3 contain samples of the growth medium (40 ug protein) from induced control A07 and transformant #1 respectively; Lanes 4-6 contain 25 ul aliquots of eluted fractions (#35, 40, and 45 respectively) collected from the CM-sephadex purification of recombinant hLF from the growth medium.
Analysis of a duplicate silver stained SDS-PAGE gel also showed the presence of a 78 kD protein in the transformant which was absent in A07 control (FIG. 16B, lanes 2 and 3). ELISA analysis using a specific biotinylated IgG directed against hLF (Vilja, et al. J. Immunol. Methods 76:73-83 (1985)) indicates that the recombinant hLF is secreted at levels of 5-25 mg/l and represents approximately 5% of the total growth medium protein from induced cultures. There was no correlation between copy number integrated and level of recombinant protein secretion. See Table below for vector design and production levels.
Recombinant lactoferrin was purified from the growth medium of transformant #1 by ion-exchange chromatography using CM-Sephadex C5026 (Stowell, et al. Biochem. J. 276:349-355 (1991)). Human lactoferrin was eluted from the column using a linear salt gradient. An immunoreactive band corresponding to the size of hLF was detected in fractions 35-45 by Western immunoblotting using a specific IgG directed against hLF (FIG. 16A, lanes 4-6). Analysis of duplicate samples by silver stain SDS-PAGE showed that this immunoreactive hLF corresponds to the major protein band in these fractions (FIG. 16B, lanes 4-6). These results indicate that this single ion exchange chromatography step led to approximately a 95% purification of the recombinant hLF. FIG. 16B: Silverstained SDS-polyacryamide gel analysis of duplicate samples as described in FIG. 16A.
To determine if hLF was correctly processed at its N-terminus, the recombinant protein was sequenced from the N-terminus through 10 residues using the automated Edman degradation procedure. The bulk of this material was identical to the corresponding amino acids in native human milk LF (Metz-Boutigue, et al. Eur J. Biochem. 145:659-676 (1984)) with the exception of the additional alanine residue at the N-terminus (FIG. 16C) which was introduced into our plasmid construction to exactly mimic the linkage of the signal peptide to mature .varies.-amylase. A small proportion had lost the N-terminal Ala-Gly-Arg tripeptide or the Ala-Gly-Arg-Arg tetrapeptide. Previous analysis of native hLF suggests that this processing pattern may be intrinsic to the hLF protein itself (Hutchens, et al. Proc. Natl. Acad. Sci. U.S.A. 88:2994-2998 (1991)) or may be due to heterogeneity in the N-terminal processing capabilities of the A. oryzae signal peptidases (Christensen, et al. Bio/Technology 6:1419-1422 (1988); Huge-Jensen et al. Lipids 24:781-783 (1989)).
B. Expression of Human Lactoferrin in Aspergillus nidulans
A plasmid was designed and constructed for the expression of hLF cDNA in A. nidulans. The details on this vector design and construction (including all intermediate vectors) were was previously described in co-pending patent application having U.S. Ser. No. 08/145,681, filed Oct. 28, 1993.
Briefly, the A. nidulans expression plasmid, pAL3hLFT, contains 300 bp of 5'-flanking sequence of the A. nidulans alcA gene containing all the regulatory elements necessary for controlled gene expression. This vector contains the alcohol dehydrogenase promoter from A. nidulans, the natural hLF signal sequence, cDNA endocing hLF, Ben A 3' untranslated sequences from A. nidulans and the Neurospora crassa pyr4 selectable marker.
Southern blot analyses were performed on transformed Aspergillus nidulans strains and the data was previously described in co-pending patent application having U.S. Ser. No. 08/145,681, filed Oct. 28, 1993, incorporated herein by reference. Briefly, Southern blot analyses were performed to confirm that transformants contained integrated plasmid with hLF cDNA. A hLF-specific radiolabelled band was detected at the expected size (2.3 kb) in lanes 1-10 but not in DNA from control spores. These results demonstrated that hLF cDNA was integrated into the genome of all A. nidulans transformants tested and varied randomly from one copy to 20 copies per cell. The site of integration of the plasmid into the A. nidulans genome is random due to the absence of homologous sequences to target the vector into a particular site.
