Patent Application
20170080077
This invention is in the field of protein expression. In particular, it relates to the heterologous expression of proteins from Neisseria (e.g. N. gonorrhoeae or, preferably, N. meningitidis).
The content of the following submission on ASCII text file is incorporated herein by reference in its entirety: a computer readable form (CRF) of the Sequence Listing (file name: 303822001_004 SegList.txt, date recorded: Nov. 29, 2016, size: 405 KB).
International patent applications WO99/24578, WO99/36544, WO99/57280 and WO00/22430 disclose proteins from Neisseria meningitidis and Neisseria gonorrhoeae. These proteins are typically described as being expressed in E. coli (i.e. heterologous expression) as either N-terminal GST-fusions or C-terminal His-tag fusions, although other expression systems, including expression in native Neisseria, are also disclosed.
It is an object of the present invention to provide alternative and improved approaches for the heterologous expression of these proteins. These approaches will typically affect the level of expression, the ease of purification, the cellular localisation of expression, and/or the immunological properties of the expressed protein.
The 2166 protein sequences disclosed in WO99/24578, WO99/36544 and WO99/57280 are referred to herein by the following SEQ# numbers:
In addition to this SEQ# numbering, the naming conventions used in WO99/24578, WO99/36544 and WO99/57280 are also used (e.g. ‘ORF4’, ‘ORIF40’, ‘ORF40-1’ etc. as used in WO99/24578 and WO99/36544; ‘m919’, ‘g919’ and ‘a919’ etc. as used in WO99/57280).
The 2160 proteins NMB0001 to NMB2160 from Tettelin et al. [Science (2000) 287:1809-1815] are referred to herein as SEQ4#s 21674326 [see also WO00/66791].
The term ‘protein of the invention’ as used herein refers to a protein comprising:
The degree of ‘sequence identity’ referred to in (b) is preferably greater than 50% (eg. 60%, 70%, 80%, 90%, 95%, 99% or more). This includes mutants and allelic variants [e.g. see WO00/66741]. Identity is preferably determined by the Smith-Waterman homology search algorithm as implemented in the MPSRCH program (Oxford Molecular), using an affine gap search with parameters gap open penalty=12 and gap extension penalty=1. Typically, 50% identity or more between two proteins is considered to be an indication of functional equivalence.
The ‘fragment’ referred to in (c) should comprise at least n consecutive amino acids from one of SEQ#s 1-4326 and, depending on the particular sequence, n is 7 or more (eg. 8, 10, 12, 14, 16, 18, 20, 25, 30, 35, 40, 50, 60, 70, 80, 90, 100 or more). Preferably the fragment comprises an epitope from one of SEQ#s 14326. Preferred fragments are those disclosed in WO00/71574 and WO01/04316.
Preferred proteins of the invention are found in N. meningitidis serogroup B.
Preferred proteins for use according to the invention are those of serogroup B N. meningitidis strain 2996 or strain 394198 (a New Zealand strain). Unless otherwise stated, proteins mentioned herein are from N. meningitidis strain 2996. It will be appreciated, however, that the invention is not in general limited by strain. References to a particular protein (e.g. ‘287’, ‘919’ etc.) may be taken to include that protein from any strain.
In a first approach to heterologous expression, no fusion partner is used, and the native leader peptide (if present) is used. This will typically prevent any ‘interference’ from fusion partners and may alter cellular localisation and/or post-translational modification and/or folding in the heterologous host.
Thus the invention provides a method for the heterologous expression of a protein of the invention, in which (a) no fusion partner is used, and (b) the protein's native leader peptide (if present) is used.
The method will typically involve the step of preparing an vector for expressing a protein of the invention, such that the first expressed amino acid is the first amino acid (methionine) of said protein, and last expressed amino acid is the last amino acid of said protein (i.e. the codon preceding the native STOP codon).
This approach is preferably used for the expression, of the following proteins using the native leader peptide: 111, 149, 206, 2254, 235, 247-1, 274, 283, 286, 292, 401, 406, 502-1, 503, 519-1, 525-1, 552, 556, 557, 570, 576-1, 580, 583, 664, 759, 907, 913, 920-1, 936-1, 953, 961, 983, 989, Orf4, Orf7-1, Orf9-1, Orf23, Orf25, Orf37, Orf38, Orf40, Orf40.1, Orf40.2, Orf72-1, Orf76-1, Orf85-2, Orf91, Orf97-1, Orf119, Orf143.1, NMB0109 and NMB2050. The suffix ‘L’ used herein in the name of a protein indicates expression in this manner using the native leader peptide.
Proteins which are preferably expressed using this approach using no fusion partner and which have no native leader peptide include: 008, 105, 117-1, 121-1, 122-1, 128-1, 148, 216, 243, 308, 593, 652, 726, 926, 982, Orf83-1 and Orf143-1.
Advantageously, it is used for the expression of ORF25 or ORF40, resulting in a protein which induces better anti-bactericidal antibodies than GST- or His-fusions.
This approach is particularly suited for expressing lipoproteins.
In a second approach to heterologous expression, the native leader peptide of a protein of the invention is replaced by that of a different protein. In addition, it is preferred that no fusion partner is used. Whilst using a protein's own leader peptide in heterologous hosts can often localise the protein to its ‘natural’ cellular location, in some cases the leader sequence is not efficiently recognised by the heterologous host. In such cases, a leader peptide known to drive protein targeting efficiently can be used instead.
Thus the invention provides a method for the heterologous expression of a protein of the invention, in which (a) the protein's leader peptide is replaced by the leader peptide from a different protein and, optionally, (b) no fusion partner is used.
The method will typically involve the steps of: obtaining nucleic acid encoding a protein of the invention; manipulating said nucleic acid to remove nucleotides that encode the protein's leader peptide and to introduce nucleotides that encode a different protein's leader peptide. The resulting nucleic acid may be inserted into an expression vector, or may already be part of an expression vector. The expressed protein will consist of the replacement leader peptide at the N-tertninus, followed by the protein of the invention minus its leader peptide.
The leader peptide is preferably from another protein of the invention (e.g. one of SEQ#s 1-4326), but may also be from an E. coli protein (e.g. the OmpA leader peptide) or an Erwinia carotovora protein (e.g. the PelB leader peptide), for instance.
A particularly useful replacement leader peptide is that of ORF4. This leader is able to direct lipidation in E. coli, improving cellular localisation, and is particularly useful for the expression of proteins 287, 919 and ΔG287. The leader peptide and N-terminal domains of 961 are also particularly useful.
Another useful replacement leader peptide is that of E. coli OmpA. This leader is able to direct membrane localisation of E. coli. It is particularly advantageous for the expression of ORF1, resulting in a protein which induces better anti-bactericidal antibodies than both fusions and protein expressed from its own leader peptide.
Another useful replacement leader peptide is MICKYLFSAA. This can direct secretion into culture medium, and is extremely short and active. The use of this leader peptide is not restricted to the expression of Neisserial proteins—it may be used to direct the expression of any protein (particularly bacterial proteins).
In a third approach to heterologous expression, the native leader peptide of a protein of the invention is deleted. In addition, it is preferred that no fusion partner is used.
Thus the invention provides a method for the heterologous expression of a protein of the invention, in which (a) the protein's leader peptide is deleted and, optionally, (b) no fusion partner is used.
The method will typically involve the steps of: obtaining nucleic acid encoding a protein of the invention; manipulating said nucleic acid to remove nucleotides that encode the protein's leader peptide. The resulting nucleic acid may be inserted into an expression vector, or may already be part of an expression vector. The first amino acid of the expressed protein will be that of the mature native protein.
This method can increase the levels of expression. For protein 919, for example, expression levels in E. coli are much higher when the leader peptide is deleted. Increased expression may be due to altered localisation in the absence of the leader peptide.
The method is preferably used for the expression of 919, ORF46, 961, 050-1, 760 and 287.
In a fourth approach to heterologous expression, the protein is expressed as domains. This may be used in association with fusion systems (e.g. GST or His-tag fusions).
Thus the invention provides a method for the heterologous expression of a protein of the invention, in which (a) at least one domain in the protein is deleted and, optionally, (b) no fusion partner is used.
The method will typically involve the steps of: obtaining nucleic acid encoding a protein of the invention; manipulating said nucleic acid to remove at least one domain from within the protein. The resulting nucleic acid may be inserted into an expression vector, or may already be part of an expression vector. Where no fusion partners are used, the first amino acid of the expressed protein will be that of a domain of the protein.
A protein is typically divided into notional domains by aligning it with known sequences in databases and then determining regions of the protein which show different alignment patterns from each other.
The method is preferably used for the expression of protein 287. This protein can be notionally split into three domains, referred to as A B & C (see
Once a protein has been divided into domains, these can be (a) expressed singly (b) deleted from with the protein e.g. protein ABCD→ABD, ACD, BCD etc, or (c) rearranged e.g. protein ABC→ACB, CAB etc. These three strategies can be combined with fusion partners is desired.
ORF46 has also been notionally split into two domains a first domain (amino acids 1-433) which is well-conserved between species and serogroups, and a second domain (amino acids 433-608) which is not well-conserved. The second domain is preferably deleted. An alignment of polymorphic forms of ORF46 is disclosed in WO00/66741.
Protein 564 has also been split into domains (
In a fifth approach to heterologous expression, two or more (e.g. 3, 4, 5, 5 or more) proteins of the invention are expressed as a single hybrid protein. It is preferred that no non-Neisserial fusion partner (e.g. GST or poly-His) is used.
This offers two advantages. Firstly, a protein that may be unstable or poorly expressed on its own can be assisted by adding a suitable hybrid partner that overcomes the problem. Secondly, commercial manufacture is simplified only one expression and purification need be employed in order to produce two separately-useful proteins.
Thus the invention provides a method for the simultaneous heterologous expression of two or more proteins of the invention, in which said two or more proteins of the invention are fused (i.e. they are translated as a single polypeptide chain).
The method will typically involve the steps of obtaining a first nucleic acid encoding a first protein of the invention; obtaining a second nucleic acid encoding a second protein of the invention; ligating the first and second nucleic acids. The resulting nucleic acid may be inserted into an expression vector, or may already be part of an expression vector.
Preferably, the constituent proteins in a hybrid protein according to the invention will be from the same strain.
The fused proteins in the hybrid may be joined directly, or may be joined via a linker peptide e.g. via a poly-glycine linker (i.e. G where n=3, 4, 5, 6, 7, 8, 9, 10 or more) or via a short peptide sequence which facilitates cloning. It is evidently preferred not to join a ΔG protein to the C-terminus of a poly-glycine linker.
The fused proteins may lack native leader peptides or may include the leader peptide sequence of the N-terminal fusion partner.
The method is well suited to the expression of proteins orf1, orf4, orf25, orf40, Orf46/46.1, orf83, 233, 287, 292L, 564, 687, 741, 907, 919, 953, 961 and 983.
The 42 hybrids indicated by ‘X’ in the following table of form NH2-A-B-COOH are preferred:
Preferred proteins to be expressed as hybrids are thus ORF46.1, 287, 741, 919, 953, 961 and 983. These may be used in their essentially full-length form, or poly-glycine deletions (ΔG) forms may be used (e.g. ΔG-287, ΔGTbp2, ΔG741, ΔG983 etc.), or truncated forms may be used (e.g. Δ1-287, Δ2-287 etc.), or domain-deleted versions may be used (e.g. 287B, 287C, 287BC, ORP461-433, ORF46433-608, ORF46, 961c etc.).
