EVIDENCE FOR A METHYL-ACCEPTING CHEMOTAXIS PROTEIN GENE (MCP1) THAT ENCODES A PUTATIVE SENSORY TRANSDUCER IN VIRULENT TREPONEMA-PALLIDUM

The clinical and histopathological manifestations of syphilis and the invasive behavior of Treponema pallidum in tissue culture systems refl ect the propensity for treponemes to migrate through skin, hematogenou sly disseminate, and invade targeted tissues. Treponemal motility is b elieved to be essential to this process and thereby an important facet of syphilis pathogenesis. By analogy with other bacterial pathogens, it is plausible that treponemal motility and tissue invasion are modul ated by sensory transduction events associated with chemotactic respon ses, Recent studies have demonstrated the existence in T. pallidum of accessory molecules typically associated with sensory transduction eve nts involving methyl-accepting chemotaxis proteins (MCPs), Intrinsic r adiolabeling of T. pallidum in vitro with L-[methyl-H-3] methionine re vealed one methylated treponemal polypeptide with an apparent molecula r mass of 64 kDa. A degenerate oligonucleotide probe corresponding to a highly conserved C-terminal domain within Bacillus subtilis and Esch erichia coil MCPs was used in Southern blotting of T. pallidum DNA to identify and subsequently clone a putative T. pallidum MCP gene (mcp1) . Computer analyses predicted a near-consensus promoter upstream of mc p1, and primer extension analysis employing T. pallidum RNA revealed a transcriptional initiation site. T. pallidum mcp1 encoded a 579-amino -acid (64.6-kDa) polypeptide which was highly homologous to at least 6 9 other known or putative sensory transducer proteins, with the highes t degrees of homology existing between the C terminus of mcp1 and the C-terminal (signaling) domains of the other bacterial MCPs. Other sali ent features of Mcp1 included (i) six potential membrane-spanning doma ins at the N terminus, (ii) two predicted alpha-helical coiled coil re gions containing at least three putative methylation sites, and (iii) homologies with two ligand-binding domains (LI-I and LI-2) of the E. c oil MCPs Trg and Tar. This study is the first to provide both metaboli c and genetic evidence for an MCP sensory transducer in T. pallidum, T he combined findings prompt key questions regarding the relationship(s ) among sensory transduction, regulation of endoflagellar rotation, an d chemotactic responses (in particular, the role of glucose) during vi rulence expression by T. pallidum.