title: TP0326, a Treponema pallidum β-barrel assembly machinery A (BamA) orthologue and rare outer membrane protein.
abstract: Definitive identification of Treponema pallidum rare outer membrane proteins (OMPs) has long eluded researchers. TP0326, the sole protein in T. pallidum with sequence homology to a Gram-negative OMP, belongs to the BamA family of proteins essential for OM biogenesis. Structural modelling predicted that five polypeptide transport-associated (POTRA) domains comprise the N-terminus of TP0326, while the C-terminus forms an 18-stranded amphipathic β-barrel. Circular dichroism, heat modifiability by SDS-PAGE, Triton X-114 phase partitioning and liposome incorporation supported these topological predictions and confirmed that the β-barrel is responsible for the native protein's amphiphilicity. Expression analyses revealed that native TP0326 is expressed at low abundance, while a protease-surface accessibility assay confirmed surface exposure. Size-exclusion chromatography and blue native polyacrylamide gel electrophoresis revealed a modular Bam complex in T. pallidum larger than that of Escherichia coli. Non-orthologous ancillary factors and self-association of TP0326 via its β-barrel may both contribute to the Bam complex. T. pallidum-infected rabbits mount a vigorous antibody response to both POTRA and β-barrel portions of TP0326, whereas humans with secondary syphilis respond predominantly to POTRA. The syphilis spirochaete appears to have devised a stratagem for harnessing the Bam pathway while satisfying its need to limit surface antigenicity.
authors.affiliation: Department of Medicine, University of Connecticut Health Center, Farmington, CT 06040, USA.
authors.forename: Daniel C
authors.initials: DC
authors.lastname: Desrosiers
authors.forename: Arvind
authors.initials: A
authors.lastname: Anand
authors.forename: Amit
authors.initials: A
authors.lastname: Luthra
authors.forename: Star M
authors.initials: SM
authors.lastname: Dunham-Ems
authors.forename: Morgan
authors.initials: M
authors.lastname: LeDoyt
authors.forename: Michael A D
authors.initials: MA
authors.lastname: Cummings
authors.forename: Azad
authors.initials: A
authors.lastname: Eshghi
authors.forename: Caroline E
authors.initials: CE
authors.lastname: Cameron
authors.forename: Adriana R
authors.initials: AR
authors.lastname: Cruz
authors.forename: Juan C
authors.initials: JC
authors.lastname: Salazar
authors.forename: Melissa J
authors.initials: MJ
authors.lastname: Caimano
authors.forename: Justin D
authors.initials: JD
authors.lastname: Radolf
mesh_terms: D000595:Amino Acid Sequence; D001425:Bacterial Outer Membrane Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D002462:Cell Membrane / Q000378:metabolism / Q000382:microbiology*; D006801:Humans; D008969:Molecular Sequence Data; D017433:Protein Structure, Secondary; D017434:Protein Structure, Tertiary; D016415:Sequence Alignment; D013587:Syphilis / Q000378:metabolism / Q000382:microbiology*; D014210:Treponema pallidum / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*
chemical_list: D001425:Bacterial Outer Membrane Proteins