Related Experiment Videos
M protein of the group A Streptococcus binds to the seventh short consensus repeat of human complement factor H
T K Blackmore1, V A Fischetti, T A Sadlon
1Department of Microbiology and Infectious Diseases, Flinders University of South Australia and Flinders Medical Centre, Bedford Park. Tim.Blackmore@flinders.edu.au
Abstract:
Streptococcus pyogenes evades complement by binding the complement-regulatory protein factor H (fH) via the central conserved C-repeat region of M protein. However, the corresponding binding region within fH has not previously been precisely localized. fH is composed of 20 conserved modules called short consensus repeats (SCRs), each of which contains approximately 60 amino acids. A series of fH truncated and deletion mutants were prepared, and their interaction with M6 protein was examined. The M protein binding site was initially localized to SCRs 6 to 15 as demonstrated by ligand dot blotting, chemical cross-linking, and enzyme-linked immunosorbent assay. SCR 7 was then shown to contain the M protein binding site, as a construct consisting of the first seven SCRs bound M protein but a construct containing the first six SCRs did not bind. In addition, deletion of SCR 7 from full-length fH abolished binding to M protein. SCR 7 is known to contain a heparin binding domain, and binding of fH to M6 protein was almost totally inhibited in the presence of 400 U of heparin per ml. These results localize the M6 protein binding site of fH to SCR 7 and indicate that it is in close proximity to the heparin binding site.
Insights
Streptococcus pyogenes uses M protein to bind factor H (fH), evading complement. Researchers precisely located this binding site on fH to SCR 7, near its heparin-binding domain.
Area of Science:
- Microbiology
- Immunology
- Biochemistry
Background:
- Streptococcus pyogenes employs M protein to bind complement-regulatory factor H (fH), a mechanism for immune evasion.
- Factor H comprises 20 short consensus repeat (SCR) modules, but the specific M protein binding site within fH was uncharacterized.
Purpose of the Study:
- To precisely map the M protein binding site on factor H.
- To investigate the relationship between the M protein and heparin binding sites on factor H.
Main Methods:
- Utilized truncated and deletion mutants of factor H.
- Employed ligand dot blotting, chemical cross-linking, and ELISA to assess M protein binding.
- Investigated the effect of heparin on fH-M protein interaction.
Main Results:
- The M protein binding site on factor H was narrowed down to SCRs 6-15.
- Further analysis pinpointed SCR 7 as the specific M protein binding site.
- Binding of M6 protein to fH was significantly inhibited by heparin, indicating proximity to the heparin-binding domain.
Conclusions:
- The M6 protein binding site on factor H is localized to SCR 7.
- This binding site is closely associated with the heparin-binding domain of factor H.
- Understanding this interaction offers insights into complement evasion strategies of Streptococcus pyogenes.