Conservation ofmsp, the Gene Encoding the Major Outer Membrane Protein of OralTreponemaspp.

Themajorsurfaceprotein(Msp)of Treponema denticolahasbeenimplicatedasamediatoroftheinteraction between the spirochete and the gingival epithelium in periodontal diseases. Previous studies showed that the Msp of T. denticolaATCC 35405 had porin activity, depolarized epithelial cell membranes, bound to extracel- lular matrix components of epithelial cells, and formed a regular hexagonal surface array in the treponemal outer membrane. The gene encoding Msp in ATCC 35405 was recently cloned, sequenced, and expressed in Escherichia coli (J. C. Fenno, K.-H. Muller, and B. C. McBride, J. Bacteriol. 178:2489-2496, 1996). In the present study, we identified genes encoding Msp-like proteins in several oral spirochetes. A prominent heat- modifiable Msp-like protein having an apparent molecular mass of between 43 and 64 kDa was present in all oral spirochete strains tested. Antibodies raised against the ATCC 35405 Msp reacted strongly with the Msp proteins of T. denticolaATCC 35404 and T. vincentii, reacted very weakly with the Msp protein of T. denticola ATCC 33520, and did not react with T. denticolaOTK, T. socranskii, and T. pectinovorum. The msploci of the T. denticolastrains and T. vincentiiwere identified in analyses using PCR with oligonucleotide primers derived from the DNA sequenceflanking mspin ATCC 35405. Southern blot analysis showed at least three groups of related mspDNAsequences.ComparisonofDNAsequencesofthe5*and3*endsofthe mspgenesshowedhigh sequence homology in the flanking regions and signal peptide coding regions, while the homologies between regions encoding the mature peptide were as low as 50%. The entire mspDNA sequences of T. denticolaATCC 33520 and OTK were determined, and the deduced Msp amino acid sequences were compared to the sequence of the previously reported Msp of ATCC 35405. The results show that the msp locus is conserved in oral treponemes but that there are significant differences between the mature Msp peptides of different strains. Further studies of the antigenic domains, functional domains, and physical structures of Msp proteins, based on these results, will enhance understanding of the role of Msp in the cytopathology associated with oral spirochetes. Periodontal diseases are characterized by mixed bacterial infections associated with progressive destruction of the tissue surrounding and supporting the teeth. Oral spirochetes of the genus Treponema are associated with both acute and chronic periodontal diseases and are frequently found in high numbers at diseased sites in both adult periodontitis (21, 25) and early- onset juvenile periodontitis (26). Identification of specific treponemes as periodontopathogens is complicated by the in- abilitytocultivatemostoralspirochetesinvitro(3).Ofthefive