Identification of opcA gene in Neisseria polysaccharea: interspecies diversity of Opc protein family.

The gene encoding the outer membrane adhesin/invasin protein OpcA was previously described in the genomes of two pathogenic Neisseria species, N. meningitidis (Nm) and N. gonorrhoeae (Ng). In order to understand the presence or absence of opcA in nonpathogenic Neisseria species, 13 strains of N. polysaccharea (Np), four strains of N. lactamica, three strains of N. subflava and nine strains of other species were examined by DNA hybridization, polymerase chain reaction (PCR) and nucleotide sequencing. The opcA gene was found in two Np strains (85322 and 89357). The Np-opcA gene is a novel member of this gene family with 93% homology to Ng-opcA. Comparison of opcA-surrounding regions among eight Neisseria strains revealed five types of genetic organization at the opcA locus in Neisseria, which result from insertion or deletion of genetic elements at the upstream region of opcA. Comparison of the deduced peptide sequences from two Np strains, two representative Ng strains, two representative Nm strains and 13 Nm sequence variants demonstrates interspecies diversity of the OpcA protein family with conserved transmembrane regions and species-specific polymorphism at the surface-exposed loops and periplasmic turns. Reverse transcription-PCR analysis and Northern blotting showed that Np-opcA was transcribable. From an alignment of the Np-OpcA and Ng-OpcA sequences against the three-dimensional crystal structure of Nm-OpcA we conclude that there is no obvious structural reason why these proteins would not be able to form stable, folded, outer membrane proteins. The data presented here provide additional information for understanding the distribution, variation and expression of opcA in Neisseria.