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The outer membrane of Treponema pallidum: biological significance and biochemical properties
Abstract:
Rabbits infected intravenously with Treponema pallidum were not markedly febrile, and the pyrogenicity of treponeme preparations administered intravenously to rabbits was negligible. The antibiotic polymyxin B did not induce any ultrastructural changes on the treponemal surface and was not lethal (immobilizing) for T. pallidum, which was, however, highly susceptible to detergents such as SDS. Extraction of treponemes with Triton X-100 removed the outer membrane (despite the presence of Mg2+) as shown by electron microscopy, and solubilized a limited number of proteins detectable by SDS-PAGE, including a dominant antigen (47 kDal) demonstrated by immunoblotting. None of the proteins were heat-modifiable. Periodic acid-silver staining of polyacrylamide gels for carbohydrate together with protease K digestion did not demonstrate major carbohydrate components in whole treponemes, or in the Triton-soluble fraction. Surface iodination of intact treponemes revealed very little surface exposure of treponemal proteins, although a protein which co-migrated with host albumin was labelled and appeared to be associated with the treponemal surface. Many treponemal proteins were, however, labelled when iodination was done in the presence of Triton. These observations, indicate that the outer membrane of T. pallidum differs significantly from those of many Gram-negative pathogens.
Insights
Treponema pallidum outer membrane composition differs from other Gram-negative pathogens. Detergents like Triton X-100 removed the outer membrane, revealing limited proteins and a dominant 47 kDa antigen.
Area of Science:
- Microbiology
- Immunology
- Pathogen Biology
Background:
- Treponema pallidum is the causative agent of syphilis.
- Understanding the T. pallidum outer membrane is crucial for developing diagnostics and therapeutics.
- Previous studies suggest T. pallidum's unique characteristics compared to other Gram-negative bacteria.
Purpose of the Study:
- To investigate the biochemical and ultrastructural properties of the Treponema pallidum outer membrane.
- To identify major antigens and carbohydrate components of T. pallidum.
- To compare the T. pallidum outer membrane with those of other Gram-negative pathogens.
Main Methods:
- Intravenous infection of rabbits with T. pallidum.
- Treatment of treponemes with polymyxin B, SDS, and Triton X-100.
- Electron microscopy for ultrastructural analysis.
- SDS-PAGE and immunoblotting for protein analysis.
- Periodic acid-silver staining for carbohydrate detection.
- Surface iodination of treponemes with and without Triton.
Main Results:
- T. pallidum infections in rabbits were not significantly febrile; treponeme preparations had negligible pyrogenicity.
- Polymyxin B did not alter treponeme surface ultrastructure or exhibit lethality, while SDS showed high susceptibility.
- Triton X-100 extraction removed the outer membrane, solubilizing limited proteins, including a dominant 47 kDa antigen.
- No significant heat-modifiable proteins or major carbohydrate components were detected.
- Surface iodination revealed minimal protein exposure, with a host albumin-like protein associated with the surface. Triton-assisted iodination labelled numerous proteins.
Conclusions:
- The outer membrane of T. pallidum possesses distinct biochemical properties compared to many Gram-negative pathogens.
- T. pallidum exhibits limited surface protein exposure and a unique response to detergents.
- Further research into T. pallidum's outer membrane may yield novel targets for syphilis intervention.