The specific details for the production of hLF in A. nidulans was previously described in co-pending patent application having U.S. Ser. No. 08/145,681, filed Oct. 28, 1993. Briefly, conidia (1.times.10.sup.6 /ml) were cultured in minimal media with Na acetate as carbon source with or without addition of 1.2% ethanol to induce transcription of the hLF cDNA. Media and mycelia were harvested and separated using Miracloth (Calbiochem, San Diego, Calif.). Mycelia (200 mg) were freeze-dried and lyophilized overnight. Total cellular extracts were prepared by homogenization in a glass teflon homogenizer using phosphate-buffered saline in the presence of phenylmethylsulfonylfluoride. The homogenate was centrifuged and the supernatant containing the soluble fraction was recovered. The growth medium was concentrated by freeze drying and lyophilization and resuspended in PBS. Protein concentration was determined using the Bradford reagent according to manufacturer's instructions (BioRad, Richmond, Calif.). Concentration media samples containing 40 .mu.g protein and soluble extracts (50 .mu.g protein) were subjected to SDS-PAGE. Purified lactoferrin was used as standard (hLF std). The resolved proteins were transferred to nitrocelulose filters elecrophoretically using the Western blot procedure. The filters were blocked with Tris-buffered saline containing 2% dried milk and then incubated in the same buffer with the addition of a 1 .mu.g/ml of a specific polyclonal IgG directed against hLF (Sigma, St. Louis, Mo.). The filters were washed in TBS/0.05% Nonidet P-40 followed y incubation with [.sup.125 I] protein A. The filter was then washed, dried and exposed overnight to Kodak XAR5 film at -70.degree. C. The film was then developed by autoradiography. The autoradiographs demonstrate production of hLF.
Western analyses was performed to determine if the hLF cDNA was expressed in the A. nidulans transformants under the control of the alcA promoter. Conidia (1.times.10.sup.6 /ml) from one transformant (No. 5), which contained the highest number of copies of integrated hLF cDNAs. The cultures were harvested, washed and reinoculated into minimal medium supplemented with ethanol and growth for an additional 12 or 24 h before harvesting the cultures. Cell extracts and samples of the growth medium were resolved by SDS-PAGE, transferred to introcellulose and immunoblotted using a specific polyclonal IgG directed against hLF. An immunoreactive band indistingishable from native hLF was evident in the cells and growth medium from transformant No. 5 after 12 and 24 h growth only after ethanol induction. These results demonstrate that hLF is expressed in transformed A. nidulans under the control of the alcA promoter.
Western analysis revealed hLF in the cells in all of the remaining transformants (data not shown). In general, there was a correlation between the plasmid copy number and the expression levels obtained. In the medium, hLF was detected only with transformants containing multiple copies of integrated expressed plasmids (Nos. 1, 5, 7 and 10).
The pilot fermentation of transformant No. 5 was carried to determine the approximate amount of hLF produced ELISA analysis, using a specific biotinylated IgG directed against hLF, demonstrated that the total level of recombinant hLF produced was 5 mg/l with approx. 30% (1.5-2.0 .mu.g/ml) of this material secreted into the medium. See Table below for vector design and productions levels.
Thus, this Example demonstrates that the Applicants have improved and enhanced the expression of human lactoferrin by modifying the design of the expression vector plasmid constructs and by changing the host cells used. As noted in the table below, several different vector constructs have been used to produce human lactoferrin in at least four different Aspergillus strains. The amount of human lactoferrin produced is shown in milligrams hLF per liter.
For convenience, each vector component is listed in the order that it appears in the vector construct directionally positioned from left to right. The components included in the expression plasmid vector include: a promoter and the source of the promoter, a signal sequence and the source of the signal sequence, a linker sequence, DNA encoding for human lactoferrin, a transcription termination sequence, and a selectable marker.
