METHOD OF INHIBITING C5 CLEAVAGE

Abstract

The invention relates to complement inhibitors that inhibit both the classical and alternative complement pathways. In particular, the invention relates to complement inhibitors derived from the salivary glands of haematophagous arthropods that inhibit both the classical and alternative complement pathways. The invention also relates to the use of the complement inhibitors in the treatment and prevention of diseases.

Claims

1-40. (canceled)

41. A method for producing a protein comprising culturing a host cell comprising a nucleic acid molecule comprising a nucleotide sequence encoding the protein under conditions whereby said protein is expressed, and recovering said protein thus produced, wherein the protein is a complement inhibitor molecule comprising: i) an amino acid sequence with at least 90% sequence identity to amino acids 19 to 168 of SEQ ID NO: 2, or ii) an amino acid sequence with at least 90% sequence identity to amino acids 1 to 168 of SEQ ID NO: 2.

42. The method of claim 1 wherein the complement inhibitor molecule comprises amino acids 19 to 168 of SEQ ID NO: 2.

43. The method of claim 1 wherein the complement inhibitor molecule comprises amino acids 1 to 168 of SEQ ID NO: 2.

44. The method of claim 1 wherein the complement inhibitor molecule consists of amino acids 19 to 168 of SEQ ID NO: 2.

45. The method of claim 1 wherein the complement inhibitor molecule consists of amino acids 1 to 168 of SEQ ID NO: 2.

46. The method of claim 1 wherein the nucleotide sequence encoding the complement inhibitor is a sequence with at least 90% sequence identity to nucleotides 55 to 507 of SEQ ID NO: 1.

47. The method of claim 1 wherein the nucleotide sequence encoding the complement inhibitor is a sequence with at least 90% sequence identity to nucleotides 1 to 507 of SEQ ID NO: 1.

48. The method of claim 1 wherein the nucleotide sequence encoding the complement inhibitor is a sequence comprising nucleotides 55 to 507 of SEQ ID NO: 1.

49. The method of claim 1 wherein the nucleotide sequence encoding the complement inhibitor is a sequence comprising nucleotides 1 to 507 of SEQ ID NO: 1.

50. The method of claim 1 wherein the nucleotide sequence encoding the complement inhibitor is a sequence consisting of nucleotides 55 to 507 of SEQ ID NO: 1.

51. The method of claim 1 wherein the nucleotide sequence encoding the complement inhibitor is a sequence consisting of nucleotides 1 to 507 of SEQ ID NO: 1.

52. The method of claim 1 wherein the complement inhibitor is a fusion protein comprising a complement inhibitor molecule and another polypeptide.

53. The method of claim 1, wherein the nucleic acid molecule encoding the complement inhibitor is present in a vector.

54. The method of claim 1, wherein the host cell is a prokaryotic cell.

55. The method of claim 1, wherein the host cell is an E. coli cell.

56. The method of claim 1, wherein the host cell is a eukaryotic cell.

57. The method of claim 1, wherein the host cell is a yeast cell.

58. The method of claim 1, wherein the host cell is a mammalian cell.

59. The method of claim 1, wherein the host cell is an insect cell.

60. The method of claim 1, wherein the nucleic acid molecule is introduced into the host cell via transfection or transformation.

61. The method of claim 1, wherein the nucleic acid molecule is introduced to the host cell transiently.

62. The method of claim 1, wherein the nucleic acid molecule is introduced to the host cell permanently.

Description

BRIEF DESCRIPTION OF FIGURES

[0077] FIG. 1: Schematic diagram of classical and alternative pathways of complement activation. Enzymatic components, dark grey. Anaphylatoxins enclosed in starbursts.

[0078] FIG. 2A: Purification of O. moubata complement inhibitor (OmCI). Cation exchange chromatography. Peak containing inhibitor indicated by arrowhead.

[0079] FIG. 2B: Purification of O. moubata complement inhibitor (OmCI). Classical haemolytic assay. Sample 1 (black bar), 100% lysis; sample 2, 0% lysis; sample 3, (cross-hatched bar) serum only; sample 4, serum plus 1 l SGE; samples 5-23 (grey bars) serum plus 10 l fractions 10-28 shown in FIG. 2A. Average of 3 replicates.

[0080] FIG. 3A: Analysis of purified OmCI by denaturing SDS-PAGE.

[0081] FIG. 3B: Analysis of purified OmCI by isoelectric focusing (IEF).

[0082] FIG. 3C: Analysis of purified OmCI by high pressure liquid chromatography (HPLC). Fractions f15 and f17 in FIG. 3A and FIG. 3B are the same. Fraction f15 was recovered and analysed by HPLC, FIG. 3C. Size markers and isoelectric point (PI) markers are indicated at left of FIG. 3A and FIG. 3B.

[0083] FIG. 4: Primary sequence of OmCI. Signal sequence underlined. Cysteine residues in bold type. Nucleotide and amino acid number indicated at right. The nucleic acid sequence (SEQ ID NO: 1) and the amino acid sequence (SEQ ID NO: 2) are depicted.

