A comparative analysis of pilin genes from pathogenic and nonpathogenic Neisseria species

Pathogenic Neisseria species elaborate type IV pili, which are considered important for virulence. In this study, we examined pilin-encoding expression loci (pilE) in nonpathogenic Neisseria species. PCR based screening detected homology to a conserved N-terminal region of pilE in 12 of 15 Neisseria species, including all human commensal isolates. The three species failing to display homology were isolated from nonhuman sources. We have also characterized complete pilE loci from the human commensal species N. lactamica and N. cinerea. As anticipated, the predicted protein sequences from these species display features typical of all type IV pilins. In addition, these commensal pilins possess two highly conserved regions, SV2 and CYS2, which are shared among all neisserial pilins. However, a comparative analysis of pilE loci from pathogenic and nonpathogenic Neisseria species reveals two distinct structural groups, one composed of the pilin genes from N. lactamica, N. cinerea, and the class II pilin-producing subset of N. meningitidis isolates, the other of gonococcal and meningococcal class I pilin-encoding genes. Since both class I and class II pilin-producing meningococci can act as pathogens, structural relationships among neisserial pilin genes do not obviously reflect either species membership or ability to cause human disease.