TABLE 1__________________________________________________________________________Human Lactoferrin Production Levels in Different Aspergillus StrainsUsing Different Vectors Signal Transcription mg/liter Promoter Sequence Linker Termination Selectable HuLFVector Host Cells (Source) (Source) Sequence cDNA Sequence Marker Produced__________________________________________________________________________A (92) A. oryzae .alpha.-amylase .alpha.-amylase -- hLF 3' untranslated pyr4 5-25 (A. oryzae) (A. oryzae) from gluco- (Neurospora amylase crassa) (A. niger)B (1093) A. nidulans Alcohol natural huLF -- hLF 3' untranslated pyr4 5 dehydrogenase signal sequence from Ben A (Neurospora (alc-A) (A. (A. nidulans) crassa) nidulans)C (0594) A. awamori Glucoamylase glucoamylase Synthetic hLF 3' untranslated phleomycin 500 (A. awamori) (A. awamori) Linker which from gluco- plus 5' 1/2 end codes for Kex2 amylase of gluco- peptidase (A. niger) amylase gene cleavage site (A. awamori)D (0894) A. awamori Glucoamylase Glucoamylase Synthetic hLF 3' untranslated phleomycin 900 (A. awamori) (A. awamori) Linker which from gluco- plus 5' 1/2 end codes for Kex2 lase of gluco- peptidase (A. niger) amylase gene cleavage site (A. awamori)__________________________________________________________________________
EXAMPLE 8
PRODUCTION OF LACTOFERRIN USING PUBLISHED DNA SEQUENCES WHICH CONTAIN ALLERGIC VARIATIONS
One may employ any one of several known DNA sequences encoding for lactoferrins as identified in the published literature and patent applications referenced above, incorporated herein by reference. Additionally, one may employ DNA sequences encoding polypeptide fragments of lactoferrin which maintain characteristics of lactoferrin. One of ordinary skill in this art will understand and know that the scope of this invention also includes the production of the different published and obvious therefrom allergic variants of human, porcine or bovine lactoferrin. Some allergic variations have been reported in the literature and they are intended to be included as the types of lactoferrins that may be produced by the process of the subject invention.
EXAMPLE 9
FERMENTATION PROTOCOLS
Different growth and production conditions can be used for the expression of recombinant human lactoferrin in Aspergillus awamori. The following descriptions are presented for the purposes of illustrating various conditions which can be used for the expression of hLF in Aspergillus awamori and are not meant to be limitations of the present invention in any form. Presented below is a general outline of the fermentation production process and the process used to recover the produced lactoferrin. One of ordinary skill in this art understands that the protocol may be changed or modified in minor ways in order to enhance the production of the desired lactoferrin or lactoferrin polypeptide.
The following is a brief outline for producing lactoferrin by using a fermentation process.
I. FERMENTATION PROCESS
A. MEDIUM COMPONENTS
______________________________________1) Seed medium______________________________________ Roquette Corn Steep Powder 100 g/L Glucose 10 g/L7H.sub.2 OMgSO.sub.4 1 g/L2H.sub.2 ONaH.sub.2 PO.sub.4 1 g/L______________________________________
pH to 5.8 before autoclaving and autoclave for 15 minutes.
______________________________________ Production medium2. (concentrations are post-inoculation)______________________________________ Amaizo Lodex-5 partially 175 g/L Hydrolyzed corn starch Roquette Corn Steep Powder (Solulys .RTM. A ST) 60 g/L Trisodium Citrate 80 g/L7H.sub.2 OSO.sub.4 2 g/L2H.sub.2 OH.sub.2 PO.sub.4 1.3 g/L Ammonium sulfate 15 g/L Antifoam 204 2 ml/L______________________________________
pH to 6.2 before autoclaving and autoclave for 15 minutes.