[0084] FIG. 5: Clustal X sequence alignment of OmCI with tick salivary gland proteins 2 and 3 (TSGP2 and 3) and moubatin. Identical residues are highlighted in grey (cysteines in black) and asterisked. The amino acid sequences are designated as follows: OmCI (SEQ ID NO: 6); TSGP3 (SEQ ID NO: 7); TSGP2 (SEQ ID NO: 8); and Moubatin (SEQ ID NO: 9).

[0085] FIG. 6A: Inhibitory activity in supernatant of yeast clones with OmCI inserted into genome (13.1-13.5, and clone with vector only inserted into genome (control).

[0086] FIG. 6B: Inhibitory activity in cell pellet of yeast clones with OmCI inserted into genome (13.1-13.5), and clone with vector only inserted into genome (control).

[0087] FIG. 7A Expression of yeast cell expressed rOmCI. SDS PAGE of fractions 9-13 from Superdex-75 gel filtration column.

[0088] FIG. 7B: Deglycosylation of yeast cell expressed rOmCI. Effect of PNGaseF treatment on mobility of highly glycosylated rOmCI (fractions 9-11 in FIG. 7A). Arrows indicate PNGaseF (upper arrow) and native OmCI (lower arrow). EV504 is distantly related to OmCI and is known to be glycosylated. Size markers (kDa) indicated at left of panel.

[0089] FIG. 8: Inhibition of lysis caused by classical (CH50) and alternative (AH50) pathways of complement activation by different concentrations of native OmCI. Average of 4 replicates.

[0090] FIG. 9: Effect of OmCI on addition of C8 and C9 to partially formed membrane attack complex (MAC). Absorbance due to 100% and 0% lysis and in absence (PBS) and presence (SGE) of inhibitor shown. Average of 6 replicates.

[0091] FIG. 10A: Timecourse showing absence of effect of OmCI on classical pathway cleavage of C3a from C3c analysed by denaturing SDS-PAGE. Minutes (min) since start of reaction indicated. Reactions performed with (OmCI) or without (PBS) inhibitor, or in presence of 10 mM EDTA. Positions of bovine serum albumin (BSA) and haemoglobin (HAE) shown. Size markers (kDa) indicated at left of panel.

[0092] FIG. 10B: Timecourse showing absence of effect of OmCI on classical pathway cleavage of C3a from C3c analysed by immunoblot with C3A specific antisera. As FIG. 10A, positions of C3a and C3c shown.

[0093] FIG. 11: Effect of OmCI on classical, alternative and cobra venom factor (CVF) C5 convertase cleavage of C5a from C5 analysed by ELISA. Picograms/l C5a released measured after 100% lysis of sheep red blood cells with water, 0% lysis in GVB.sup.2+ only, and reactions with (OmCI) or without (PBS) inhibitor. Average of 4 replicates.

[0094] FIG. 12: Effect of addition of pure C3 and C5 to C3 and C5 depleted sera on classical pathway lysis of sheep red blood cells in presence (+) and absence () of minimal amount of OmCI that gave complete inhibition of lysis at 1 log fold excess. Average of 4 replicates.

[0095] FIG. 13: Effect of boiling on inhibitory activity of OmCI in CH50 assay.

[0096] FIG. 14: Effect of pH treatment on inhibitory activity of OmCI in CH50 assay.

[0097] FIG. 15: Detection of C5 binding to nOmCI. nOmCI and RaHBP2 (control) transferred to nitrocellulose were probed with I.sup.125 labelled C3 or C5 then autoradiogrammed. Protein size markers (kDa) indicated at left of panel.

[0098] FIG. 16A: Detection of nOmCI binding to C5 by gel filtration chromatography. Radiolabelled nOmCI with or without purified C3 and C5 (pure C3/C5).

[0099] FIG. 16B: Detection of nOmC1 binding to C5 by gel filtration chromatography. Radiolabelled nOmCI with or without NHS, and C3 or C5 depleted sera (delta C3/C5). Protein size markers (kDa) indicated by arrows.

EXAMPLES

Materials and Methods

Materials

[0100] Sheep and rabbit red blood cells were from Tissue Culture Services, Haemolysin, pooled normal human sera (NHS) and depleted sera were all obtained from Sigma. Guinea pig sera were from in house animals. Pure C3, C4, C5, C8 and C9, and factors B and D, were purchased from Calbiochem. Anti-human C3a rabbit polyclonal antisera was from Calbiochem and cobra venom factor (CVF) from Quidel. The C5a ELISA detection kit was purchased from Immuno-Biological Laboratories (IBL).

Ticks

[0101] Ornithodorus moubata ticks were reared according to Jones et al. (1988).

