Sequence Polymorphism, Predicted Secondary Structures, and Surface-Exposed Conformational Epitopes of Campylobacter Major Outer Membrane Protein

The major outer membrane protein (MOMP), a putative porin and a multifunction surface protein ofCampylobacter jejuni , may play an important role in the adaptation of the organism to various host environments. To begin to dissect the biological functions and antigenic features of this protein, the gene (designatedcmp ) encoding MOMP was identified and characterized from 22 strains ofC. jejuni and one strain ofC. coli . It was shown that the single-copycmp locus encoded a protein with characteristics of bacterial outer membrane proteins. Prediction from deduced amino acid sequences suggested that each MOMP subunit consisted of 18 β-strands connected by short periplasmic turns and long irregular external loops. Alignment of the amino acid sequences of MOMP from different strains indicated that there were seven localized variable regions dispersed among highly conserved sequences. The variable regions were located in the putative external loop structures, while the predicted β-strands were formed by conserved sequences. The sequence homology ofcmp appeared to reflect the phylogenetic proximity ofC. jejuni strains, since strains with identicalcmp sequences had indistinguishable or closely related macrorestriction fragment patterns. Using recombinant MOMP and antibodies recognizing linear or conformational epitopes of the protein, it was demonstrated that the surface-exposed epitopes of MOMP were predominantly conformational in nature. These findings are instrumental in the design of MOMP-based diagnostic tools and vaccines.