The inventors have found that enhanced lactoferrin production can be achieved when partially hydrolyzed starches are used in the fermentation process. However, combinations of unmodified corn starch and dextrose have yielded reasonable production of lactoferrin. One may employ less amounts of starch products or substitute more expensive starch products to optimize production of the lactoferrin by routine experimentation.
B. FERMENTATION PROCESS
To date, the fermentation is run as a batch process. Maximum product concentration is reached at 5-6 days.
1) Seed stage 1:
a) 450 mls of seed medium in a 2 L Erlenmeyer flask
b) Inoculate with 1.times.10.sup.6 spores per ml of seed medium.
c) Incubate for 24 hours at 33.degree. C., 70% relative humidity at 240 rpm (50 mm throw shaker).
2) Seed stage 2:
a) 20 L seed medium in a NBS Micros 30 fermenter with two 12 cm six-blade rushton impellers.
b) 30 minute sterilization.
Inoculate with 2% of stage 1 seed.
______________________________________ Agitation 500 rpm Airflow 0.75 VVM Pressure 300 mbar pH not controlled DO not controlled______________________________________
3) Production:
The pilot vessel is a B. Braun Biotech UD100 with a 3:1 aspect ratio. Two 16 cm six-blade Rushton impellers are used for agitation. The fermentation is run at 80 L post-inoculation.
______________________________________Agitation 450 rpm Power input has not yet been examined.Temperature 33.degree. C.Aeration 0.75 VVM This variable has not yet been examined.Pressure 300 mbarPH Not controlledDO Not controlled This variable has not yet been examined.Antifoam Not required______________________________________
Vessel conditions are as described above. Vessel is charged with 80 L of Medium Components and brought to a volume of 72 L with deionized water. It is sterilized for 30 minutes. Eight liters (10% CV) of Stage 2 seed is transferred at 36-48 hours growth. Optimized seed processes are currently being developed.
Lactoferrin production is seen by 24 hours with maximum product accumulation at 5-6 days.
II. DOWNSTREAM PROCESSING
A. FILTRATION
The fermentation reaches a 30-40% packed cell volume with a non-pelleted morphology. If filtration is used to clarify the broth, a filter aid is required. Because of the low process volumes, straight vacuum filtration over a 3,000 cm.sup.2 support may be used. A polypropylene filter mat is used as a base.
Initial tests used diatomaceous earth as the filter aid. However, straight-calcined or flux-calcined diatomaceous earth cannot be used as a filter aid as they bind lactoferrin. Only acid-washed diatomaceous earth will not bind lactoferrin. Acid-washed diatomaceous earth (DE) can be purchased at 40-50 times the cost of the untreated product. Another option is to acid wash the DE at the production site. Preliminary tests determined that it can be slurried with 3N HCl, mixed for 45 minutes and then washed with deionized water until the wash water is pH 4.0. Lactoferrin did not bind to this treated material. The treated DE was used at a 1:5 W/V ratio with whole broth. The DE was slurried with deionized water prior to mixing with the broth. It was found that a 1:10 ratio did not allow filtration.
An alternative product is cellulose fiber. The inventors have found that Solkafloc 10IND (Protein Technologies International in Urbana, Ill.; 1-800-258-0351) works well with no binding of lactoferrin. The inventors use Solkafloc as a filler to aid filtration. For 100 L of fermentation broth, 20 kg of Solkafloc is slurried with 100 L of deionized water. The broth is mixed into the slurry. The mixture is then filtered easily. The clarity achieved at this step enables further downstream processing (ultrafiltration and column chromatography) to proceed without additional filtration requirements. The ratio of Solkafloc to broth and deionized water for a single batch filtration is in the process of being optimized. Recovery of lactoferrin should almost be quantitative if the filter cake is washed. With continuous filtration process equipment, the methods for using Solkafloc as a filter aid will change.
One may use existing strains or develop strains with improved rheology and filtration characteristics. For example, mutants that pellet in stirred tank fermentation will allow thicker filter cakes during processing and will not require filter aid except as a filter precoat.