Salivary Gland Sample Preparation and Purification

[0102] Salivary glands were dissected under a microscope, rinsed briefly in cold PBS buffer (0.01M phosphate buffer and 0.15M NaCl pH 7.2) and transferred to Eppendorf vials standing in dry ice and stored frozen at 20 C. When needed, 30 pairs of salivary glands were defrosted and disrupted in 500 l PBS using a 1 ml Dounce homogenisor. The homgenate was centrifuged at 15K RPM in a benchtop centrifuge and the supernatant (referred to as salivary gland extract, SGE) was collected and stored at 70 C., or tested for complement inhibitory activity and used for isolation of the active fraction.

Classical Pathway of Complement Haemolytic Assay (CH50)

[0103] Five ml of fresh sheep blood in Alsever's solution (1:1 vol/vol) were washed once in 50 ml Gelatin veronal barbital-EDTA (GVB-EDTA) and three times in 50 ml GVB.sup.2+ buffer (GVB buffer with Mg.sup.2+ and Ca.sup.2+). The blood was diluted to a concentration of 110.sup.9 cells ml.sup.1. The erythrocytes were sensitised using rabbit haemolysin, titrated as described (Coligan, 1994). Assays were carried in a total volume of 200 l using 100 l 1:40 of diluted NHS or guinea pig sera in GVB.sup.2+ as a source of complement and 100 l 210.sup.8 sensitised erythrocytes (EA) in accordance with standard protocols (Giclas, 1994). SGE, native or recombinant OmCI (nOmCI or rOmCI) or PBS (1-5 l) was added last, and the reactions incubated at 37 C. At the end of the timecourse (up to 32 min) whole cells were spun down 12000g for 5 seconds and hemolysis measured spectrophotometrically at 412 nm (Coligan, 1994). All assays were carried out at least three times.

Alternative Pathway of Complement Hemolytic Assay (AH50)

[0104] Five ml of fresh rabbit blood in Alsever's solution (1:1 vol/vol) were washed three times in 50 ml GVB/Mg (10 mM) EGTA buffer by centrifuging at 1500g for 10 mins between washes. The rabbit blood was diluted to 210.sup.8 cells ml.sup.1. NHS was diluted in GVB/Mg EGTA buffer. The assay volume was made up to 150 l with 50 l prepared blood. 1-5 l of SGE, PBS, native OmCI or recombinant OmCI was added to the reactions last, and the reactions incubated at 37 C. At the end of the timecourse (up to 60 min) whole cells were spun down 12000g for 5 seconds and haemolysis measured spectrophotometrically at 412 nm (Coligan, 1994). All assays were carried out at least three times.

Lytic Assays Using Sera Depleted in Specific Complement Components

[0105] Depleted human sera were used in accordance with the manufacturer's instructions but the total volume of each reaction was reduced to 200 l. Volumes and dilutions of pure complement components that gave 90% lysis were determined empirically. Reactions were incubated for 30 mins at 37 C. All assays were carried out at least three times.

[0106] Purification of O. moubata complement inhibitor (OmCI) from SGE 150 l SGE were diluted in 5 ml 25 mM sodium phosphate buffer pH 6.8, 50 mM NaCl and loaded onto a 1 ml Q-SEPHAROSE HP cation exchange column (Pharmacia) at a flow rate of 1 ml/min. After washing with a further 10 column volumes of running buffer, bound proteins were eluted using a 40 min 0.05-0.75M NaCl gradient at a flow rate of 0.5 ml/min and monitored at 280 nm. One ml fractions were collected and 10 l assayed for complement inhibitory activity in 200 l total volume CH50 assays. Representative active and inactive fractions were concentrated to 50 l using Centricon 3 filtration devices (Amicon), 2 ml PBS was added, the fractions were concentrated to 50 l again and 1.5 l of each was run on a 4-12% Tris-Tricine denaturing SDS gel (Invitrogen). Five l per lane of both active and inactive fractions were run on a pH 3-7 IEF gel (Invitrogen) and electroblotted to IMMOBILON-P (Mllipore) using 0.7% acetic acid. The membrane was stained with Ponceau-S, and major bands excised and eluted in 200 l, 50 mM Tris pH 8, 2% TRITON X-100 (polyethylene glycol tert-octylphenyl ether) by vortexing for 1 min and centrifuging for 10 min at 15 K rpm three times. The TRITON X-100 was removed by repurifying the proteins on Q-SEPHAROSE columns using the conditions described above. After Centricon 3 concentration and buffer exchange to PBS, samples were assayed for complement inhibitory activity and examined on 4-12% gels or subjected to HPLC fractionation and protein sequence analysis.