Particularly preferred are: (a) a hybrid protein comprising 919 and 287; (b) a hybrid protein comprising 953 and 287; (c) a hybrid protein comprising 287 and ORF46.1; (d) a hybrid protein comprising ORF1 and ORF46.1; (e) a hybrid protein comprising 919 and ORF46.1; (1) a hybrid protein comprising ORF46.1 and 919; (g) a hybrid protein comprising ORF46.1, 287 and 919; (h) a hybrid protein comprising 919 and 519; and (1) a hybrid protein comprising ORF97 and 225. Further embodiments are shown in
Where 287 is used, it is preferably at the C-terminal end of a hybrid; if it is to be used at the N-terminus, if is preferred to use a ΔG form of 287 is used (e.g. as the N-terminus of a hybrid with ORF46.1, 919, 953 or 961).
Where 287 is used, this is preferably from strain 2996 or from strain 394/98.
Where 961 is used, this is preferably at the N-terminus. Domain forms of 961 may be used.
Alignments of polymorphic forms of ORF46, 287, 919 and 953 are disclosed in WO00/66741, Any of these polymorphs can be used according to the present invention.
In a sixth approach to heterologous expression, proteins of the invention are expressed at a low temperature.
Expressed Neisserial proteins (e.g. 919) may be toxic to E. coli, which can be avoided by expressing the toxic protein at a temperature at which its toxic activity is not manifested.
Thus the present invention provides a method for the heterologous expression of a protein of the invention, in which expression of a protein of the invention is carried out at a temperature at which a toxic activity of the protein is not manifested.
A preferred temperature is around 30° C. This is particularly suited to the expression of 919.
As discussed above, expressed Neisserial proteins may be toxic to E. coli. This toxicity can be avoided by mutating the protein to reduce or eliminate the toxic activity. In particular, mutations to reduce or eliminate toxic enzymatic activity can be used preferably using site-directed mutagenesis.
In a seventh approach to heterologous expression, therefore, an expressed protein is mutated to reduce or eliminate toxic activity.
Thus the invention provides a method for the heterologous expression of a protein of the invention, in which protein is mutated to reduce or eliminate toxic activity.
The method is preferably used for the expression of protein 907, 919 or 922. A preferred mutation in 907 is at Glu-117 (e.g. Glu→Gly); preferred mutations in 919 are at Glu-255 (e.g. Glu→Gly) and/or Glu-323 (e.g. Glu→Gly); preferred mutations in 922 are at Glu-164 (e.g. Glu→Gly), Ser-213 (e.g. Ser→Gly) and/or Asn-348 (e.g. Asn→Gly).
In a eighth approach to heterologous expression, an alternative vector used to express the protein. This may be to improve expression yields, for instance, or to utilise plasmids that are already approved for GMP use.
Thus the invention provides a method for the heterologous expression of a protein of the invention, in which an alternative vector is used. The alternative vector is preferably pSM214, with no fusion partners. Leader peptides may or may not be included.
This approach is particularly useful for protein 953. Expression and localisation of 953 with its native leader peptide expressed from pSM214 is much better than from the pET vector.
pSM214 may also be used with: ΔG287, Δ2-287, Δ3-287, Δ4-287, Orf46.1, 961L, 961, 961(MC58), 961c, 961c-L, 919, 953 and ΔG287-Orf46.1.
Another suitable vector is pET-24b (Novagen; uses kanamycin resistance), again using no fusion partners. pET-24b is preferred for use with: ΔG287K, Δ2-287K, Δ3-287K, Δ4-287K, Orf46.1-K, Orf46A-K, 961-K (MC58), 961a-K, 961b-K, 961c-K, 961c-L-K, 961d-K, ΔG287-919-K, ΔG287-Orf46.1-K and ΔG287-961-K.
In a ninth approach to heterologous expression, a protein is expressed or purified such that it adopts a particular multimeric form.
This approach is particularly suited to protein 953. Purification of one particular multimeric form of 953 (the monomeric form) gives a protein with greater bactericidal activity than other forms (the dimeric form).
Proteins 287 and 919 may be purified in dimeric forms.
Protein 961 may be purified in a 180 kDa oligomeric form (e.g. a tetramer).
In a tenth approach to heterologous expression, a protein is expressed as a lipidated protein.
Thus the invention provides a method for the heterologous expression of a protein of the invention, in which the protein is expressed as a lipidated protein.
This is particularly useful for the expression of 919, 287, ORF4, 406, 576-1, and ORF25. Polymorphic forms of 919, 287 and ORF4 are disclosed in WO00/66741.
The method will typically involve the use of an appropriate leader peptide without using an N-terminal fusion partner.
In an eleventh approach to heterologous expression, the C-terminus of a protein of the invention is mutated. In addition, it is preferred that no fusion partner is used.
Thus the invention provides a method for the heterologous expression of a protein of the invention, in which (a) the protein's C-terminus region is mutated and, optionally, (b) no fusion partner is used.
The method will typically involve the steps of: obtaining nucleic acid encoding a protein of the invention; manipulating said nucleic acid to mutate nucleotides that encode the protein's C-terminus portion. The resulting nucleic acid may be inserted into an expression vector, or may already be part of an expression vector. The first amino acid of the expressed protein will be that of the mature native protein.
The mutation may be a substitution, insertion or, preferably, a deletion.
This method can increase the levels of expression, particularly for proteins 730, ORF29 and ORF46. For protein 730, a C-terminus region of around 65 to around 214 amino acids may be deleted; for ORF46, the C-terminus region of around 175 amino acids may be deleted; for ORF29, the C-terminus may be deleted to leave around 230-370 N-terminal amino acids.
In a twelfth approach to heterologous expression, the leader peptide of the protein is mutated. This is particularly useful for the expression of protein 919.
Thus the invention provides a method for the heterologous expression of a protein of the invention, in which the protein's leader peptide is mutated.
The method will typically involve the steps of: obtaining nucleic acid encoding a protein of the invention; and manipulating said nucleic acid to mutate nucleotides within the leader peptide. The resulting nucleic acid may be inserted into an expression vector, or may already be part of an expression vector.
In a thirteenth approach to heterologous expression, poly-glycine stretches in wild-type sequences are mutated. This enhances protein expression.
The poly-glycine stretch has the sequence (Gly)n, where n≧4 (e.g. 5, 6, 7, 8, 9 or more). This stretch is mutated to disrupt or remove the (Gly)n. This may be by deletion (e.g. CGGGGS→CGGGS, COGS, CGS or CS), by substitution (e.g. CGCGGS→CGXGGS, CGCXGS, CGXGXS etc.), and/or by insertion (e.g. CGGGGS→CGGXGGS, CGXGOGS, etc.
This approach is not restricted to Neisserial proteins—it may be used for any protein (particularly bacterial proteins) to enhance heterologous expression. For Neisserial proteins, however, it is particularly suitable for expressing 287, 741, 983 and Thp2. An alignment of polymorphic forms of 287 is disclosed in WO00/66741.
Thus the invention provides a method for the heterologous expression of a protein of the invention, in which (a) a poly-glycine stretch within the protein is mutated.
The method will typically involve the steps of: obtaining nucleic acid encoding a protein of the invention; and manipulating said nucleic acid to mutate nucleotides that encode a poly-glycine stretch within the protein sequence. The resulting nucleic acid may be inserted into an expression vector, or may already be part of an expression vector.
Conversely, the opposite approach (i.e. introduction of poly-glycine stretches) can be used to suppress or diminish expression of a given heterologous protein.
Whilst expression of the proteins of the invention may take place in the native host (i.e. the organism in which the protein is expressed in nature), the present invention utilises a heterologous host. The heterologous host may be prokaryotic or eukaryotic. It is preferably E. coli, but other suitable hosts include Bacillus subtilis, Vibrio cholerae, Salmonella typhi, Salmonenna typhimurium, Neisseria meningitidis, Neisseria gonorrhoeae, Neisseria lactarnica, Neisseria cinerea, Mycobateria (e.g. M. tuberculosis), yeast etc.
As well as the methods described above, the invention provides (a) nucleic acid and vectors useful in these methods (b) host cells containing said vectors (c) proteins expressed or expressable by the methods (d) compositions comprising these proteins, which may be suitable as vaccines, for instance, or as diagnostic reagents, or as immunogenic compositions (e) these compositions for use as medicaments (e.g. as vaccines) or as diagnostic reagents (f) the use of these compositions in the manufacture of (1) a medicament for treating or preventing infection due to Neisserial bacteria (2) a diagnostic reagent for detecting the presence of Neisserial bacteria or of antibodies raised against Neisserial bacteria, and/or (3) a reagent which can raise antibodies against Neisserial bacteria and (g) a method of treating a patient, comprising administering to the patient a therapeutically effective amount of these compositions.
The invention also provides a protein or a nucleic acid having any of the sequences set out in the following examples. It also provides proteins and nucleic acid having sequence identity to these. As described above, the degree of ‘sequence identity’ is preferably greater than 50% (eg. 60%, 70%, 80%, 90%, 95%, 99% or more).
Furthermore, the invention provides nucleic acid which can hybridise to the nucleic acid disclosed in the examples, preferably under “high stringency” conditions (eg. 65° C. in a 0.1×SSC, 0.5% SDS solution).
The invention also provides nucleic acid encoding proteins according to the invention.
It should also be appreciated that the invention provides nucleic acid comprising sequences complementary to those described above (eg, for antisense or probing purposes).
Nucleic acid according to the invention can, of course, be prepared in many ways (eg. by chemical synthesis, from genomic or cDNA libraries, from the organism itself etc.) and can take various forms (eg. single stranded, double stranded, vectors, probes etc.).
In addition, the term “nucleic acid” includes DNA and RNA, and also their analogues, such as those containing modified backbones, and also peptide nucleic acids (PNA) etc.
Protein 919 from N. meningitidis (serogroup B, strain 2996) has the following sequence:
MKKYLFRAAL YGLAAAILAA CQSKSIQTFP QPDTSVINGP DRPVGIPDPA
The leader peptide is underlined.
The sequences of 919 from other strains can be found in FIGS. 7 and 18 of WO00/667411.
Example 2 of WO99/57280 discloses the expression of protein 919 as a His-fusion in E. coli. The protein is a good surface-exposed immunogen.
Three alternative expression strategies were used for 919:
MKTFFKTLS AAALALILAA CQSKSIQTFP QPDTSVINGP DRPVGIPDPA
All three forms of the protein were expressed and could be purified.
The ‘919’ and ‘919LOrf4’ expression products were both lipidated, as shown by the incorporation of [3H]-palmitate label. 919untagged did not incorporate the 3H label and was located intracellularly.
919LOrf4 could be purified more easily than 919L. It was purified and used to immunise mice. The resulting sera gave excellent results in FACS and ELISA tests, and also in the bactericidal assay. The lipoprotein was shown to be localised in the outer membrane.
919untagged gave excellent ELISA titres and high serum bactericidal activity. FACS confirmed its cell surface location.
Growth of E. coli expressing the 919LOrf4 protein at 37° C. resulted in lysis of the bacteria. In order to overcome this problem, the recombinant bacteria were grown at 30° C. Lysis was prevented without preventing expression.
It was hypothesised that proteins 907, 919 and 922 are murein hydrolases, and more particularly lytic transglycosylases. Murein hydrolases are located on the outer membrane and participate in the degradation of peptidoglycan.