B. ULTRAFILTRATION
The clarified broth is concentrated using ultrafiltration. Two Amicon S10Y30 (0.93 m.sup.2 each) spiral cartridges with 30,000 MW membranes are used with an Amicon DC-30 system. The membranes are a low protein-binding cellulose-based material. Flux rates are 1-1.8 rpm depending on the stage of the process. Once a minimum operational process volume has been reached, the concentrated solution is continuously dialyzed with five volumes of a buffer containing 0.1 M NaCl, 1mM EDTA, and 25 mM TRIS pH 7.5. The buffer is then cooled to 4.degree. C. and the dialyzed solution is concentrated to the minimum volume possible and recovered. Yields have been near 100% with this process.
The final ultrafiltration (UF) concentrate is 5-8 mg/ml total protein with lactoferrin at 10% of total protein. The recovery rate will be optimized as new strains are developed. For an 80 L fermentation batch, concentration and dialysis with this system takes approximately 2 hours.
C. CHROMATOGRAPHIC SEPARATION
Pharmacia CM Sepharose Fast Flow gel is used. The binding capacity of this resin for lactoferrin in clarified broth is approximately 20 mg/ml.
UF concentrate is applied to the column. The loaded column is washed first with 0.1 M NaCl/25 mM TRIS pH 7.5, and then with a 0.2M NaCl 25 mM TRIS pH 7.5. No lactoferrin will be released unless the column is overloaded. The lactoferrin is eluted with 0.5M NaCl/25 mM TRIS pH 7.5. The volume of the elution fractions containing lactoferrin is usually twice the volume of the resin bed.
D. CONVERSION TO APOLACTOFERRIN
The 0.5M NaCl fractions containing lactoferrin are combined. 1M ammonium citrate is added to bring the final concentration to 0.1M ammonium citrate. The pH is slowly adjusted to 2.0 with 10 N HCl. The solution is transferred to an appropriately sized ultrafiltration unit using 30,000 MW membranes where it is concentrated to an appropriate volume and then continuously dialyzed with five volumes of 0.5M NaCl/0.1M Ammonium citrate pH 2.0. After release and dialysis of iron is completed, the pH is adjusted to neutral to prevent precipitation in the next process. If there is residual iron present, it will rebind to the lactoferrin at the neutral pH. The dialysis buffer is changed to 50 mM ammonium bicarbonate (pH 7.8) and the solution is continuously dialyzed with five volumes of buffer. The solution is then concentrated to a minimum volume, recovered, and lyophilized.
The procedure is currently being optimized. Specific factors are considered on a case by case basis depending on the strain used. Some of the factors include (1) pH limits, (2) pre-treatment of equipment to eliminate iron, and (3) pre-treatment of buffers with Chelex resins to remove trace amounts of iron. It may be necessary to go through an intermediate buffer such as 0.2M NaCl 50 mM Ammonium bicarbonate to avoid precipitation of lactoferrin and rebinding of residual iron.
EXAMPLE 10
PRODUCTION OF LACTOFERRIN OR LACTOFERRIN POLYPEPTIDE FRAGMENTS AS A FUSION PRODUCT IN ASPERGILLUS ORYZAE OR ASPERGILLUS NIGER CELLS
A Expression of Lactoferrin or Lactoferrin Polypeptide Fragments in Asvergillus Orazae.
A similar expression vector as that which has been previously described can be constructed to allow for the expression of lactoferrin or lactoferrin polypeptide fragments as a fusion protein product in Aspergillus oryzae. The A. oryzae expression vector would contain the following components operably linked from 5' to 3':
(a) a promoter from the promoter from Aspergillus oryzae .alpha.-amylase gene;
(b) signal sequence from the A. oryzae .alpha.-amylase gene;
(c) 5' portion of the A. oryzae .alpha.-amylase gene;
(d) linker sequence encoding Kex2 peptidase cleavage site whereby there is an endogenous proteolytic enzyme specific for said linker sequence;
(e) transcription termination sequence from the A. niger glucoamylase gene; and
(f) phleomycin resistance selectable marker gene;
wherein said vector is capable of producing lactoferrin or a lactoferrin polypeptide fragment as a fusion protein and expressing the same as a processed protein.