Detection of C3a Production During Haemolytic Assays

[0107] CH50/AH50 assays were set up in a total volume of 200 l using a 1:80 final dilution of NHS or guinea pig sera with or without native OmCI. Reactions placed at 37 C. were removed from the waterbath at specified time points, then spun at 12000 g for 10 seconds and the supernatant removed for subsequent analysis by immunoblotting. 10 l of each reduced supernatant sample was electrophoresed on 4-12% Bis-Tris gel run with MES running buffer (Invitrogen) then transferred to nitrocellulose. Confirmation of equal loading and even transfer to all lanes was judged by the intensity of the serum albumin band following Ponceau staining. C3a cleavage from C3 was detected by immunoblot using anti-human C3a rabbit monospecific antisera (Calbiochem). The nitrocellulose membrane was blocked overnight with phosphate buffered saline 0.1% TWEEN 20 (polysorbate 20), 5% non-fat dried milk (PBS). This buffer was used for all subsequent dilutions and washing steps unless indicated otherwise. Anti-C3a antisera was diluted 1:500 and incubated with the membrane for 2 h. The membrane was then washed twice for 20 minutes before adding 1:3000 dilution of anti-rabbit alkaline phosphatase conjugate (Sigma) in PBS. After another 2 h incubation the membrane was washed twice for 5 minutes, rinsed briefly in water and 10 ml BCIP/NBT purple liquid alkaline phosphatase substrate (Sigma) added.

Detection of C5a Production During Haemolytic Assays

[0108] Haemolytic assays were performed as described for detection of C3a. A C5a ELISA kit (IBL) was used to detect cleavage of C5a from C5. To prevent cross-reaction with uncleaved C5, the C5 present in the supernatant from the haemolytic assays was precipitated using the reagent provided by the kit manufacturers. The measuring range of the kit extends from 0.1 to 10 g/L. The lower limit of detection is 0.02 g/L.

Decomplementation of Sera with Cobra Venom Factor (CVF)

[0109] 0.25 g CVF (0.25 g/l stock) and either 1 l native OmCI or 1 l PBS was added to 5 l human sera and incubated for 1 hour at 37 C. Half the CVF treated sera was added to 97.5 l GVB.sup.2+ and 100 l EA. After incubation for 20 mins at 37 C. percentage lysis and concentration of C5a (see above) in reaction supernatants were determined.

HPLC of Active Fraction, Protein Sequence Analysis and Tryptic Digestion

[0110] Twenty l of the active fraction eluted from the IEF resolved protein was run on a Jupiter C4 column/1501.0 mm, and a gradient of 10-40% acetonitrile (ACN) with 0.1% trifluoroacetic acid (TFA), flow rate 1 ml/min with 0.5% ACN/min increments, and monitored at 215 nm. The four close running peaks at c.53 min were transferred to Immobilon-P membrane and sequenced using an Applied Biosystems Mini-Blott cartridge. Twenty five cycles were performed on each protein.

[0111] For sequence analysis of tryptic digestion products, the major peak at 53 min (comprising all four peaks observed in the first HPLC separation) was dried down in a SpeedVac and redissolved in 6M guanidine 0.5M Tris pH 8.0, then reduced and alkylated using 4-vinylpyridine. It was then re-run on the same Jupiter C4 column. No change in retention time was noted. The major peak was dried in SpeedVac and redissolved in 0.1M ammonium bicarbonate pH 8.1. Ten l of Pierce immobilised trypsin was added and the mixture incubated at 37 C. for 5 hours with intermittent mixing. The mixture was then spun at 10K rpm and the supernatant was loaded on a 173a microblotting HPLC (Aquapore C18 column/1000.5 mm). Peaks of interest were excised from the membrane and sequenced.

[0112] Fifteen cycles were performed on each protein.

Construction of O. moubata cDNA Library

[0113] Sixty pairs of O. moubata salivary glands collected from nymphs after their 3rd or 4th feed were excised as described above and placed in 1 ml RNAlater (Ambion) (in place of PBS) and stored at 20 C. mRNA was isolated using the FASTTRACK 2.0 mRNA isolation kit (Invitrogen) and cDNA was synthesised using a Stratagene cDNA synthesis kit (Cat#200401-5). After fractionation into large and small cDNAs on a sepharose CL-2B column, the ethanol precipitated cDNA pellets were each resuspended in 3.5 l ddH.sub.20. cDNA yields were approximately 3.0 ng/l and 5 ng/l for the large and small molecules, respectively. All of the remaining large and small cDNAs were ligated into the Stratagene UniZAP XR phage vector (Cat.#237211) and packaged with GIGAPACK III Gold packaging extract. There were 11500 primary plaques in the large cDNA library and 480500 primary plaques in the small cDNA library. After amplification, the titres of the large and small libraries were 1.510.sup.8 pfu/ml and 410.sup.9 pfu/ml, respectively.