The purified proteins 919untagged, 919Lorf4, 919-His (i.e. with a C-terminus His-tag) and 922-His were thus tested for murein hydrolase activity [Ursinus & Holtje (1994) J. Bact. 176:338-343]. Two different assays were used, one determining the degradation of insoluble murein sacculus into soluble muropeptides and the other measuring breakdown of poly(MurNAc-GlcNAc)n>30 glycan strands.
The first assay uses murein sacculi radiolabelled with meso-2,6-diamino-3,4,5-[3H]pimelic acid as substrate. Enzyme (3-10 μg total) was incubated for 45 minutes at 37° C. in a total volume of 100 μl comprising 10 mM Tris-maleate (pH 5.5), 10 mM MgCl2, 0.2% v/v Triton X-100 and [3H]A2 pm labelled murein sacculi (about 10000 cpm). The assay mixture was placed on ice for 15 minutes with 100 μl of 1% w/v N-acetyl-N,N,N-trimethylammonium for 15 minutes and precipitated material pelleted by centrifugation at 10000 g for 15 minutes. The radioactivity in the supernatant was measured by liquid scintillation counting. E. coli soluble lytic transglycosylase Slt70 was used as a positive control for the assay; the negative control comprised the above assay solution without enzyme.
All proteins except 919-His gave positive results in the first assay.
The second assay monitors the hydrolysis of poly(MurNAc-GlcNAc)glycan strands. Purified strands, poly(MurNAc-GlcNAc)n>30 labelled with N-acetyl-D-1-[3H]glucosamine were incubated with 3 μg of 919L in 10 mM Tris-maleate (pH 5.5), 10 mM MgCl2 and 0.2% v/v Triton X-100 for 30 min at 37° C. The reaction was stopped by boiling for 5 minutes and the pH of the sample adjusted to about 3.5 by addition of 10 μl of 20% v/v phosphoric acid. Substrate and product were separated by reversed phase HPLC on a Nucleosil 300 C18 column as described by Harz et. al. [Anal. Biochem. (1990) 190:120-128]. The E. coli lytic transglycosylase Mlt A was used as a positive control in the assay. The negative control was performed in the absence of enzyme.
By this assay, the ability of 919LOrf4 to hydrolyse isolated glycan strands was demonstrated when anhydrodisaccharide subunits were separated from the oligosaccharide by HPLC.
Protein 919Lorf4 was chosen for kinetic analyses. The activity of 919Lorf4 was enhanced 3.7-fold by the addition of 0.2% v/v Triton X-100 in the assay buffer. The presence of Triton X-100 had no effect on the activity of 919. The effect of pH on enzyme activity was determined in Tris-Maleate buffer over a range of 5.0 to 8.0. The optimal pH for the reaction was determined to be 5.5, Over the temperature range 18° C. to 42° C., maximum activity was observed at 37° C. The effect of various ions on murein hydrolase activity was determined by performing the reaction in the presence of a variety of ions at a final concentration of 10 mM, Maximum activity was found with Mg2+, which stimulated activity 2.1-fold. Mn2+ and Ca2+ also stimulated enzyme activity to a similar extent while the addition Ni2+ and EDTA had no significant effect. In contrast, both Fe2+ and Zn2+ significantly inhibited enzyme activity. The structures of the reaction products resulting from the digestion of unlabelled E. coli murein sacculus were analysed by reversed-phase HPLC as described by Glauner [Anal. Biochem. (1988) 172:451-464]. Murein sacculi digested with the muramidase Cellosyl were used to calibrate and standardise the Hypersil ODS column. The major reaction products were 1,6 anhydrodisaccharide tetra and tri peptides, demonstrating the formation of 1,6 anhydronmraminic acid intramolecular bond.
These results demonstrate experimentally that 919 is a murein hydrolase and in particular a member of the lytic transglycosylase family of enzymes. Furthermore the ability of 922-His to hydrolyse murein sacculi suggests this protein is also a lytic transglycosylase.
This activity may help to explain the toxic effects of 919 when expressed in E. coli.
In order to eliminate the enzymatic activity, rational mutagenesis was used, 907, 919 and 922 show fairly low homology to three membrane-bound lipidated murein lytic transglycosylases from Exalt:
907-2 also shares homology with E. coli MLTD (P23931) and Slt70 (P03810), a soluble lytic transglycosylase that is located in the periplasmic space. No significant sequence homology can be detected among 919, 922 and 907-2, and the same is true among the corresponding MLTA, MLTB and MLTC proteins.
Crystal structures are available for Slt70 [1QTEA; 1QTEB; Thunnissen et al. (1995) Biochemistry 34:12729-12737] and for Slt35 [1LTM; 1QUS; 1QUT; van, Asselt et at (1999) Structure Fold Des 7:1167-80] which is a soluble form of the 40 kDa MLTB.
The catalytic residue (a glutamic acid) has been identified for both Slt70 and MLTB.
In the case of Slt70, mutagenesis studies have demonstrated that even a conservative substitution of the catalytic Glu505 with a glutamine (Gln) causes the complete loss of enzymatic activity. Although Slt35 has no obvious sequence similarity to Slt70, their catalytic domains shows a surprising similarity. The corresponding catalytic residue in MLTB is Glu162.
Another residue which is believed to play an important role in the correct folding of the enzymatic cleft, is a well-conserved glycine (Gly) downstream of the glutamic acid. Recently, Terrak et al. [Mol. Microbiol. (1999) 34:350-64] have suggested the presence of another important residue which is an aromatic amino acid located around 70-75 residues downstream of the catalytic glutamic acid.
Sequence alignment of Slt70 with 907-2 and of MLTB with 922 were performed in order to identify the corresponding catalytic residues in the MenB antigens.
The two alignments in the region of the catalytic domain are reported below:
From these alignments, it results that the corresponding catalytic glutamate in 907-2 is Glu117, whereas in 922 is Glu164. Both antigens also share downstream glycines that could have a structural role in the folding of the enzymatic cleft (in bold), and 922 has a conserved aromatic residue around 70aa downstream (in bold).
In the case of protein 919, no 3D structure is available for its E. coli homologue MLTA, and nothing is known about a possible catalytic residue. Nevertheless, three amino acids in 919 are predicted as catalytic residues by alignment with MLTA:
270
280 290
340 ⋄350 ⋄
The three possible catalytic residues are shown by the symbol ▾:
Alignments of polymorphic forms of 919 are disclosed in WO00/66741.
Based on the prediction of catalytic residues, three mutants of the 919 and one mutant of 907, containing each a single Amino acid substitution, have been generated. The glutamic acids in position 255 and 323 and the aspartic acids in position 362 of the 919 protein and the glutamic acid in position 117 of the 907 protein, were replaced with glycine residues using PCR-based SDM. To do this, internal primers containing a codon change from Glu or Asp to Gly were designed:
To generate the 919-E255, 919-E323 and 919-E362 mutants, PCR was performed using 20 ng of the pET 919-LOrf4 DNA as template, and the following primer pairs:
The second round of PCR was performed using the product of PCR 1-2, 3-4 or 5-6 as template, and as forward and reverse primers the “Orf4L for” and “919L rev” respectively.
For the mutant 907-E117, PCR have been performed using 200 ng of chromosomal DNA of the 2996 strain as template and the following primer pairs:
The second round of PCR was performed using the products of PCR 7 and 8 as templates and the oligos “907L for” and “907L rev” as primers.
The PCR fragments containing each mutation were processed following the standard procedure, digested with NdeI and XhoI restriction enzymes and cloned into pET-21b+ vector. The presence of each mutation was confirmed by sequence analysis.
Mutation of Glu117 to Gly in 907 is carried out similarly, as is mutation of residues Glu164, Ser213 and Asn348 in 922.
The E255G mutant of 919 shows a 50% reduction in activity; the E3230 mutant shows a 70% reduction in activity; the E362G mutant shows no reduction in activity.
287-GST, 919untagged and 953-His were subjected to gel filtration for analysis of quaternary structure or preparative purposes. The molecular weight of the native proteins was estimated using either FPLC Superose 12 (H/R 10/30) or Superdex 75 gel filtration columns (Pharmacia). The buffers used for chromatography for 287, 919 and 953 were 50 mM Tris-HO (pH 8.0), 20 mM Bicine (pH 8.5) and 50 mM Bicine (pH 8.0), respectively.
Additionally each buffer contained 150-200 mM NaCl and 10% v/v glycerol. Proteins were dialysed against the appropriate buffer and applied in a volume of 204.1. Gel filtration was performed with a flow rate of 0.5-2.0 ml/min and the eluate monitored at 280 nm. Fractions were collected and analysed by SDS-PAGE. Blue dextran 2000 and the molecular weight standards ribonuclease A, chymotrypsin A ovalbumin, albumin (Pharmacia) were used to calibrate the column. The molecular weight of the sample was estimated from a calibration curve of Kav log Mr of the standards. Before gel filtration, 287-GST was digested with thrombin to cleave the GST moiety.
The estimated molecular weights for 287, 919 and 953-His were 73 kDa, 47 kDa and 43 kDa respectively. These results suggest 919 is monomeric while both 287 and 953 are principally dimeric in their nature. In the case of 953-His, two peaks were observed during gel filtration. The major peak (80%) represented a dimeric conformation of 953 while the minor peak (20%) had the expected size of a monomer. The monomeric form of 953 was found to have greater bactericidal activity than the dimer.
953 protein with its native leader peptide and no fusion partners was expressed from the pET vector and also from pSM214 [Velati Bellini et al. (1991) J. Biotechnol. 18, 177-192].
The 953 sequence was cloned as a full-length gene into pSM214 using the E. coli MM1294-1 strain as a host. To do this, the entire DNA sequence of the 953 gene (from ATG to the STOP codon) was amplified by PCR using the following primers:
which contain EcoRI and HindIII restriction sites, respectively. The amplified fragment was digested with EcoRI and HindIII and ligated with the pSM214 vector digested with the same two enzymes. The ligated plasmid was transformed into E. coli MM294-1 cells (by incubation in ice for 65 minutes at 37° C.) and bacterial cells plated on LB agar containing 20 μg/ml of chloramphenicol.
Recombinant colonies were grown over-night at 37° C. in 4 ml of LB broth containing 20 μg/ml of chloramphenicol; bacterial cells were centrifuged and plasmid DNA extracted as and analysed by restriction with EcoRI and HindIII. To analyse the ability of the recombinant colonies to express the protein, they were inoculated in LB broth containing 20 μg/ml of chloramphenicol and let to grown for 16 hours at 37° C. Bacterial cells were centrifuged and resuspended in PBS. Expression of the protein was analysed by SDS-PAGE and Coomassie Blue staining.
Expression levels were unexpectedly high from the pSM214 plasmid.
Oligos used to clone sequences into pSM-214 vectors were as follows:
These sequences were manipulated, cloned and expressed as described for 953L.
For the pET-24 vector, sequences were cloned and the proteins expressed in pET-24 as described below for pET21. pET2 has the same sequence as pET-21, but with the kanamycin resistance cassette instead of ampicillin cassette.
Oligonucleotides used to clone sequences into pET-24b vector were:
ORF1 from N. meningitidis (serogroup B, strain MC58) is predicted to be an outer membrane or secreted protein. It has the following sequence:
MKTTDKRTTE THRKAPKTGR IRFSPAYLAI CLSFGILPQA WAGHTYFGIN
The leader peptide is underlined.
A polymorphic form of ORF1 is disclosed in WO99/55873.