The vector would then be used to transform A. oryzae cells; the product of this novel plasmid vector construct is a fusion protein comprised of half of the highly expressed A. oryzae .alpha.-amylase gene fused to the lactoferrin or lactoferrin polypeptide fragment corresponding to the nucleotide sequence of step (e) above. The lactoferrin or lactoferrin polypeptide fragment fusion product would then be processed by an endogenous A. oryzae proteolytic enzyme which is specific for the Kex2 peptidase site.
B. Expression of Lactoferrin or Lactoferrin Polypeptide Fragments in Aspergillus Niger
A similar expression vector as that which has been previously described can be constructed to allow for the expression of lactoferrin or lactoferrin polypeptide fragments as a fusion protein product in Aspergillus niger. The A. niger expression vector would contain the following components operably linked from 5' to 3':
(a) promoter from Aspergillus niger glucoamylase gene;
(b) signal sequence from the A. niger glucoamylase gene;
(c) 5' portion of the A. niger glucoamylase gene;
(d) linker sequence encoding Kex2 peptidase cleavage site whereby there is an endogenous proteolytic enzyme specific for said linker sequence;
(e) transcription termination sequence from the A. niger glucoamylase gene; and
(f) phleomycin resistance selectable marker gene;
wherein said vector is capable of producing lactoferrin or a lactoferrin polypeptide fragment as a fusion protein and expressing the same as a processed protein.
The vector would then be used to transform A. niger cells; the product of this novel plasmid vector construct is a fusion protein comprised of half of the highly expressed A. niger glycoamylase gene fused to the lactoferrin or lactoferrin polypeptide fragment corresponding to the nucleotide sequence of step (e) above. The lactoferrin or lactoferrin polypeptide fragment fusion product would then be processed by an endogenous A. niger proteolytic enzyme which is specific for the Kex2 peptidase site.
In conclusion, it is seen that the present invention and the embodiments disclosed herein are well adapted to carry out the objectives and obtain the end set forth in this application. Certain changes can be made in the method and apparatus without parting from the spirit and scopes of this invention. It is realized that changes are possible and that it is further intended that each element or step presided in any of the filing claims is to be understood as to referring to all equivalent elements or steps for accomplishing the essentially the same results in substantially the same or equivalent manner. It is intended to cover the invention broadly in whatever form its principles may be utilized. The present invention, therefore, is well adapted to carry out the objects and obtain the ends and advantages mentioned, as well as others inherent therein.