[0114] Twenty plaques from each library were picked into 0.5 ml SM buffer (0.1 M NaCl, 8 mM MgS0.sub.4, 50 mM TRIS.HCl pH 7.5, 0.01% gelatin) 1% chloroform and eluted from agarose plugs by vortexing. Phage insert sizes were examined by PCR using T7 (T7 5T AA TAC GAC TCA CTA TAG 3: SEQ ID NO: 10) and T3 (5AAT TAA CCC TCA CTA AAG 3: SEQ ID NO: 11) primers. Each 100 l reaction comprised 2 l eluted phage, 2 l 10 mM dNTPs, 2 l of each primer (from stocks of 0.5 g/ml), 10 l 10REDTaq (Sigma) PCR reaction buffer (100 mM Tris-HCl pH 8.3, 500 mM KCl, 11 mM MgCl.sub.2, 0.1% gelatin), 3 l REDTaq (Sigma) DNA polymerase (1 unit/l in 20 mM Tris-HCl, pH 8.0, 100 mM KCl, 0.1 mM EDTA, 1 mM DTT, 0.5% TWEEN Tween 20 (polysorbate 20), 0.5% IGEPAL CA-630 (octylphenoxypolyethoxyethanol), inert dye, 50% glycerol) and 79 l ddH.sub.2O. Thermal cycling (Hybaid Touchdown thermal cycler) parameters were 194 C. 4 min, 3094 C. 1 min, 48.5 C. 45 s, 72 C. 90 s, and 172 C. 5 min. Agarose gel electrophoresis of the PCR products showed that large library inserts were >1000 base pairs and small library inserts >1000 base pairs.

Cloning cDNA Encoding Complement Inhibitor

[0115] The N-terminal sequences determined for the two major peaks eluting at 53 min from the HPLC were used to design a degenerate primer (OF4) for use with the T7 primer (which binds to the UniZAP XR vector), to amplify the cDNA encoding the complement inhibitor. The sequence of OF4 was 5 GTAC WSN GGN WSN GAR CCN GT 3 (where: N=A or C or G or T; R=G or A; S=G or C; and W=A or T) (SEQ ID NO: 12). The 100 l reaction comprised 3 l large or small cDNA library, 3 l 10 mM dNTPs, 2 l T7 and 4 l OF4 (from stock of 0.5 g/ml), 10 l 10REDTaq PCR reaction buffer, 3 l REDTaq DNA polymerase and 75 l dH.sub.2O. Thermal cycling parameters were 194 C. 4 min, 3094 C. 1 min, 48.5 C. 45 s, 72 C. 90 s, and 172 C. 5 min.

[0116] Agarose gel electrophoresis revealed a range of PCR products. Two products derived from the OF4 primer were purified using a Qiaex II gel extraction kit (Qiagen) and sequenced with an ABI PRISM dye terminator cycle sequencing ready reaction kit and ABI sequencer (Perkin Elmer).

[0117] Conceptual translation of the largest (c.500 bp) and most intense PCR product, derived from the small cDNA library using primer OF4 with T7, revealed a significant BlastX (Altschul et al., 1997) match with the C-terminal sequence of the O. moubata platelet aggregation inhibitor moubatin (Waxman and Connolly, 1993). The sequence extended beyond the stop codon of the cDNA encoding the peptide. A reverse primer (OR1 5 GGG AGG CTT TCT GTA TCC 3; SEQ ID NO: 13) matching the region beyond the stop codon was used with the T3 primer (which binds to the UniZAP XR vector) to obtain the 5 end of the cDNA. The 650 bp PCR product was cloned into the pGEM-T Easy vector (Promega) then sequenced using additional primers OR3 5 CGT CCA ATC GGT TGA AG 3 (SEQ ID NO: 14) and OF6 5 GAC TCG CAA AGT CAT CAC 3 (SEQ ID NO: 15).

Sequence Analysis

[0118] Analyses were carried out using the GCG suite of programs (Wisconsin Package Version 10.1, Genetics Computer Group (GCG), Madison, Wis.) and also the ExPASy (Expert Protein Analysis System) proteomics server of the Swiss Institute of Bioinformatics (expasy.hcuge.ch/). Sequences were compared with the GenBank non-redundant (NR) protein database using the BlastX program (Altschul et al., 1997) and searched against the Pfam (Bateman et al., 2000) and SMART (Schultz et al., 2000) protein domains. Multiple sequence alignment was performed with Clustal X (Jeanmougin et al., 1998).

Yeast Expression and Purification of OmCI

[0119] The OmCI coding region was amplified by means of the polymerase chain reaction (PCR; 95 C. for 30, 50 C. for 30, 72 C. for 30; 18 cycles), using the forward primer OM1Y (5-ATAGAGCTCAAAATGCTGGTTTTGGTGACC-3) (SEQ ID NO: 16) and the reverse primers OR7a (5 ACTGAGCGGCCGCCTAGTGATGGTGATGGTGAT GACCGCAGTCCTTGAGATGGGG 3 (SEQ ID NO: 17) for his-tagged products) or OR6 (5 ACT GAGCGGCCGCCTAGCAGTCCTTGAGATGGGG 3 (SEQ ID NO: 18) non-tagged product). The primers have built-in restriction sites, such that a Sac I site is added upstream of the start codon and a Not I site downstream of the stop codon. The product was ligated between the Sac I and Not I sites of the pMETa C transfer vector (Invitrogen). The plasmidamplified in XL1-Blue cells (Stratagene)was transformed into the Pichia methanolica strains pMAD16 and pMAD11, according to the instructions of the supplier (Invitrogen). Positive clones were grown in Buffered Dextrose-complex Medium BMDY, and protein expression was induced in Buffered Methanol-complex Medium. Protein expression in the supernatant and cells of 6 positive clones was assayed every 24 hours for 5 days by CH50 lytic assay.