Three expression strategies have been used for ORF1:
MKKTAIAIAVALAGFATVAQAASAGHTYFGINYQYYRDFAENKGKFAVGA
All three forms of the protein were expressed. The His-tagged protein could be purified and was confirmed as surface exposed, and possibly secreted (see
ORF1LOmpA was purified as total membranes, and was localised in both the inner and outer membranes. Unexpectedly, sera raised against. ORF1LOmpA show even better ELISA and anti-bactericidal properties than those raised against the His-tagged protein.
ORF1L was purified as outer membranes, where it is localised.
Protein 911 from N. meningitidis (serogroup B, strain MC58) has the following sequence:
MKKNILEFWV GLFVLIGAAA VAFLAFRVAG GAAFGGSDKT
The leader peptide is underlined.
Three expression strategies have been used for 911:
All three forms of the protein were expressed. ELISA titres were highest using 911L, with 919LOmpA also giving good results.
The complete ORF46 protein from N. meningitidis (serogroup B, strain 2996) has the following sequence:
LGISRKISLI LSILAVCLPM HAHASDLAND SFIRQVLDRQ
The leader peptide is underlined.
The sequences of ORF46 from other strains can be found in WO00/66741.
Three expression strategies have been used for ORF46:
ORF46-2L is expressed at a very low level to E. coli. Removal of its leader peptide (ORF46-2) does not solve this problem. The truncated ORF46.1L form (first 423 amino acids, which are well conserved between serogroups and species), however, is well-expressed and gives excellent results in ELISA test and in the bactericidal assay.
ORF46.1 has also been used as the basis of hybrid proteins. It has been fused with 287, 919, and ORF1. The hybrid proteins were generally insoluble, but gave some good ELISA and bactericidal results (against the homologous 2996 strain):
For comparison, ‘triple’ hybrids of ORF46.1, 287 (either as a GST fusion, or in ΔG287 form) and 919 were constructed and tested against various strains (including the homologous 2996 strain) versus a simple mixture of the three antigens. FCA was used as adjuvant
Again, the hybrids show equivalent or superior immunological activity.
Hybrids of two proteins (strain 2996) were compared to the individual proteins against various heterologous strains:
Again, the hybrid shows equivalent or superior immunological activity.
The complete 961 protein from N. meningitidis (serogroup B, strain MC58) has the following sequence:
MSMKHFPAKV LTTAILATFC SGALAATSDD DVKKAATVAI
The leader peptide is underlined.
Three approaches to 961 expression were used:
All three forms of the protein were expressed. The GST-fusion protein could be purified and antibodies against it confirmed that 961 is surface exposed (
Protein 961 appears to be phase variable. Furthermore, it is not found in all strains of N. meningitidis.
Protein 287 from N. meningitidis (serogroup B, strain 2996) has the following sequence;
MFERSVIAMA CIFALSACGG GGGGSPDVKS ADTLSKPAAP
The leader peptide is shown underlined.
The sequences of 287 from other strains can be found in FIGS. 5 and 15 of WO00/66741.
Example 9 of WO99/57280 discloses the expression of 287 as a GST-fusion in E. coli.
A number of further approaches to expressing 287 in E. coli have been used, including:
All these proteins could be expressed and purified.
‘287L’ and ‘287 LOrf4’ were confirmed as lipoproteins.
As shown in
A similar approach was adopted for E. coli expression of further proteins from WO99/24578, WO99/36544 and WO99/57280.
The following were expressed without a fusion partner: 008, 105, 117-1, 121-1, 122-1, 128-1, 148, 216, 243, 308, 593, 652, 726, 982, and Orf143-1. Protein 117-1 was confirmed as surface-exposed by FACS and gave high ELISA titres.
The following were expressed with the native leader peptide but without a fusion partner: 111, 149, 206, 225-1, 235, 247-1, 274, 283, 286, 292, 401, 406, 502-1, 503, 519-1, 525-1, 552, 556, 557, 570, 576-1, 580, 583, 664, 759, 907, 913, 920-1, 926, 936-1, 953, 961, 983, 989, Orf4, Orf7-1, Orf9-1, Orf23, Orf25, Orf37, Orf38, Orf40, Orf40.1, Orf40.2, Orf72-1, Orf76-1, Orf85-2, OrF91, Orf97-1, Orf119, Orf143.1. These proteins are given the suffix ‘L’.
His-tagged protein 760 was expressed with and without its leader peptide. The deletion of the signal peptide greatly increased expression levels. The protein could be purified most easily using 2M urea for solubilisation.
His-tagged protein 264 was well-expressed using its own signal peptide, and the 30 kDa protein gave positive Western blot results.
All proteins were successfully expressed.
The localisation of 593, 121-1, 128-1, 593, 726, and 982 in the cytoplasm was confirmed.
The localisation of 920-1L, 953L, ORF9-1L, ORF85-2L, ORF97-1L, 570L, 580L and 664L in the periplasm was confirmed.
The localisation of ORF40L in the outer membrane, and 008 and 519-1L in the inner membrane was confirmed. ORF25L, ORF4L, 406L, 576-1L were all confirmed as being localised in the membrane.
Protein 206 was found not to be a lipoprotein.
ORF25 and ORF40 expressed with their native leader peptides but without fusion partners, and protein 593 expressed without its native leader peptide and without a fusion partner, raised good anti-bactericidal sera. Surprisingly, the forms of ORF25 and ORF40 expressed without fusion partners and using their own leader peptides (i.e. ‘ORF25L’ and ‘ORF40L’) give better results in the bactericidal assay than the fusion proteins.
Proteins 920L and 953L were subjected to N-terminal sequencing, giving
The N-terminal sequence of protein 519.1L localised in the inner membrane was
The incorporation of palmitate in recombinant lipoproteins was demonstrated by the method of Kraft et. al. [J. Bact. (1998) 180:3441-3447.]. Single colonies harbouring the plasmid of interest were grown overnight at 37° C. in 20 ml of LB/Amp (100 μg/ml) liquid culture. The culture was diluted to an OD550 of 0.1 in 5.0 ml of fresh medium LB/Amp medium containing 5 μC/ml [3H] palmitate (Amersham). When the OD550 of the culture reached 0.4-0.8, recombinant lipoprotein was induced for 1 hour with IPTG (final concentration 1.0 mM). Bacteria were harvested by centrifugation in a bench top centrifuge at 2700 g for 15 min and washed twice with 1.0 ml cold PBS. Cells were resuspended in 120 μl of 20 mM Tris-HCl (pH 8.0), 1 mM EDTA, 1.0% w/v SDS and lysed by boiling for 10 min. After centrifugation at 13000 g for 10 min the supernatant was collected and proteins precipitated by the addition of 1.2 ml cold acetone and left for 1 hour at −20° C. Protein was pelleted by centrifugation at 13000 g for 10 min and resuspended in 20-50 μl (calculated to standardise loading with respect to the final 0.1) of the culture) of 1.0% w/v SDS. An aliquot of 15 μl was boiled with 5 μl of SDS-PAGE sample buffer and analysed by SDS-PAGE. After electrophoresis gels were fixed for 1 hour in 10% v/v acetic acid and soaked for 30 minutes in Amplify solution (Amersham). The gel was vacuum-dried under heat and exposed to Hyperfilm (Kodak) overnight −80° C.
Incorporation of the [3H] palmitate label, confirming lipidation, was found for the following proteins: Orf4L, Orf25L, 287L, 287LOrf4, 406.L, 576L, 926L, 919L and 9191, Orf4.
Based on homology of different regions of 287 to proteins that belong to different functional classes, it was split into three ‘domains’, as shown in
Each of the three ‘domains’ shows a different degree of sequence conservation between N. meningitidis strains domain C is 98% identical, domain A is 83% identical, whilst domain B is only 71% identical. Note that protein 287 in strain MC58 is 61 amino acids longer than that of strain 2996. An alignment of the two sequences is shown in
The three domains were expressed individually as C-terminal His-tagged proteins. This was done for the MC58 and 2996 strains, using the following constructs:
To make these constructs, the stop codon sequence was omitted in the 3′-end primer sequence. The 5′ primers included the NheI restriction site, and the 3′ primers included a Kiwi as a tail, in order to direct the cloning of each amplified fragment into the expression vector pRT21b4 rising NdeI-XhoI, NheI-XhoI or NdeI-HindIII restriction sites.
All six constructs could be expressed, but 287b-MC8 required denaturation and refolding for solubilisation.
Deletion of domain A is described below (‘Δ4 287-His’).
Immunological data (serum bactericidal assay) were also obtained using the various domains from strain 2996, against the homologous and heterologous MenB strains, as well as MenA (F6124 strain) and MenC (BZ133 strain):
Using the domains of strain MC58, the following results were obtained:
As well as expressing individual domains, 287 was also expressed (as a C-terminal His-tagged protein) by making progressive deletions within the first domain. These Four deletion mutants of protein 287 from strain 2996 were used (
The ‘Δ4’ protein was also made for strain MC58 (‘Δ4 287MC58-His’; an 203-488).
The constructs were made in the same way as 287a/b/c, as described above.
All six constructs could be expressed and protein could be purified. Expression of 287-His was, however, quite poor.
Expression was also high when the C-terminal His-tags were omitted.
Immunological data (serum bactericidal assay) were also obtained using the deletion mutants, against the homologous (2996) and heterologous MenB strains, as well as MenA (F6124 strain) and MenC (BZ133 strain):
The same high activity for the Δ4 deletion was seen using the sequence from strain MC58.
As well as showing superior expression characteristics, therefore, the mutants are immunologically equivalent or superior.
The ‘Δ1 287-His’ construct of the previous example differs from 287-His and from ‘287untagged’ only by a short N-terminal deletion (GGGGGGS). Using an expression vector which replaces the deleted serine with a codon present in the Nhe cloning site, however, this amounts to a deletion only of (Gly)6. Thus, the deletion of this (Gly)6 sequence has been shown to have a dramatic effect on protein expression.
The protein lacking the N-terminal amino acids up to GGGGGG is called ‘ΔG287’. In strain MC58, its sequence (leader peptide underlined) is:
ΔG287
MFKRSVIAMA CIFALSACGG GGGGSPDVKS ADTLSKPAAP
ΔG287, with or without His-tag (‘ΔG287-His’ and ‘ΔG287K’, respectively), are expressed at very good levels in comparison with the ‘287-His’ or ‘287untagged’.
On the basis of gene variability data, variants of ΔG287-His were expressed in E. coli from a number of MenB strains, in particular from strains 2996, MC58, 1000, and BZ232. The results were also good.
It was hypothesised that poly-Gly deletion might be a general strategy to improve expression. Other MenB lipoproteins containing similar (Gly)n motifs (near the N-terminus, downstream of a cysteine) were therefore identified, namely Tbp2 (N/v1130460), 741 (NMB 1870) and 983 (NMB1969):
ΔGTbp2
MNNPLVNQAA MVLPVFLLSA CLGGGGSFDL DSVDTEAPRP APKYQDVFSE
ΔG741
VNRTAFCCLS LTTALILTAC SSGGGGVAAD IGAGLADALT APLDHKDKGL
ΔG983
MRTTPTFPTK TFKPTAMALA VATTLSACLG GGGGGTSAPD FNAGGTGIGS
Thp2 and 741 genes were from strain MC58; 983 and 287 genes were from strain 2996. These were cloned in pET vector and expressed in E. coli without the sequence coding for their leader peptides or as “ΔG forms”, both fused to a C-terminal His-tag. In each case, the same effect was seen expression was good in the clones carrying the deletion of the poly-glycine stretch, and poor or absent if the glycines were present in the expressed protein:
SDS-PAGE of the proteins is shown in
ΔG287 and Hybrids
ΔG287 proteins were made and purified for strains MC58, 1000 and BZ232. Each of these gave high ELISA titres and also serum bactericidal titres of >8192. ΔG287K, expressed from pET-24b, gave excellent titres in ELISA and the serum bactericidal assay. ΔG287-ORF46.1K may also be expressed in pET-24b.
