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Fibronectin mediates Treponema pallidum cytadherence through recognition of fibronectin cell-binding domain
Abstract:
The specificity of the interaction between Treponema pallidum and fibronectin was demonstrated. Treatment of host cells with only antifibronectin sera and not anticollagen or antilaminin sera, inhibited treponemal cytadsorption. Incubation of fibronectin-coated coverslips with monoclonal antibody to the cell-binding domain of fibronectin reduced treponemal attachment to the same extent as antifibronectin serum. Both iodinated fibronectin and iodinated cell-binding domain bound to T. pallidum in a saturable manner. Specificity of the T. pallidum association with the cell-binding domain was the most effective inhibitor of the binding of either radioiodinated cell-binding domain or fibronectin to T. pallidum. Scatchard analysis gave Kd on the order of 10(-7) M for both cell-binding domain and fibronectin binding to T. pallidum, consistent with the high affinity interaction of these organisms with host cell surfaces. Finally, the same level of attachment of treponemes was achieved on coverslips coated with cell-binding domain as that observed for organisms incubated with fibronectin, indicating that the cell-binding domain polypeptide is functionally identical to fibronectin in mediating T. pallidum adherence.
Insights
Treponema pallidum specifically binds to fibronectin, a key host cell protein. This interaction is mediated by fibronectin's cell-binding domain, crucial for treponemal adherence.
Area of Science:
- Microbiology
- Cell Biology
- Infectious Diseases
Background:
- Treponema pallidum is the causative agent of syphilis.
- Host cell surface proteins play a role in pathogen adherence.
- Fibronectin is a major extracellular matrix protein involved in cell adhesion.
Purpose of the Study:
- To investigate the specific interaction between Treponema pallidum and fibronectin.
- To identify the domain of fibronectin responsible for mediating T. pallidum attachment.
- To characterize the binding affinity and kinetics of this interaction.
Main Methods:
- Inhibition assays using antifibronectin, anticollagen, and antilaminin sera.
- Monoclonal antibody blocking of fibronectin's cell-binding domain.
- Binding studies with radioiodinated fibronectin and its cell-binding domain.
- Scatchard analysis to determine binding constants (Kd).
Main Results:
- Antifibronectin sera, but not others, inhibited T. pallidum cytadsorption.
- Monoclonal antibodies to the fibronectin cell-binding domain significantly reduced treponemal attachment.
- Both fibronectin and its cell-binding domain bound to T. pallidum in a saturable, high-affinity manner (Kd ~10(-7) M).
- The cell-binding domain alone effectively mediated T. pallidum adherence, similar to intact fibronectin.
Conclusions:
- Treponema pallidum specifically interacts with fibronectin via its cell-binding domain.
- This interaction is a high-affinity process crucial for T. pallidum adherence to host cells.
- The cell-binding domain of fibronectin is functionally sufficient for mediating treponemal attachment.