[0120] After 96 hours incubation, 500 ml yeast cell media was centrifuged at 6370 g for 15 mins and the inhibitor precipitated from the supernatant by addition of 30% (w/v) PEG-8000 and stirring on ice for 1 hour. Following centrifugation at 23700 g for 1 hour the protein pellet was resuspended in 50 ml 25 mM sodium phosphate buffer pH 6.8, 50 mM NaCl before centrifuging at 6,000 rpm to remove insoluble material. The clarified solution was applied to a 1 ml Q-SEPHAROSE HP cation exchange column and complement inhibitory activity of fractions determined as described above. Active fractions were pooled and exchanged to 300 l PBS using Centricon 3 filtration devices (Amicon), centrifuged at 18900 g for 10 minutes then applied to a Superdex 75 column (Pharmacia) at a flow rate of 0.5 ml/min using 20 mM Tris pH 7.6, 200 mM NaCl as running buffer. 0.5 ml fractions were monitored at 280 nm and collected for 30 minutes. 5 l of each fraction was assayed for inhibitory activity and active fractions exchanged to PBS before visualisation by denaturing SDS-PAGE.

[0121] Purified rOmCI was treated with peptide N-glycosidase F (PNGaseF) in accordance with the manufacturer's instructions (New England Biolabs). Deglycosylated rOmCI was repurified by gel filtration as described above. Five inhibitory fractions were identified by CH50 and 15 l of each was run on SDS PAGE under denaturing and non-denaturing conditions.

Thermostability and pH Stability of Native OmCI

[0122] The minimal amount of native OmCI that inhibits classical pathway mediated cell lysis by c.90% at a 1:40 dilution of guinea pig serum was determined to be 25 ng in a total reaction volume of 100 l. To examine thermostability, 1 l native OmCI (250 ng) was diluted in 9 l PBS. Samples were boiled for 0, 3, 9 or 27 min, cooled rapidly on ice, and 1 l (25 ng) added to 100 l CH50 assays (1:40 guinea pig serum dilution). To examine pH stability, 1 l native OmCI (250 ng) was diluted in 9 l 10 mM sodium acetate (pH 4.5 and 5.5), 10 mM Tris.Cl (pH 7 and 8.2) or 10 mM CAPS (pH 10 and 11) buffer. After incubation for 30 min at 37 C., 1 l (25 ng) was added to 100 l CH50 assays (1:40 guinea pig serum dilution). Controls included 1 l of each of the buffers only in the presence and absence of 1:40 serum dilution. All assays were done in triplicate.

Method for detection of C5 binding to OmCI

[0123] 0.5 g native OmCI and 5 g RaHBP2 were subjected to non-denaturing SDS-PAGE, then transferred to nitrocellulose and blocked overnight in PBS, 0.05% TWEEN 20 (polysorbate 20), 5% non-fat dried milk (PBS). C3 and C5 were labelled with 1125 using Iodogen in accordance with the manufacturer's instructions (Pierce). Blots were incubated with 2 g 1125 labelled C3 (1440 kcpm/min), and 2 g 1125 labelled C5 (2160 kcpm/min) in 15 ml PBS for 4 hours at room temperature. After 320 min washes in PBS at room temperature the nitrocellulose membranes were dried, and autoradiogrammed.

[0124] For gel filtration chromatography, 0.07 g I.sup.125 labelled OmCI (1687 kcpm/min) was incubated with 2 g pure C3 or C5, or 23.8 l NHS or C3 or C5 depleted serum. PBS was added a total volume of 100 l and the mixture incubated for 10 min before chromatography through a Superose 12 10/30 column at a flow rate of 1 ml/min PBS. 1 ml fractions were collected and cpm measured at set distance from a hand held Geiger counter.

Results

[0125] Purification and Identification of Active Fractions from O. moubata SGE

[0126] Following cation exchange chromatography, the active fraction eluted at 0.25M NaCl (FIGS. 2a and b, arrow). The active fraction a control fraction (FIG. 3a) were electroblotted from an IEF gel (FIG. 3b) to a PVDF membrane which was stained with Ponceau-S. The major bands were excised, eluted, repurified by cation exchange chromatography and assayed for complement inhibitory activity. Denaturing SDS PAGE showed the inhibitory activity to be associated with a triplet of proteins with masses of around 19 kDa (FIG. 3a). IEF showed the inhibitory activity to be associated with a single dominant band with a pi of approximately 4.2 (FIG. 3b, upperband carryover from fraction 17). HPLC of the PVDF eluted fraction revealed four adjacent peaks (FIG. 3c). A 17 amino acid N-terminal sequence (DSESDXSGSEPVDAFQA) (SEQ ID NO: 19) obtained from the largest peak (FIG. 3c, peak D) was used to design degenerate primers that generated a PCR product from O. moubata cDNA library which matched the N-terminal sequence.