__________________________________________________________________________# SEQUENCE LISTING- (1) GENERAL INFORMATION:- (iii) NUMBER OF SEQUENCES: 8- (2) INFORMATION FOR SEQ ID NO:1:- (i) SEQUENCE CHARACTERISTICS:#pairs (A) LENGTH: 32 base (B) TYPE: nucleic acid (C) STRANDEDNESS: single (D) TOPOLOGY: linear- (iii) HYPOTHETICAL: NO- (iv) ANTI-SENSE: NO- (xi) SEQUENCE DESCRIPTION: SEQ ID NO:1:# 32 CGTA GGAGAAGGAG TG- (2) INFORMATION FOR SEQ ID NO:2:- (i) SEQUENCE CHARACTERISTICS:#pairs (A) LENGTH: 25 base (B) TYPE: nucleic acid (C) STRANDEDNESS: single (D) TOPOLOGY: linear- (iii) HYPOTHETICAL: NO- (iv) ANTI-SENSE: NO- (xi) SEQUENCE DESCRIPTION: SEQ ID NO:2:# 25 TCCG CCGCT- (2) INFORMATION FOR SEQ ID NO:3:- (i) SEQUENCE CHARACTERISTICS:#pairs (A) LENGTH: 24 base (B) TYPE: nucleic acid (C) STRANDEDNESS: single (D) TOPOLOGY: linear- (iii) HYPOTHETICAL: NO- (iv) ANTI-SENSE: NO- (xi) SEQUENCE DESCRIPTION: SEQ ID NO:3:# 24CCCC TGAC- (2) INFORMATION FOR SEQ ID NO:4:- (i) SEQUENCE CHARACTERISTICS:#pairs (A) LENGTH: 32 base (B) TYPE: nucleic acid (C) STRANDEDNESS: single (D) TOPOLOGY: linear- (iii) HYPOTHETICAL: NO- (iv) ANTI-SENSE: NO- (xi) SEQUENCE DESCRIPTION: SEQ ID NO:4:# 32 CCTG TGCAGACGAG GC- (2) INFORMATION FOR SEQ ID NO:5:- (i) SEQUENCE CHARACTERISTICS:#pairs (A) LENGTH: 19 base (B) TYPE: nucleic acid (C) STRANDEDNESS: single (D) TOPOLOGY: linear- (iii) HYPOTHETICAL: NO- (iv) ANTI-SENSE: NO- (xi) SEQUENCE DESCRIPTION: SEQ ID NO:5:# 19 GCT- (2) INFORMATION FOR SEQ ID NO:6:- (i) SEQUENCE CHARACTERISTICS:#pairs (A) LENGTH: 39 base (B) TYPE: nucleic acid (C) STRANDEDNESS: single (D) TOPOLOGY: linear- (iii) HYPOTHETICAL: NO- (iv) ANTI-SENSE: NO#ID NO:6: (xi) SEQUENCE DESCRIPTION: SEQ#39 GCAA GAATGTGATT TCCAAGCGC- (2) INFORMATION FOR SEQ ID NO:7:- (i) SEQUENCE CHARACTERISTICS:#pairs (A) LENGTH: 39 base (B) TYPE: nucleic acid (C) STRANDEDNESS: single (D) TOPOLOGY: linear- (iii) HYPOTHETICAL: NO- (iv) ANTI-SENSE: NO#ID NO:7: (xi) SEQUENCE DESCRIPTION: SEQ#39 CGTT CTTACACTAA AGGTTCGCG- (2) INFORMATION FOR SEQ ID NO:8:- (i) SEQUENCE CHARACTERISTICS:#pairs (A) LENGTH: 21 base (B) TYPE: nucleic acid (C) STRANDEDNESS: single (D) TOPOLOGY: linear- (iii) HYPOTHETICAL: NO- (iv) ANTI-SENSE: NO#ID NO:8: (xi) SEQUENCE DESCRIPTION: SEQ# 21 AAGG A__________________________________________________________________________

Number	Name	Date
4652639	Stabinsky	Mar 1987
4703008	Lin	Oct 1987
4710465	Weissman et al.	Dec 1987
4766075	Goeddel et al.	Aug 1988
4886747	Derynck et al.	Dec 1989
4959318	Foster et al.	Sep 1990
4965190	Woo et al.	Oct 1990
5019508	Johnson et al.	May 1991
5081227	Millan	Jan 1992
5304633	Tomita et al.	Apr 1994
5571691	Conneely et al.	Nov 1996
5571697	Conneely et al.	Nov 1996
5571896	Conneely et al.	Nov 1996

Number	Date	Country
WO9105045	Apr 1991	WOX
WO9113982	Sep 1991	WOX

	Number	Date
Parent	691123	Aug 1996
Parent	303009	Nov 1994
Parent	348270	May 1989
Parent	250308	May 1994

	Number	Date
Parent	145681	Oct 1993
Parent	967947	Oct 1992
Parent	873304	Apr 1992

Expression of processed recombinant lactoferrin and lactoferrin polypeptide fragments from a fusion product in Aspergillus

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US Referenced Citations (13)

Foreign Referenced Citations (2)

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Entry
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