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Localization of the third heparin-binding site in the human complement regulator factor H1
Rebecca J Ormsby1, T Sakari Jokiranta, Thomas G Duthy
1Department of Microbiology and Infectious Diseases, Flinders Medical Centre, University of South Australia, Bedford Park, Adelaide, Australia. rebecca.ormsby@flinders.edu.au
Molecular Immunology
|November 3, 2005
Summary
Complement factor H (fH) regulates complement activation. Researchers identified a third heparin-binding site in SCR 9, enhancing understanding of fH
Area of Science:
- Immunology
- Biochemistry
Background:
- Complement factor H (fH) is crucial for regulating the alternative complement pathway.
- fH prevents complement-mediated damage to host cells by interacting with polyanions like glycosaminoglycans (GAGs).
- fH contains 20 short consensus repeats (SCRs), with known heparin-binding sites in SCR 7 and SCR 20.
Purpose of the Study:
- To precisely locate the third heparin-binding domain of complement factor H.
- To investigate the avidity and specificity of fH's heparin-binding sites.
Main Methods:
- Utilized extensive recombinant fH fragments.
- Employed heparin affinity chromatography to isolate and analyze binding domains.
- Tested binding of fH fragments to endothelial cells.
Main Results:
- Localized the third heparin-binding domain to SCR 9.
- Demonstrated that SCR 7 and SCR 9 together exhibit higher heparin affinity than SCR 7 alone.
- Confirmed SCR 9's ability to bind endothelial cells, indicating physiological relevance.
- Observed distinct GAG specificities among the three heparin-binding sites.
Conclusions:
- The third heparin-binding site of fH is located in SCR 9.
- Multiple heparin-binding sites can interact simultaneously, increasing binding avidity.
- Individual binding domains may possess specific GAG recognition functions, contributing to host cell protection.