ΔG287 was also fused directly in-frame upstream of 919, 953, 961 (sequences shown below) and ORF46.1:
The bactericidal efficacy (homologous strain) of antibodies raised against the hybrid proteins was compared with antibodies raised against simple mixtures of the component antigens (using 287-GST) for 919 and ORF46.1:
Data for bactericidal activity against heterologous MenB strains and against serotypes A and C were also obtained:
The hybrid proteins with ΔG287 at the N-terminus are therefore immunologically superior to simple mixtures, with ΔG287-ORF46.1 being particularly effective, even against heterologous strains: ΔG287-ORF46.1K may be expressed in pET-24b.
The same hybrid proteins were made using New Zealand strain 394198 rather than 2996:
Bactericidal titres generated in response to ΔG983 (His-fusion) were measured against various strains, including the homologous 2996 strain:
ΔG983 was also expressed as a hybrid, with ORF46.1, 741, 961 or 961c at its C-terminus:
Bactericidal litres generated in response to ΔG741 (His-fusion) were measured against various strains, including the homologous 2996 strain:
As can be seen, the ΔG741-induced anti-bactericidal titre is particularly high against heterologous strain MC58.
ΔG741 was also fused directly in-frame upstream of proteins 961, 961c, 983 and ORF46.1:
According to the invention, hybrids of two proteins A & B may be either NH2-A-B-COOH or NH2-B-A-COOH. The effect of this difference was investigated using protein 287 either C-terminal (in ‘287-His’ form) or N-terminal (in ΔG287 form sequences shown above) to 919, 953 and ORF46.1. A panel of strains was used, including homologous strain 2996. FCA was used as adjuvant:
Better bactericidal titres are generally seen with 287 at the N-terminus m the ΔG form)
When fused to protein 961 [NH2-ΔG287-961-COOH sequence shown above], the resulting protein is insoluble and must be denatured and renatured for purification. Following renaturation, around 50% of the protein was found to remain insoluble. The soluble and insoluble proteins were compared, and much better bactericidal titres were obtained with the soluble protein (FCA as adjuvant):
Titres with the insoluble form were, however, improved by using alum adjuvant instead:
Expression of protein 287 as full-length with a C-terminal His-tag, or without its leader peptide but with a C-terminal His-tag, gives fairly low expression levels. Better expression is achieved using a N-terminal GST-fusion.
As an alternative to using GST as an N-terminal fusion partner, 287 was placed at the C-terminus of protein 919 (‘919-287’), of protein 953 (‘953-287’), and of proteins ORF46.1 (‘ORF46.1-287’). In both cases, the leader peptides were deleted, and the hybrids were direct in-frame fusions.
To generate the 953-287 hybrid, the leader peptides of the two proteins were omitted by designing the forward primer downstream from the leader of each sequence; the stop codon sequence was omitted in the 953 reverse primer but included in the 287 reverse primer. For the 953 gene, the 5′ and the 3′ primers used for amplification included a NdeI and a BamHI restriction sites respectively, whereas for the amplification of the 287 gene the 5′ and the 3′ primers included a BamHI and a XhoI restriction sites respectively. In this way a sequential directional cloning of the two genes in pET21b+, using NdeI-BamHI (to clone the first gene) and subsequently BamHI-XhoI (to clone the second gene) could be achieved.
The 919-287 hybrid was obtained by cloning the sequence coding for the mature portion of 287 into the XhoI site at the 3′-end of the 919-His clone in pET21b+. The primers used for amplification of the 287 gene were designed for introducing a SalI restriction site at the 5′- and a XhoI site at the 3′- of the PCR fragment. Since the cohesive ends produced by the SalI and XhoI restriction enzymes are compatible, the 287 PCR product digested with SalI-XhoI could be inserted in the pET21b-919 clone cleaved with XhoI.
The ORF46.1-287 hybrid was obtained similarly.
The bactericidal efficacy (homologous strain) of antibodies raised against the hybrid proteins was compared with antibodies raised against simple mixtures of the component antigens:
Data for bactericidal activity against heterologous MenB strains and against serotypes A and C were also obtained for 919-287 and 953-287:
Hybrids of ORF46.1 and 919 were also constructed. Best results (four-fold higher titre) were achieved with 919 at the N-terminus.
Hybrids 919-519His, ORF97-225His and 225-ORF97His were also tested. These gave moderate ELISA fitres and bactericidal antibody responses.
As shown above, the leader peptide of ORF4 can be fused to the mature sequence of other proteins (e.g. proteins 287 and 919). It is able to direct lipidation in E. coli.
The protein ‘564’ is very large (2073aa), and it is difficult to clone and express it in complete form. To facilitate expression, the protein has been divided into four domains, as shown in
These domains show the following homologies:
Using the MC58 strain sequence, good intracellular expression of 564ab was obtained in the form of GST-fusions (no purification) and his-tagged protein; this domain-pair was also expressed as a lipoprotein, which showed moderate expression in the outer membrane/supernatant fraction.
The b domain showed, moderate intracellular expression when expressed as a his-tagged product (no purification), and good expression as a GST-fusion.
The c domain showed good intracellular expression as a GST-fusion, but was insoluble. The d domain showed moderate intracellular expression as a his-tagged product (no purification). The cd protein domain-pair showed moderate intracellular expression (no purification) as a GST-fusion,
Good bactericidal assay titres were observed using the c domain and the be pair.
The 20mer leader peptide from 919 is discussed in example 1 above:
As shown in example 1, deletion of this leader improves heterologous expression, as does substitution with the ORF4 leader peptide. The influence of the 919 leader on expression was investigated by fusing the coding sequence to the PhoC reporter gene from Morganella morganii [Thaller et al. (1994) Microbiology 140:1341-1350]. The construct was cloned in the pET21-b plasmid between the NdeI and XhoI sites (
MKKYLFRAAL YGIAAAILAA AIPAGNDATT KPDLYYLKNE QAIDSLKLLP
The level of expression of PhoC from this plasmid is >200-fold lower than that found for the same construct but containing the native PhoC signal peptide. The same result was obtained even after substitution of the T7 promoter with the E. coli Plac promoter. This means that the influence of the 919 leader sequence on expression does not depend on the promoter used.
In order to investigate if the results observed were due to some peculiarity of the 919 signal peptide nucleotide sequence (secondary structure formation, sensitivity to RNAases, etc.) or to protein instability induced by the presence of this signal peptide, a number of mutants were generated. The approach used was a substitution of nucleotides of the 919 signal peptide sequence by cloning synthetic linkers containing degenerate codons. In this way, mutants were obtained with nucleotide and/or amino acid substitutions.
Two different linkers were used, designed to produce mutations in two different regions of the 919 signal peptide sequence, in the first 19 base pairs (L1) and between bases 20-36 (S1).
The alignment of some of the mutants obtained is given below.
As shown in the sequences alignments, most of the mutants analysed contain in-frame deletions which were unexpectedly produced by the host cells.
Selection of the mutants was performed by transforming E. coli BL21(DE3) cells with DNA prepared from a mixture of L1 and S1 mutated clones. Single transformants were screened for high PhoC activity by streaking them onto LB plates containing 100 μg/ml ampicillin, 50 μg/ml methyl green, 1 mg/ml PDP (phenolphthaleindiphosphate). On this medium PhoC-producing cells become green (
A quantitative analysis of PhoC produced by these mutants was carried out in liquid medium using pNPP as a substrate for PhoC activity. The specific activities measured in cell extracts and supernatants of mutants grown in liquid medium for 0, 30, 90, 180 min. were:
Some of the mutants produce high amounts of PhoC and in particular, mutant 9L1a can secrete PhoC in the culture medium. This is noteworthy since the signal peptide sequence of this mutant is only 9 amino acids long. This is the shortest signal peptide described to date.
MafB-related proteins include 730, ORF46 and ORF29.
The 730 protein from MC58 has the following sequence:
VKPLRRLTNL LAACAVAAAA LIQPALAADL AQDPFITDNA QRQHYEPGGK
The leader peptide is underlined.
730 shows similar features to ORF46 (see example 8 above):
To overcome this toxicity, a similar approach was used for 730 as described in example 8 for ORF46. Four C-terminal truncated forms were obtained, each of which is well expressed. All were obtained from intracellular expression of His-tagged leaderless 730.
Form A consists of the N-terminal hydrophilic region of the mature protein (aa. 28-226). This was purified as a soluble His-tagged product, having a higher-than-expected MW.
Form B extends to the end of the region conserved between serogroups (aa. 28-340). This was purified as an insoluble His-tagged product.
The C-terminal truncated forms named C1 and C2 were obtained after screening for clones expressing high levels of 730-His clones in strain HMS174(DE3). Briefly, the pET21b plasmid containing the His-tagged sequence coding for the full-length mature 730 protein was used to transform the recA strain HMS174(DE3). Transformants were obtained at low frequency which showed two phenotypes: large colonies and very small colonies. Several large and small colonies were analysed for expression of the 730-His clone. Only cells from large colonies over-expressed a protein recognised by anti-730A antibodies. However the protein over-expressed in different clones showed differences in molecular mass. Sequencing of two of the clones revealed that in both cases integration of an E. coli IS sequence had occurred within the sequence coding for the C terminal region of 730. The two integration events have produced in-frame fusion with 1 additional codon in the case of C1, and 12 additional codons in the case of C2 (
The additional amino acid produced by the insertion is underlined.
LLG*
The additional amino acids produced by the insertion are underlined.
In conclusion, intracellular expression of the 730-C1 form gives very high level of protein and has no toxic effect on the host cells, whereas the presence of the native C-terminus is toxic. These data suggest that the “intracellular toxicity” of 730 is associated with the C-terminal 65 amino acids of the protein.
Equivalent truncation of ORF29 to the first 231 or 368 amino acids has been performed, using expression with or without the leader peptide (amino acids 1-26; deletion gives cytoplasmic expression) and with or without a His-tag.
As described in example 9 above, the OST-fusion of 961 was the best-expressed in Exoli. To improve expression, the protein was divided into domains (
The domains of 961 were designed on the basis of YadA (an adhesin produced by Yersinia which has been demonstrated to be an adhesin localized on the bacterial surface that forms oligomers that generate surface projection [Hoiczyk et al. (2000) EMBO J 19:5989-99]) and are: leader peptide, head domain, coiled-coil region (stalk), and membrane anchor domain.
These domains were expressed with or without the leader peptide, and optionally fused either to C-terminal His-tag or to N-terminal GST. Exalt: clones expressing different domains of 961 were analyzed by SDS-PAGE and western blot for the production and localization of the expressed protein, from over-night (o/n) culture or after 3 hours induction with IPTG. The results were:
The results show that in E. coli:
Titres in ELISA and in the serum bactericidal assay using His-fusions were as follows:
E. coli clones expressing different forms of 961 (961, 961-L, 961Δ1-L and 961c-L) were used to investigate if the 961 is an adhesin (c.f. YadA). An adhesion assay was performed using (a) the human epithelial cells and (b) E. coli clones after either over-night culture or three hours IPTG induction. 961-L grown over-night (961Δ1-L) and IPTG-induced 961c-L (the clones expressing protein on surface) adhere to human epithelial cells.
