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From Constructs to Crystals – Towards Structure Determination of β-barrel Outer Membrane Proteins
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Published on: July 4, 2016

TP0326, a Treponema pallidum β-barrel assembly machinery A (BamA) orthologue and rare outer membrane protein

Daniel C Desrosiers1, Arvind Anand, Amit Luthra

  • 1Department of Medicine, University of Connecticut Health Center, Farmington, CT 06040, USA.

Molecular Microbiology
|April 15, 2011
PubMed

Insights

Treponema pallidum outer membrane protein TP0326, essential for cell wall biogenesis, was identified. Its structure and surface exposure were confirmed, revealing a unique bacterial complex and differential antibody responses in syphilis.

Area of Science:

  • Microbiology
  • Structural Biology
  • Immunology

Background:

  • Treponema pallidum outer membrane proteins (OMPs) are poorly characterized.
  • TP0326 is the only T. pallidum protein with homology to Gram-negative OMPs, belonging to the BamA family crucial for outer membrane biogenesis.

Purpose of the Study:

  • To definitively identify and characterize rare outer membrane proteins (OMPs) in Treponema pallidum.
  • To elucidate the structure, topology, and function of TP0326, a putative OMP.

Main Methods:

  • Structural modeling, circular dichroism, SDS-PAGE, Triton X-114 phase partitioning, liposome incorporation.
  • Expression analysis, protease-surface accessibility assays, size-exclusion chromatography, blue native PAGE.
  • Antibody response analysis in T. pallidum-infected rabbits and humans with secondary syphilis.

Main Results:

  • TP0326 possesses five N-terminal POTRA domains and an 18-stranded C-terminal β-barrel, confirmed by biophysical methods.
  • TP0326 is expressed at low levels, exposed on the bacterial surface, and forms a larger, modular Bam complex than in E. coli.
  • Rabbits show a strong antibody response to both POTRA and β-barrel domains of TP0326, while humans with secondary syphilis primarily respond to POTRA.

Conclusions:

  • TP0326 is a functional OMP involved in outer membrane biogenesis in T. pallidum.
  • The T. pallidum Bam complex is larger and potentially utilizes different ancillary factors compared to E. coli.
  • T. pallidum evades host immunity by limiting the surface antigenicity of TP0326, primarily eliciting a POTRA-specific antibody response in humans.

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