FIG 1 .
Domain architectures and membrane topologies of TprC (TP0117), TprD (TP0131), TprI (TP0620), and BamA (TP0326). (A) T. pallidum repeat (Tpr) subfamily I paralogs TprC (TP0117), TprD (TP0131), and TprI (TP0620) have identical domain architectures (35, 36). MOSPN and MOSPC correspond to conserved domains shared with the N and C termini of the major outer sheath protein (MOSP) of T. denticola, the parental Tpr ortholog, identified by the NCBI conserved domain database (CDD) server. Arrows indicate the regions that were subjected to PCR amplification for sequencing (see Table S3 for primers). The designation CVR (central variable region) denotes a sequence-variable stretch present in all Tpr orthologs (40, 77). BamA consists of a C-terminal β-barrel and five periplasmic polypeptide transport-associated (POTRA) domains (34, 37). Numbers refer to amino acid positions within the full-length proteins (signal peptides; denoted by “S,” included) from T. pallidum subsp. pallidum Nichols. (B) Membrane topologies. In Tpr orthologs and MOSP, the MOSPC domain forms the surface-exposed β-barrel (35, 36, 42). Immunofluorescence experiments in T. pallidum have confirmed the periplasmic location of MOSPN and the CVR of TprC/D (Nichols) and TprI (35, 36). Moreover, the periplasmic portions of TprC/D and TprI form extended structures, as determined by small-angle X-ray scattering analysis, that anchor the β-barrels to the peptidoglycan sacculus (35, 36). A homology model based on the solved structure of the Neisseria gonorrhoeae ortholog (38) predicts that the β-barrel of T. pallidum subsp. pallidum BamA contains 16 transmembrane β-strands and 8 extracellular loops (37). OM, outer membrane; PG, peptidoglycan; CM, cytoplasmic membrane; L4, BamA immunodominant extracellular loop 4.