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Localization by site-directed mutagenesis of the site in human complement factor H that binds to Streptococcus
1Department of Biochemistry, The University of Texas Health Science Center, Tyler 75710-2003, USA.
Abstract:
M-protein receptors located on Streptococcus pyogenes cells are known to bind human plasma protein factor H. Human factor H is composed of 20 short consensus repeat (SCR) domains containing approximately 60 amino acids each. Factor H controls the activation of the alternative pathway of complement in plasma. We have scanned the entire human factor H molecule by site-directed deletion mutagenesis, expressed the recombinant proteins in insect cells using the baculovirus system, and measured the binding of different purified mutant proteins to three strains of S. pyogenes. These studies have revealed that recombinant factor H lacking SCR domains 6 to 10 does not bind to wild-type M+ S. pyogenes JRS4. Experiments performed with S. pyogenes JRS251, in which both C-repeat domains of M protein were deleted, demonstrated that all of the factor H mutant proteins bound weakly to these cells except those lacking the SCR region from domains 6 to 10. Neither human factor H nor any of the recombinant proteins bound to the M- strain JRS145. Our results indicate that the only binding site on human factor H that interacts with streptococcus M protein is located in SCR domains 6 to 10 of factor H and that regions of M protein outside the C-repeat domains are involved in binding factor H.
Insights
Streptococcus pyogenes M protein binds human factor H via specific domains. Researchers identified that short consensus repeat domains 6 to 10 of factor H are crucial for this interaction.
Area of Science:
- Microbiology
- Immunology
- Molecular Biology
Background:
- Streptococcus pyogenes M protein mediates binding to human factor H.
- Human factor H comprises 20 short consensus repeat (SCR) domains and regulates complement activation.
- Understanding this interaction is key to pathogen evasion strategies.
Purpose of the Study:
- To pinpoint the specific domains of human factor H responsible for binding to Streptococcus pyogenes M protein.
- To investigate the role of M protein's C-repeat domains in factor H binding.
Main Methods:
- Site-directed deletion mutagenesis of human factor H.
- Expression of recombinant factor H mutants using the baculovirus system in insect cells.
- Assessment of mutant factor H binding to different strains of S. pyogenes.
Main Results:
- Recombinant factor H lacking SCR domains 6 to 10 failed to bind wild-type M+ S. pyogenes.
- Factor H mutants lacking SCR domains 6 to 10 showed no binding to M- S. pyogenes.
- Binding was observed for other factor H mutants to M+ S. pyogenes, suggesting involvement of regions outside C-repeat domains in M protein.
Conclusions:
- The binding site for Streptococcus pyogenes M protein on human factor H is localized to SCR domains 6 to 10.
- Regions of M protein outside the C-repeat domains are involved in the interaction with factor H.