961c was also used in hybrid proteins (see above). As 961 and its domain variants direct efficient expression, they are ideally suited as the N-terminal portion of a hybrid protein.
Further hybrid proteins of the invention are shown below (see also
It will be understood that the invention has been described by way of example only and modifications may be made whilst remaining within the scope and spirit of the invention. For instance, the use of proteins from other strains is envisaged [e.g. see WO00/66741 for polymorphic sequences for ORF4, ORF40, ORF46, 225, 235, 287, 519, 726, 919 and 953].
The following table summarises the FPLC protein purification that was used:
Buffer solutions included 20-120 mM NaCl, 5.0 mg/ml CHAPS and 10% v/v glycerol. The dialysate was centrifuged at 13000 g for 20 min and applied to either a mono Q or mono S FPLC ion-exchange resin. Buffer and ion exchange resins were chosen according to the pI of the protein of interest and the recommendations of the FPLC protocol manual [Pharmacia: FPLC Ion Exchange and Chromatofocussing; Principles and Methods. Pharmacia Publication]. Proteins were eluted using a step-wise NaCl gradient. Purification was analysed by SDS-PAGE and protein concentration determined by the Bradford method.
The letter in the ‘protocol’ column refers to the following:
FPLC-A:
Clones 121.1, 128.1, 593, 726, 982, periplasmic protein 920L and hybrid proteins 919-287, 953-287 were purified from the soluble fraction of E. coli obtained after disruption of the cells. Single colonies harbouring the plasmid of interest were grown overnight at 37° C. in 20 ml of LB/Amp (100 μg/ml) liquid culture. Bacteria were diluted 1:30 in 1.0 L of fresh medium and grown at either 30° C. or 37° C. until the OD550 reached 0.6-08. Expression of recombinant protein was induced with/PTO at a final concentration of 1.0 mM. After incubation for 3 hours, bacteria were harvested by centrifugation at 8000 g for 15 minutes at 4° C. When necessary cells were stored at −20° C. All subsequent procedures were performed on ice or at 4° C. For cytosolic proteins (121.1, 128.1, 593, 726 and 982) and periplasmic protein 920L, bacteria were resuspended in 25 ml of PBS containing complete protease inhibitor (Boehringer-Mannheim). Cells were lysed by by sonication using a Branson Sonifier 450. Disrupted cells were centrifuged at 8000 g for 30 min to sediment unbroken cells and inclusion bodies and the supernatant taken to 35% v/v saturation by the addition of 3.9 M (NH4)2SO4. The precipitate was sedimented at 8000 g for 30 minutes. The supernatant was taken to 70% v/v saturation by the addition of 3.9 M (NH4)2SO4 and the precipitate collected as above. Pellets containing the protein of interest were identified by SDS-PAGE and dialysed against the appropriate ion-exchange buffer (see below) for 6 hours or overnight. The periplasmic fraction from E. coli expressing 953L was prepared according to the protocol of Evans et. al. [Infect. Immun. (1974) 10:1010-1017] and dialysed against the appropriate ion-exchange buffer. Buffer and ion exchange resin were chosen according to the pI of the protein of interest and the recommendations of the FPLC protocol manual (Pharmacia). Buffer solutions included 20 mM NaCl, and 10% (v/v) glycerol. The dialysate was centrifuged at 13000 g for 20 min and applied to either a mono Q or mono S FPLC ion-exchange resin. Buffer and ion exchange resin were chosen according to the pI of the protein of interest and the recommendations of the FPLC protocol manual (Pharmacia). Proteins were eluted from the ion-exchange resin using either step-wise or continuous NaCl gradients. Purification was analysed by SDS-PAGE and protein concentration determined by Bradford method. Cleavage of the leader peptide of periplasmic proteins was demonstrated by sequencing the NH2-terminus (see below).
FPLC-B:
These proteins were purified from the membrane fraction of E. coli, Single colonies harbouring the plasmid of interest were grown overnight at 37° C. in 20 ml of LB/Amp (100 μg/ml) liquid culture. Bacteria were diluted 1:30 in 1.0 L of fresh medium. Clones 406.1L and 919LOrf4 were grown at 30° C. and Orf25L and 576.1L at 37° C. until the OD550 reached 0.6-0.8. In the case of 919LOrf4, growth at 30° C. was essential since expression of recombinant protein at 37° C. resulted in lysis of the cells. Expression of recombinant protein was induced with IPTG at a final concentration of 1.0 mM. After incubation for 3 hours, bacteria were harvested by centrifugation at 8000 g for 15 minutes at 4° C. When necessary cells were stored at −20° C. AU subsequent procedures were performed at 4° C. Bacteria were resuspended in 25 ml of PBS containing complete protease inhibitor (Boehringer-Mannheim) and lysed by osmotic shock with 2-3 passages through a French Press. Unbroken cells were removed by centrifugation at 5000 g for 15 min and membranes precipitated by centrifugation at 100000 g (Beckman Ti50, 38000 rpm) for 45 minutes. A Dounce homogenizer was used to re-suspend the membrane pellet in 7.5 ml of 20 mM Tris-HCl (pH 8.0), 1.0 M NaCl and complete protease inhibitor. The suspension was mixed for 2-4 hours, centrifuged at 100000 g for 45 min and the pellet resuspended in 7.5 ml of 20 mM Tris-HCl (pH 8.0), 1.0M NaCl, 5.0 mg/ml CHAPS, 10% (v/v) glycerol and complete protease inhibitor. The solution was mixed overnight, centrifuged at 100000 g for 45 minutes and the supernatant dialysed for 6 hours against an appropriately selected buffer. In the case of Orf25L, the pellet obtained after CHAPS extraction was found to contain the recombinant protein. This fraction, without further purification, was used to immunise mice.
FPLC-C:
Identical to FPLC-A, but purification was from the soluble fraction obtained after permeabilising E. coli with polymyxin B, rather than after cell disruption.
FPLC-D:
A single colony harbouring the plasmid of interest was grown overnight at 37° C. in 20 ml of LB/Amp (100 μg/ml) liquid culture. Bacteria were diluted 1:30 in 1.0 L of fresh medium and grown at 30° C. until the OD550 reached 0.6-0.8. Expression of recombinant protein was induced with IPTG at a final concentration of 1.0 mM. After incubation for 3 hours, bacteria were harvested by centrifugation at 8000 g for 15 minutes at 4° C. When necessary cells were stored at −20° C. All subsequent procedures were performed on ice or at 4° C. Cells were resuspended in 20 mM Bicine (pH 8.5), 20 mM NaCl, 10% (v/v) glycerol, complete protease inhibitor (Boehringer-Mannheim) and disrupted using a Branson Sonifier 450. The sonicate was centrifuged at 8000 g for 30 rain to sediment unbroken cells and inclusion bodies. The recombinant protein was precipitated from solution between 35% v/v and 70% v/v saturation by the addition of 3.9M (NH4)2SO4. The precipitate was sedimented at 8000 g for 30 minutes, resuspended in 20 mM Bicine (pH 8.5), 20 mM NaCl, 10% (v/v) glycerol and dialysed against this buffer for 6 hours or overnight. The dialysate was centrifuged at 13000 g for 20 min and applied to the FPLC resin. The protein was eluted from the column using a step-wise NaCl gradients. Purification was analysed by SDS-PAGE and protein concentration determined by Bradford method.
Genes coding for antigens of interest were amplified by PCR, using oligonucleotides designed on the basis of the genomic sequence of N. meningitidis B MC58. Genomic DNA from strain 2996 was always used as a template in PCR reactions, unless otherwise specified, and the amplified fragments were cloned in the expression vector pET21b+(Novagen) to express the protein as C-terminal His-tagged product, or in pET-24b+(Novagen) to express the protein in ‘untagged’ form (e.g. AG 287K).
Where a protein was expressed without a fusion partner and with its own leader peptide (if present), amplification of the open reading frame (ATG to STOP codons) was performed.
Where a protein was expressed in ‘untagged’ form, the leader peptide was omitted by designing the 5′-end amplification primer downstream from the predicted leader sequence.
The melting temperature of the primers used in PCR depended on the number and type of hybridising nucleotides in the whole primer, and was determined using the formulae:
T
m1=4(G+C)+2(A+T) (tail excluded)
T
m2=64.9+0.41(% GC)−600/N (whole primer)
The melting temperatures of the selected oligonucleotides were usually 65-70° C. for the whole oligo and 50-60° C. for the hybridising region alone.
Oligonucleotides were synthesised using a Perkin Elmer 394 DNA/RNA Synthesizer, eluted from the columns in 2.0 ml NH4OH, and deprotected by 5 hours incubation at 56° C. The oligos were precipitated by addition of 0.3M Na-Acetate and 2 volumes ethanol. The samples were centrifuged and the pellets resuspended in water.
TAGC-GCTTTCCGCGTGGCCGGCGGTGC
§Forward primers used in combination with the 287-His Reverse primer.
In all constructs starting with an ATG not followed by a unique NheI site, the ATG codon is part of the NdeI site used for cloning. The constructs made using NheI as a cloning site at the 5° end (e.g. all those containing 287 at the N-terminus) have two additional codons (GCT AGC) fused to the coding sequence of the antigen.
Preparation of Chromosomal DNA Templates N. meningitidis strains 2996, MC58, 394.98, 1000 and BZ232 (and others) were grown to exponential phase in 100 ml of GC medium, harvested by centrifugation, and resuspended in 5 ml buffer (20% w/v sucrose, 50 mM Tris-HCl, 50 mM EDTA, pH8) After 10 minutes incubation on ice, the bacteria were lysed by adding 10 ml of lysis solution (50 mM NaCl, 1% Na-Sarkosyl, 50 μg/ml Proteinase K), and the suspension incubated at 37° C. for 2 hours. Two phenol extractions (equilibrated to pH 8) and one CHCl3/isoamylalcohol (24:1) extraction were performed. DNA was precipitated by addition of 0.3M sodium acetate and 2 volumes of ethanol, and collected by centrifugation. The pellet was washed once with 70% (v/v) ethanol and redissolved in 4.0 ml TE buffer (10 mM Tris-HCl, 1 mM EDTA, pH 8.0). The DNA concentration was measured by reading OD260.
The standard PCR protocol was as follows: 200 ng of genomic DNA from 2996, MC581000, or BZ232 strains or 10 ng of plasmid DNA preparation of recombinant clones were used as template in the presence of 40 μM of each oligonucletide primer, 400-800 μM dNTPs solution, lx PCR buffer (including 1.5 mM NgCl2), 2.5 units TaqI DNA polymerase (using Perkin-Elmer AmpliTaQ, Boerhingher Mannheim Expand Long Template).
After a preliminary 3 minute incubation of the whole mix at 95° C., each sample underwent a two-step amplification: the first 5 cycles were performed using the hybridisation temperature that excluded the restriction enzyme tail of the primer (Tm1). This was followed by 30 cycles according to the hybridisation temperature calculated for the whole length oligos (Tm2). Elongation times, performed at 68° C. or 72° C., varied according to the length of the Orf to be amplified. In the case of Orf1 the elongation time, starting from 3 minutes, was increased by 15 seconds each cycle. The cycles were completed with a 10 minute extension step at 72° C.
The amplified DNA was either loaded directly on a 1% agarose gel. The DNA fragment corresponding to the band of correct size was purified from the gel using the Qiagen Gel Extraction Kit, following the manufacturer's protocol.
