Antigenic differences among Campylobacter fetus S-layer proteins

Abstract

Sodium dodecyl sulfate-polyacrylamide gel electrophoresis of S-layer proteins extracted from Campylobacter fetus strains by using acid glycine buffer showed that the predominant S-layer proteins of different strains had subunit molecular weights in the range of 90,000 to 140,000. Electron microscopy revealed oblique S-layer lattices with a spacing of approximately 5.6 nm (y = 750) on wild-type strains VC1, VC119, VC202, and VC203. Three variants of C. fetus VC119 producing a predominant S-layer subunit protein of different molecular weight (Mr) from that of the parent were also examined. Each variant produced an oblique lattice morphologically indistinguishable from that of the parent. Amino-terminal sequence analysis showed that the S-layer proteins of the VC119 parent and variants were identical up to residue 18 and that this sequence differed from but was related to the first 16 N-terminal residues shared by the S-layer proteins of the three other wild-type C. fetus isolates. Western immunoblot analysis with an antiserum prepared to the VC119 protein and an antiserum prepared to C. fetus 84-40 LP (Z. Pei, R. T. Ellison, R. V. Lewis, and M. J. Blaser, J. Biol.Chem. 263:6416-6420, 1988) showed that strains of C. fetus were capable of producing S-layer proteins with at least four different antigenic specificities. Immunoelectron microscopy with antiserum to the VC119 S-layer protein showed that C. fetus cultures contained cells with immunoreactive oblique S-layer lattices as well as ceUs with oblique S-layer lattices which did not bind antibody. This suggests that C. fetus S-layer proteins undergo antigenic variation. Thermal denaturation experiments indicated that the antigenicity conferred by the surface-exposed C. fetus S-layer epitopes was unusually resistant to heat, and the thermal stability appeared to be due to the highly organized lattice structure of the S layer. Protease digestion of purified VC119 S-layer protein revealed a trypsin-, chymotrypsin-, and endoproteinase Glu-C-resistant domain with an apparent Mr of 110,000, which carried the majority of the epitopes of the S-layer protein, and a small enzyme-sensitive domain. The trypsin-and chymotrypsin-resistant polypeptides shared an overlapping sequence which differed from the N-terminal sequence of the intact S-layer protein.

Reattachment of surface array proteins to Campylobacter fetus cells

“…Previous work has shown that S-layer proteins from type A strains all share the same amino terminus (31). However, S-layer proteins from a group of other C. fetus strains share another amino-terminal sequence (14,15). S-layer protein molecules from four of these strains (Table 1) were purified and used in the reattachment assay.…”

“…The mechanism by which the cell wall accommodates S-layer protein molecules larger than their presently expressed S-layer protein is unclear. Nevertheless, such a phenomenon was expected since C. fetus strains are able to shift S-layer protein size, and because the surface layer varies antigenically through changes of S-layer protein molecular weight (14,18,31,44). However, when we also tested a variety of divalent cations with different radii in reattachment assays, all worked similarly well.…”

“…C. fetus strains may shift the size of the predominant S-layer protein produced, which results in antigenic shift, although the mechanism is presently unknown (31,44). Nine different S-layer protein molecules have been purified and characterized (14,15,31), and two different aminoterminal amino acid sequences have been observed, but the biological significance of this variation has not been defined (14,15,29). C. fetus may lose its surface layer (becoming an S-mutant without significant change in other bacterial components) during sequential passage on artificial medium (7,26), a phenomenon also observed in Bacillus thuringiensis (24).…”

Isolation and comparison of the paracrystalline surface layer proteins of freshwater caulobacters

“…salmonicida (8). In a similar analysis of Campylobacterfetus, there were significant differences in the S-layer proteins of closely related strains and the suggestion that some form of antigenic variation occurred (11). Two strains of Aquaspirillum serpens were examined by peptide mapping and immunological cross-reaction; there is apparently a degree of similarity between the S-layer proteins (unpub-lished studies cited in reference 23).…”

Western Blot Analysis of the IgG-Antibody Response to Acid- Glycine-Extracted Antigens from Campylobacter fetus subsp. fetus and C. jejuni in Naturally Infected Sheep

“…These results indicate that the antibodies in sera from apparently healthy sheep could be acquired during a past C. fetus infection and sheep aborting recently due to C. fetus infection could have developed a substantial systemic antibody response directed against antigens with high molecular weight. Dubreuil et al (1990b) reported that the acid dissociable protein with low molecular weight, e.g. 31 kDa protein, appeared to be an antigenic determinant that is common to the thermophilic campylobacter strains, but not in C. fetus subsp.…”