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Molecular characterization of receptor binding proteins and immunogens of virulent Treponema pallidum
Abstract:
Receptor binding proteins of Treponema pallidum were identified by incubation of [35S]methionine-labeled, soluble T. pallidum preparations with formaldehyde-fixed HEp-2 cells. Three major treponemal proteins (bands 1--3) that avidly bound to the eucaryotic cell surface were detected by sodium dodecylsulfate-polyacrylamide gel electrophoresis and fluorography. Brief trypsin treatment of HEp-2 cells before formaldehyde fixation reduced the extent of the interaction of these treponemal macromolecules, which implicated receptor-mediated attachment mechanisms. The presence of unlabeled T. pallidum preparations directly competed with radiolabeled T. pallidum samples for the available HEp-2 cells, which suggested a limiting number of membrane binding sites. Samples of unlabeled avirulent Reiter treponeme did not compete. T. Pallidum immunogens were examined by radioimmunoprecipitation with human and rabbit syphilitic sera. Of interest were the similarities and extent of the humoral response represented by the detection of antigen-antibody complexes against numberous treponemal proteins, including bands 1--3. T. pallidum portein band 1 appeared to be the major antigenic stimulus. Formation of antigen-antibody complexes between 35S-labeled T. pallidum proteins and human syphilitic sera was prevented by unlabeled T. pallidum but not by T. phagedenis preparations, which demonstrated specificity of the reaction. Gel profiles of radioimmunoprecipitation assays using radiolabeled T. pallidum antigens and human syphilitic and yaws sera delineated both the similarities and differences in the humoral response to these two spirochetes. The latter suggested both overlapping and distinguishing antigenic properties between T. pallidum and T. pertenue. Detection in yaws sera of specific antibody against T. pallidum protein bands 1--3 further incriminates the role of these three treponemal proteins as virulence determinants.
Insights
Researchers identified three key Treponema pallidum proteins that bind to host cells, suggesting a receptor-mediated attachment mechanism. These proteins are also major targets of the immune response in syphilis and yaws, indicating their role in virulence.
Area of Science:
- Microbiology
- Immunology
- Cell Biology
Background:
- Treponema pallidum is the causative agent of syphilis.
- Understanding the interaction between T. pallidum and host cells is crucial for developing effective diagnostics and therapeutics.
- Previous studies have suggested T. pallidum utilizes specific surface proteins for host cell attachment.
Purpose of the Study:
- To identify and characterize Treponema pallidum receptor binding proteins.
- To investigate the role of these proteins in host cell attachment and immune response.
- To explore the antigenic similarities and differences between T. pallidum and T. pertenue.
Main Methods:
- Incubation of radiolabeled T. pallidum with HEp-2 cells.
- Sodium dodecylsulfate-polyacrylamide gel electrophoresis (SDS-PAGE) and fluorography to detect bound proteins.
- Trypsin treatment of HEp-2 cells to assess attachment mechanisms.
- Competition assays with unlabeled T. pallidum and Reiter treponeme.
- Radioimmunoprecipitation assays using human and rabbit syphilitic sera, and yaws sera.
Main Results:
- Three major T. pallidum proteins (bands 1-3) were identified that bind to HEp-2 cells.
- Binding was reduced by trypsin treatment, indicating receptor-mediated attachment.
- Unlabeled T. pallidum competed for binding sites, suggesting limited membrane receptors.
- These three proteins were major immunogens, eliciting antibody responses in syphilitic and yaws sera.
- Protein band 1 was identified as a major antigenic stimulus.
- Humoral responses showed similarities and differences between T. pallidum and T. pertenue, with antibodies against bands 1-3 detected in yaws sera.
Conclusions:
- T. pallidum utilizes specific surface proteins (bands 1-3) for receptor-mediated attachment to host cells.
- These proteins are significant virulence determinants and major targets of the humoral immune response in syphilis and yaws.
- The findings suggest potential for these proteins in diagnostic and vaccine development.