The purified DNA corresponding to the amplified fragment was digested with the appropriate restriction enzymes for cloning into pET-21b+, pET22b+ or pET-24b+. Digested fragments were purified using the QIAquick PCR purification kit (following the manufacturer's instructions) and eluted with either H2O or 10 mM Tris, pH 8.5. Plasmid vectors were digested with the appropriate restriction enzymes, loaded onto a 1.0% agarose gel and the band corresponding to the digested vector purified using the Qiagen QiAquick Gel Extraction Kit.
The fragments corresponding to each gene, previously digested and purified, were ligated into pET21b+, pET22b+ or pET-24b+. A molar ratio of 3:1 fragment/vector was used with T4 DNA ligase in the ligation buffer supplied by the manufacturer.
Recombinant plasmid was transformed into competent E. coli DH5 or HB101 by incubating the ligase reaction solution and bacteria for 40 minutes on ice, then at 37° C. for 3 minutes. This was followed by the addition of 800 μl LB broth and incubation at 37° C. for 20 minutes. The cells were centrifuged at maximum speed in an Eppendorf microfuge, resuspended in approximately 2000 of the supernatant and plated onto LB ampicillin (100 mg/ml) agar.
Screening for recombinant clones was performed by growing randomly selected colonies overnight at 37° C. in 4.0 ml of LB broth+100 μg/ml ampicillin. Cells were pelleted and plasmid DNA extracted using the Qiagen QIAprep Spin Miniprep Kit, following the manufacturer's instructions. Approximately 1 μg of each individual miniprep was digested with the appropriate restriction enzymes and the digest loaded onto a 1-1.5% agarose gel (depending on the expected insert size), in parallel with the molecular weight marker (1 kb DNA Ladder, GIBCO). Positive clones were selected on the basis of the size of insert.
After cloning each gene into the expression vector, recombinant plasmids were transformed into E. coli strains suitable for expression of the recombinant protein. 1 μl of each construct was used to transform E. coli BL21-DE3 as described above. Single recombinant colonies were inoculated into 2 ml LB+Amp (100 μg/ml), incubated at 37° C. overnight, then diluted 1:30 in 20 ml of LB+Amp (100 μg/ml) in 100 ml flasks, to give an OD600 between 0.1 and 0.2. The flasks were incubated at 30° C. or at 37° C. in a gyratory water bath shaker until OD600 indicated exponential growth suitable for induction of expression (0.4-0.8 OD). Protein expression was induced by addition of 1.0 mM IPTG. After 3 hours incubation at 30° C. or 37° C. the OD600 was measured and expression examined. 1.0 ml of each sample was centrifuged in a microfuge, the pellet resuspended in PBS and analysed by SDS-PAGE and Coomassie Blue staining.
Sequences labelled GATE were cloned and expressed using the GATEWAY Cloning Technology (GIBCO-BRL). Recombinational cloning (RC) is based on the recombination reactions that mediate the integration and excision of phage into and from the E. coli genome, respectively. The integration involves recombination of the attP site of the phage DNA within the attB site located in the bacterial genome (BP reaction) and generates an integrated phage genome flanked by attL and attR sites. The excision recombines attL and attR sites back to attP and attB sites (LR reaction). The integration reaction requires two enzymes [the phage protein Integrase (Int) and the bacterial protein integration host factor (IHF)] (BP clonase). The excision reaction requires Int, IHF, and an additional phage enzyme, Excisionase (His) (LR clonase), Artificial derivatives of the 25-bp bacterial attB recombination site, referred to as B1 and B2, were added to the 5 end of the primers used in PCR reactions to amplify Neisserial ORFs. The resulting products were BP cloned into a “Donor vector” containing complementary derivatives of the phage attP recombination site (P1 and P2) using BP clonase. The resulting “Entry clones” contain ORFs flanked by derivatives of the attL site (L1 and L2) and were subcloned into expression “destination vectors” which contain derivatives of the attL-compatible attR sites (R1 and R2) using LR clonase. This resulted in “expression clones” in which ORFs are flanked by B1 and B2 and fused in frame to the GST or His N terminal tags.
The E. coli strain used for GATEWAY expression is BL21-SI. Cells of this strain are induced for expression of the T7 RNA polymerase by growth in medium containing salt (0.3 M NaCl).
Note that this system gives N-terminus His tags.
Fractions composed principally of either inner, outer or total membrane were isolated in order to obtain recombinant proteins expressed with membrane-localisation leader sequences. The method for preparation of membrane fractions, enriched for recombinant proteins, was adapted from Filip et. al. [J. Bact. (1973) 115:717-722] and Davies et. al. [J. Immunol. Meth. (1990) 143:215-225]. Single colonies harbouring the plasmid of interest were grown overnight at 37° C. in 20 ml of LB/Amp (100 μg/ml) liquid culture. Bacteria were diluted 1:30 in 1.0 L of fresh medium and grown at either 30° C. or 37° C. until the OD550 reached 0.6-0.8. Expression of recombinant protein was induced with IPTG at a final concentration of 1.0 mM. After incubation for 3 hours, bacteria were harvested by centrifugation at 8000 g for 15 minutes at 4° C. and resuspended in 20 ml of 20 mM Tris-HCl (pH 7.5) and complete protease inhibitors (Boehringer-Mannheim). All subsequent procedures were performed at 4° C. or on ice.
Cells were disrupted by sonication using a Branson Sonifier 450 and centrifuged at 5000 g for 20 min to sediment unbroken cells and inclusion bodies. The supernatant, containing membranes and cellular debris, was centrifuged at 50000 g (Beckman Ti50, 29000 rpm) for 75 min, washed with 20 mM Bis-tris propane (pH 6.5), 1.0 M NaCl, 10% (v/v) glycerol and sedimented again at 50000 g for 75 minutes. The pellet was resuspended in 20 mM Tris-HCl (pH 7.5), 2.0% (v/v) Sarkosyl, complete protease inhibitor (1.0 mM EDTA, final concentration) and incubated for 20 minutes to dissolve inner membrane. Cellular debris was pelleted by centrifugation at 5000 g for 10 min and the supernatant centrifuged at 75000 g for 75 minutes (Beckman Ti50, 33000 rpm). Proteins 0081, and 519L were found in the supernatant suggesting inner membrane localisation. For these proteins both inner and total membrane fractions (washed with NaCl as above) were used to immunise mice. Outer membrane vesicles obtained from the 75000 g pellet were washed with 20 mM Tris-HCl (pH 7.5) and centrifuged at 75000 g for 75 minutes or overnight. The OMV was finally resuspended in 500 μl of 20 mM Tris-HCl (pH 7.5), 10% v/v glycerol. Orf1L and Orf40L were both localised and enriched in the outer membrane fraction which was used to immunise mice. Protein concentration was estimated by standard Bradford Assay (Bio-Rad), while protein concentration of inner membrane fraction was determined with the DC protein assay (Bio-R ad). Various fractions from the isolation procedure were assayed by SDS-PAGE.
Purification of his-Tagged Proteins
Various forms of 287 were cloned from strains 2996 and MC58. They were constructed with a C-terminus His-tagged fusion and included a mature form (aa 18-427), constructs with deletions (Δ1, Δ2, Δ3 and Δ4) and clones composed of either B or C domains. For each clone purified as a His-fusion, a single colony was streaked and grown overnight at 37° C. on a LB/Amp (100 μg/ml) agar plate. An isolated colony from this plate was inoculated into 20 ml of LB/Amp (100 μg/ml) liquid medium and grown overnight at 37° C. with shaking. The overnight culture was diluted 1:30 into 1.0 L LB/Amp (100 μg/ml) liquid medium and allowed to grow at the optimal temperature (30 or 37° C.) until the OD550 reached 0.6-0.8. Expression of recombinant protein was induced by addition of IPTG (final concentration 1.0 mM) and the culture incubated for a further 3 hours. Bacteria were harvested by centrifugation at 8000 g for 15 min at 4° C. The bacterial pellet was resuspended in 7.5 ml of either (i) cold buffer A (300 mM NaCl, 50 mM phosphate buffer, 10 mM imidazole, pH 8.0) for soluble proteins or (ii) buffer B (10 mM Tris-HCl, 100 mM phosphate buffer, pH 8.8 and, optionally, 8M urea) for insoluble proteins. Proteins purified in a soluble form included 287-His, Δ1, Δ2, Δ3 and Δ4287-His, Δ4287MC58-His, 287c-His and 287cMC58-His. Protein 287bMC58-His was insoluble and purified accordingly. Cells were disrupted by sonication on ice four times for 30 sec at 40 W using a Branson sonifier 450 and centrifuged at 13000×g for 30 ruin at 4° C. For insoluble proteins, pellets were resuspended in 2.0 ml buffer C (6 M guanidine hydrochloride, 100 mM phosphate buffer, 10 mM Tris-HCl, pH 7.5 and treated with 10 passes of a Dounce homogenizer. The homogenate was centrifuged at 13000 g for 30 min and the supernatant retained. Supernatants for both soluble and insoluble preparations were mixed with 150 μl Ni2+-resin (previously equilibrated with either buffer A or buffer B, as appropriate) and incubated at room temperature with gentle agitation for 30 min. The resin was Chelating Sepharose Fast Flow (Pharmacia), prepared according to the manufacturer's protocol. The batch-wise preparation was centrifuged at 700 g for 5 min at 4° C. and the supernatant discarded. The resin was washed twice (batch-wise) with 10 ml buffer A or B for 10 min, resuspended in 1.0 nil buffer A or B and loaded onto a disposable column. The resin continued to be washed with either (i) buffer A at 4° C. or (ii) buffer B at room temperature, until the OD280 of the flow-through reached 0.02-0.01. The resin was further washed with either (i) cold buffer C (300 mM NaCl, 50 mM phosphate buffer, 20 mM imidazole, pH 8.0) or (ii) buffer D (10 mM Tris-Ha, 100 mM phosphate buffer, pH 6.3 and, optionally, 8M urea) until OD280 of the flow-through reached 0.02-0.01. The His-fusion protein was eluted by addition of 700 μl of either (i) cold elution buffer A (300 mM NaCl, 50 mM phosphate buffer, 250 mM imidazole, pH 8.0) or (ii) elution buffer B (10 mM Tris-HCl, 100 mM phosphate buffer, pH 4.5 and, optionally, 8M urea) and fractions collected until the OD280 indicated all the recombinant protein was obtained. 20 μl aliquots of each elution fraction were analysed by SDS-PAGE. Protein concentrations were estimated using the Bradford assay.
Renaturation of Denatured his-Fusion Proteins.
Denaturation was required to solubilize 287bMC8, so a renaturation step was employed prior to immunisation. Glycerol was added to the denatured fractions obtained above to give a final concentration of 10% v/v. The proteins were diluted to 200 μg/ml using dialysis buffer I (10% v/v glycerol, 0.5M arginine, 50 mM phosphate buffer, 5.0 mM reduced glutathione, 0.5 mM oxidised glutathione, 2.0M urea, pH 8.8) and dialysed against the same buffer for 12-14 hours at 4° C. Further dialysis was performed with buffer II (10% v/v glycerol, 0.5M arginine, 50 mM phosphate buffer, 5.0 mM reduced glutathione, 0.5 mM oxidised glutathione, pH 8.8) for 12-14 hours at 4° C. Protein concentration was estimated using the formula:
Protein (mg/ml)=(1.55×OD280)−(0.76×OD260)
Automated sequence analysis of the NH2-terminus of proteins was performed on a Beckman sequencer (LF 3000) equipped with an on-line phenylthiohydantoin-amino acid analyser (System Gold) according to the manufacturer's recommendations.