Primary Structure of the cDNA Encoding OmCI

[0127] The sequence of the full-length clone shows that OmCI is 168 amino acids long (FIG. 4). The protein has an N-terminal secretion signal comprising the first 18 residues. N-terminal sequence analysis indicates the signal peptide cleavage site is between Ala18 and Asp19. The predicted molecular weight of the mature protein is 16.77 kDa and the isoelectric point 4.3. There are two predicted N-glycosylation sites (Asn78 and Asn102) and twelve potential phosphorylation sites (Ser 20, 22, 25, 84, 113, 115, 156, Thr90, Tyr17, 43, 111, 130, 162). However, such sites have a high probability of occurrence (protein kinase C, casein kinase II, and tyrosine kinase sites) and a site prediction may not necessarily indicate a genuine modification.

[0128] The primary sequence of OmCI shows 58% identity to tick Salivary Gland Proteins 2 and 3 (TSGP2 and 3) of the soft tick Ornithodorus savignyi (Mans et al, 2001), and 49% identity to moubatin from Ornithodorus moubata (Waxman and Connolly, 1993). All the cysteine residues, and therefore presumably the disulphide bridging pattern, are conserved in these four proteins (FIG. 5). The alignment shows that OmCI has two obvious short amino acid insertions: SESD at the amino terminus and PD about two-thirds of the way through the sequence of the mature peptide (FIG. 5). The primary sequence does not have a significant match with any other any other sequences in public databases including the anti-complement protein of I. scapularis (Valenzuela et al., 2000). Moubatin, and TSGP2 and 3 are believed to be members of the lipocalin family of beta barrel forming proteins that include the histamine binding protein family of tick specific proteins (Paesen et al., 2000).

Expression and Purification of Recombinant (r) OmCI

[0129] The 6 positive yeast clones assayed exhibited variable levels of OmCI expression (FIGS. 6a and b). In all cases where expression was detected, inhibitory activity continually increased through to the final assay point on day 5. Approximately 90% of the expressed protein was in the supernatant (FIG. 6b). Clone 13.1 appeared to give the highest expression levels and was used for subsequent expression studies. Following PEG precipitation and two chromatography steps partially purified active rOmCI is present in heavily glycosylated (FIG. 7a, fractions 9, 10 and 11) and unglycosylated forms (FIG. 7a, fractions 12 and 13). The glycosylated form was shown to correspond to the unglycosylated form by treatment with PNGaseF (FIG. 7b). Glycosylated and unglycosylated or deglycosylated rOmCi and native OmCI are equally active in CH50 assays (data not shown). The final yield of rOmCi was approximately 0.3 g/ml of media.

Mechanism of Action of OmCI

[0130] OmCI inhibits both complement pathways. However while the classical pathway can be entirely inhibited, even excess OmCI inhibits lysis of red blood cells by the alternative pathway by no more than 80% (FIG. 8).

[0131] OmCI does not prevent incorporation of C8 and C9 into preformed C5b-7 or C5b-8, respectively (FIG. 9). Nor does it affect the rate of C3 cleavage to yield C3a by either the classical or the alternative pathways (FIG. 10). OmCI does prevent production of C5a from C5 by both pathways (FIG. 11). Excess pure C5, but not C3 out-competes, the OmCI inhibitor in the classical haemolytic assay (FIG. 12). OmCI does not prevent decomplementation of sera by CVF (data not shown). Nor does it prevent C5a production by the CVF C3/C5 convertase (CVFBb) (FIG. 11).

Thermostability and pH Stability of Native OmCI

[0132] Boiling OmCI for up to 9 minutes did not have a significant affect on the inhibitory activity of the protein, although by 27 minutes inhibitory activity had decreased (FIG. 13). Native OmCI was unaffected by exposure to alkaline buffers up to pH 11 (FIG. 14). Exposure to buffer of pH 4.5 markedly decreased the inhibitory activity of OmCI (FIG. 14). Silver stained gels showed that this was not simply due to precipitation of OmCI at this pH (data not shown).

Detection of C5 Binding to OmCI

[0133] Western blotting with I.sup.125 labelled C3 and C5 indicates that OmCI binds directly to C5 but not to the related protein C3 (FIG. 15).

[0134] Additional evidence for a direct interaction between OmCI and C5 was obtained by gel filtration chromatography. An apparent mass shift in a proportion of the I.sup.125 labelled nOmCI was observed in the presence of purified C5 but not C3 (FIG. 16a). A similar mass shift was evident in the presence of NHS and C3 depleted sera but not C5 depleted sera (FIG. 16b). The mass shift was maintained in the presence of 1M NaCl but not 2M NaCl indicating a strong electrostatic interaction between the inhibitor and C5 (data not shown).

DISCUSSION

Relationship to Other Proteins and to Known Complement Inhibitors

[0135] OmCI is most closely related to tick salivary gland proteins 2 and 3 (TSGP2 and 3) of the soft tick O. savignyi (Mans et al., 2001) and the platelet aggregation inhibitor moubatin (Waxman and Connolly, 1993). It has not been shown, or suggested, that any of these three proteins (FIG. 5) inhibit complement. The two small amino acid insertions present in OmCI but not in the closely related proteins (FIG. 5) are obvious sites to focus on in future mutagenesis studies to define complement binding sites in OmCI.

[0136] TSGP2 and 3 have 95% amino acid identity and have been proposed to have roles in the granule biogenesis of tick salivary glands (Mans et al, 2001). TSGP2 is toxic to mice; TSGP3 is not (Mans et al, 2002). OmCI is highly unlikely to be a toxin since O. moubata is non-toxic (Astigarraga et al., 1997) whereas O. savignyi causes sand tampan toxicoses in a wide range of mammals (Mans et al, 2002). Furthermore, inoculation of guinea pigs with 100 g of purified native OmCI, in the process of raising antisera, caused no obvious pathophysiological effects (personal observation).

[0137] OmCI is probably a member of the lipocalin family of proteins that include the histamine binding protein family of tick specific proteins (Paesen et al., 2000). Lipocalins predominantly bind small, hydrophobic, extracellular ligands within their beta-barrel structures. However, the histamine binding protein of the tick Rhipicephalus appendiculatus has significant structural differences from normal lipocalins that enable it to bind hydrophilic molecules (Paesen et al., 1999; Paesen et al., 2000). It is not yet known whether OmCI binds any small ligands.

[0138] The primary sequence of OmCI has no detectable similarity to complement control protein (CCP) domains (multiple c.60 amino acid repeats) which form many of the bodies own complement inhibitors including factor H, C4BP, CR1, CR2, MCP and DAF). Nor is it similar to any other known complement inhibitors in public databases including Isac, the salivary complement alternative pathway inhibitor protein of Ixodes scapularis (Valenzuela et al., 2000). It is also unrelated to the N-terminal sequence of O. moubata antigen 20A1 (Baranda et al., 2000) which was proposed to be the factor responsible for the potent complement inhibition previously observed in the SGE's of O. moubata and O. erraticus (Astigarraga et al., 1997).

Mechanism of Complement Inhibition

[0139] Both glycosylated and deglycosylated rOmCI expressed in yeast are as potent as the native protein purified from SGE. C-terminal histidine tagged OmCI expressed in insect cells is not as potent (data not shown). OmCI inhibits both the classical and alternative pathways of complement activation of both humans and guinea pigs and presumably other mammals as well. This property should prove useful in defining precisely how OmCI works, and will be invaluable in the development of animal models of complement mediated diseases where the species specificity of present C5 inhibitors have hampered in vivo studies using rodents (Link et al., 1999).

[0140] OmCI does not inhibit either the classical (C4bC2a) or the alternative (C3bBb) C3 convertase since it has no effect on the rate of C3 cleavage (FIG. 10). OmCI does prevent production of C5a from C5 (FIG. 11). Since excess C5 out-competes the OmCI inhibitor (FIG. 12) functional classical (C4bC2aC3b) and alternative (C3b.sup.2Bb) C5 convertases must be formed in the presence of the tick inhibitor. OmCI is unlikely to be a direct serine protease inhibitor of the convertase catalytic components C2a and Bb or it would prevent C3a as well as C5a production. The inhibitor does not prevent C5a production by the CVF C3/C5 convertase (CVFBb) (FIG. 11) which suggests OmCI does not bind C5 and block the C5a cleavage site. The latter finding does not exclude the possibility that OmCI binds to a site on C5 that prevents binding to the normal serum C5 convertases but not to the CVF convertase (Sandoval et al., 2000).

[0141] Two independent lines of evidence suggest OmCI activity is mediated through direct binding to C5 (FIG. 15 and FIG. 16).

[0142] Although OmCI inhibits both complement pathways, even with excess inhibitor the alternative pathway is inhibited by at most 80% (FIG. 8). This is explicable in terms of the different C5 convertases used by the classical (C4bC2aC3b) and alternative (C3b.sup.2Bb) pathways, but the mechanism remains to be explored.

[0143] In summary, OmCI probably either binds C5 and prevents it interacting with the C5 convertases or binds the C5 convertases and C5 and prevents C5 cleavage. Presently we have no compelling evidence supporting one possibility over the other.

Thermostability and pH Stability of Native OmCI

[0144] OmCI is thermostable but activity begins to be lost after being boiled for 27 minutes. OmCI appears to be sensitive to acid and insensitive to alkali. Both prolonged boiling and exposure to acid probably induce conformational changes that inactivate the protein.

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