Balb/C mice were immunized with antigens on days 0, 21 and 35 and sera analyzed at day 49.
The acapsulated MenB M7 and the capsulated strains were plated on chocolate agar plates and incubated overnight at 37° C. with 5% CO2. Bacterial colonies were collected from the agar plates using a sterile dracon swab and inoculated into Mueller-Hinton Broth (Difco) containing 0.25% glucose. Bacterial growth was monitored every 30 minutes by following OD620. The bacteria were let to grow until the OD reached the value of 0.4-0.5. The culture was centrifuged for 10 minutes at 4000 rpm. The supernatant was discarded and bacteria were washed twice with PBS, resuspended in PBS containing 0.025% formaldehyde, and incubated for 1 hour at 37° C. and then overnight at 4° C. with stirring. 100 μl bacterial cells were added to each well of a 96 well Greiner plate and incubated overnight at 4° C. The wells were then washed three times with PBT washing buffer (0.1% Tween-20 in PBS). 200 μl of saturation buffer (2.7% polyvinylpyrrolidone 10 in water) was added to each well and the plates incubated for 2 hours at 37° C. Wells were washed three times with PBT. 200 μl of diluted sera (Dilution buffer; 1% BSA, 0.1% Tween-20, 0.1% NaN3 in PBS) were added to each well and the plates incubated for 2 hours at 37° C. Wells were washed three times with PBT. 100 μl of HRP-conjugated rabbit anti-mouse (Dako) serum diluted 1:2000 in dilution buffer were added to each well and the plates were incubated for 90 minutes at 37° C. Wells were washed three times with PBT buffer. 100 μl of substrate buffer for HRP (25 ml of citrate buffer pH5, 10 mg of O-phenildiamine and 10 μl of H2O2) were added to each well and the plates were left at room temperature for 20 minutes. 100 μl 12.5% H2SO4 was added to each well and OD490 was followed. The ELISA titers were calculated abitrarely as the dilution of sera which gave an OD490 value of 0.4 above the level of preimmune sera. The ELISA was considered positive when the dilution of sera with OD49 of 0.4 was higher than 1:400.
The acapsulated MenB M7 strain was plated on chocolate agar plates and incubated overnight at 37° C. with 5% CO2. Bacterial colonies were collected from the agar plates using a sterile dracon swab and inoculated into 4 tubes containing 8 ml each Mueller-Hinton Broth (Difco) containing 025% glucose. Bacterial growth was monitored every 30 minutes by following OD620. The bacteria were let to grow until the OD reached the value of 0.35-0.5. The culture was centrifuged for 10 minutes at 4000 rpm. The supernatant was discarded and the pellet was resuspended in blocking buffer (1% BSA in PBS, 0.4% NaN3) and centrifuged for 5 minutes at 4000 rpm. Cells were resuspended in blocking buffer to reach OD620 of 0.05. 100 μl bacterial cells were added to each well of a Costar 96 well plate. 100 μl of diluted (1:100, 1:200, 1:400) sera (in blocking buffer) were added to each well and plates incubated for 2 hours at 4° C. Cells were centrifuged for 5 minutes at 4000 rpm, the supernatant aspirated and cells washed by addition of 200 μl/well of blocking buffer in each well, 100 μl of R-Phicoerytrin conjugated F(ab)2 goat anti-mouse, diluted 1:100, was added to each well and plates incubated for 1 hour at 4° C. Cells were spun down by centrifugation at 4000 rpm for 5 minutes and washed by addition of 200 μl/well of blocking buffer. The supernatant was aspirated and cells resuspended in 200 μl/well of PBS, 0.25% formaldehyde. Samples were transferred to FACScan tubes and read. The condition for FACScan (Laser Power 15 mW) setting were: FL2 on; FSC-H threshold: 92; FSC PMT Voltage: E 01; SSC PMT: 474; Amp. Gains 6.1; FL-2 PMT: 586; compensation values: 0.
N. meningitidis strain 2996 was grown overnight at 37° C. on chocolate agar plates (starting from a frozen stock) with 5% CO2. Colonies were collected and used to inoculate 7 ml Mueller-Hinton broth, containing 0.25% glucose to reach an OD620 of 0.05-0.08. The culture was incubated for approximately 1.5 hours at 37 degrees with shacking until the OD620 reached the value of 0.23-0.24. Bacteria were diluted in 50 mM Phosphate buffer pH 7.2 containing 10 mM MgCl2, 10 mM CaCl2 and 0.5% (w/v) BSA (assay buffer) at the working dilution of 105 CFU/ml. The total volume of the final reaction mixture was 50 μl with 25 μl of serial two fold dilution of test serum, 12.5 μl of bacteria at the working dilution, 12.5 μl of baby rabbit complement (final concentration 25%).
Controls included bacteria incubated with complement serum, immune sera incubated with bacteria and with complement inactivated by heating at 56° C. for 30′. Immediately after the addition of the baby rabbit complement, 10 μl of the controls were plated on Mueller-Hinton agar plates using the tilt method (time 0). The 96-wells plate was incubated for 1 hour at 37° C. with rotation. 7 μl of each sample were plated on Mueller-Hinton agar plates as spots, whereas 10 μl of the controls were plated on Mueller-Hinton agar plates using the tilt method (time 1). Agar plates were incubated for 18 hours at 37 degrees and the colonies corresponding to time 0 and time 1 were counted.
Purified proteins (500 ng/lane), outer membrane vesicles (5 μg) and total cell extracts (25 μg) derived from MenB strain 2996 were loaded onto a 12% SDS-polyacrylamide gel and transferred to a nitrocellulose membrane. The transfer was performed for 2 hours at 150 mA at 4° C., using transfer buffer (0.3% Tris base, 1.44% glycine, 20% (v/v) methanol). The membrane was saturated by overnight incubation at 4° C. in saturation buffer (10% skimmed milk, 0.1% Triton X100 in PBS). The membrane was washed twice with washing buffer (3% skimmed milk, 0.1% Triton X100 in PBS) and incubated for 2 hours at 37° C. with mice sera diluted 1:200 in washing buffer. The membrane was washed twice and incubated for 90 minutes with a 1:2000 dilution of horseradish peroxidase labelled anti-mouse Ig. The membrane was washed twice with 0.1% Triton X100 in PBS and developed with the Opti-4CN Substrate Kit (Bio-Rad). The reaction was stopped by adding water.
The OMVs were prepared as follows: N. meningitidis strain 2996 was grown overnight at 37 degrees with 5% CO2 on 5 GC plates, harvested with a loop and resuspended in 10 ml of 20 mM Tris-HCl pH 7.5, 2 mM EDTA. Heat inactivation was performed at 56° C. for 45 minutes and the bacteria disrupted by sonication for 5 minutes on ice (50% duty cycle, 50% output, Branson sonifier 3 mm microtip). Unbroken cells were removed by centrifugation at 5000 g for 10 minutes, the supernatant containing the total cell envelope fraction recovered and further centrifuged overnight at 50000 g at the temperature of 4° C. The pellet containing the membranes was resuspended in 2% sarkosyl, 20 mM Tris-HCl pH 7.5, 2 mM EDTA and incubated at room temperature for 20 minutes to solubilise the inner membranes. The suspension was centrifuged at 10000 g for 10 minutes to remove aggregates, the supernatant was further centrifuged at 50000 g for 3 hours. The pellet, containing the outer membranes was washed in PBS and resuspended in the same buffer. Protein concentration was measured by the D.C. Bio-Rad Protein assay (Modified Lowry method), using BSA as a standard′.
Total cell extracts were prepared as follows: N. meningitidis strain 2996 was grown overnight on a GC plate, harvested with a loop and resuspended in 1 ml of 20 mM Tris-HCl. Heat inactivation was performed at 56° C. for 30 minutes.
Cellular Fractions Preparation
Total lysate, periplasm, supernatant and OMV of E. coli clones expressing different domains of 961 were prepared using bacteria from over-night cultures or after 3 hours induction with IPTG. Briefly, the periplasm were obtained suspending bacteria in saccarose 25% and Tris 50 mM (pH 8) with polimixine 100 μg/ml. After 1 hr at room temperature bacteria were centrifuged at 13000 rpm for 15 min and the supernatant were collected. The culture supernatant were filtered with 0.2 μm and precipitated with TCA 50% in ice for two hours. After centrifugation (30 min at 13000 rp) pellets were rinsed twice with ethanol 70% and suspended in PBS. The OMV preparation was performed as previously described. Each cellular fraction were analyzed in SUS-PAGE or in Western Blot using the polyclonal anti-serum raised against GST-961.
Adhesion Assay
Chang epithelial cells (Wong-Kilbourne derivative, clone 1-5c-4, human conjunctiva) were maintained, in DMEM (Gibco) supplemented with 10% heat-inactivated FCS, 15 mM L-glutamin′ e and antibiotics.
For the adherence assay, sub-confluent culture of Chang epithelial cells were rinsed with PBS and treated with trypsin-EDTA (Gibco), to release them from the plastic support. The cells were then suspended in PBS, counted and dilute in PBS to 5×105 cells/ml.
Bacteria from over-night cultures or after induction with IPTG, were pelleted and washed twice with PBS by centrifuging at 13000 for 5 min. Approximately 2-3×108 (cfu) were incubated with 0.5 mg/ml FITC (Sigma) in 1 ml buffer containing 50 mM NaHCO3 and 100 mM NaCl pH 8, for 30 min at room temperature in the dark. FITC-labeled bacteria were wash 2-3 times and suspended in PBS at 1-1.5×109/ml. 200 μl of this suspension (2-3×108) were incubated with 2000 (1×105) epithelial cells for 30 min a 37° C. Cells were than centrifuged at 2000 rpm for 5 min to remove non-adherent bacteria, suspended in 200 μl of PBS, transferred to FACScan tubes and read
| Number | Date | Country | Kind |
|---|---|---|---|
| 0004695.3 | Feb 2000 | GB | national |
| 0027675.8 | Nov 2000 | GB | national |
This application is a Continuation of U.S. application Ser. No. 14/244,806, filed Apr. 3, 2014; which is a Continuation of U.S. application Ser. No. 13/340,549, filed Dec. 29, 2011, now U.S. Pat. No. 8,703,914; which is a Divisional of U.S. application Ser. No. 12/825,210, filed Jun. 28, 2010, now U.S. Pat. No. 8,114,960; which is a Divisional of U.S. application Ser. No. 10/220,481, which claims an international filing date of Feb. 28, 2001, now U.S. Pat. No. 7,803,387; which is the National Phase of PCT Application No. PCT/IB2001/000452, filed Feb. 28, 2001; which claims the benefit of GB Application No. 0027675.8, filed Nov. 13, 2000, and GB Application No. 0004695.3, filed Feb. 28, 2000; all of which are incorporated herein by reference in their entirety.
| Number | Date | Country | |
|---|---|---|---|
| Parent | 12825210 | Jun 2010 | US |
| Child | 13340549 | US | |
| Parent | 10220481 | Aug 2003 | US |
| Child | 12825210 | US |
| Number | Date | Country | |
|---|---|---|---|
| Parent | 14244806 | Apr 2014 | US |
| Child | 15368435 | US | |
| Parent | 13340549 | Dec 2011 | US |
| Child | 14244806 | US |
