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Human kininogens interact with M protein, a bacterial surface protein and virulence determinant
A B Ben Nasr1, H Herwald, W Müller-Esterl
1Department of Medical and Physiological Chemistry, Lund University, Sweden.
Abstract:
Streptococcus pyogenes, the most significant streptococcal species in clinical medicine, expresses surface proteins with affinity for several human plasma proteins. Here we report that kininogens, the precursors to the vasoactive kinins, bind to the surface of S. pyogenes. M protein, a surface molecule and a major virulence factor-in these bacteria, occurs in > 80 different serotypes. Among 49 strains of S. pyogenes, all of different M serotypes, 41 bound radiolabelled kininogens, whereas 6 M protein-negative mutant strains showed no affinity. M protein of most serotypes bind fibrinogen, and among the 55 strains tested, binding of kininogens was closely correlated to fibrinogen binding (r = 0.88, P < 0.0001). Western blotting, slot binding and enzyme immunoassay experiments demonstrated that M proteins isolated from S. pyogenes of three different M protein serotypes (M1, M6 and M46) bound kininogens. The affinity between kininogens and M1 protein was determined to be 5 x 10(7) M-1 and < or = 10(6) M-1 for high molecular weight (H-kininogen) and low molecular weight kininogen, respectively. The kininogen binding site was tentatively mapped to the N-terminal portion of M1 protein, and this site does not overlap the specific and separate binding sites for albumin, IgG and fibrinogen using monoclonal antibodies to, and synthetic peptides of, the kininogen sequence, the major M protein-binding site(s) was mapped to the C-terminal portion of the H-kininogen light chain. We anticipate that the kininogen-M protein interaction contributes to the host-parasite relationship in S. pyogenes infections.
Insights
Streptococcus pyogenes binds kininogens, precursors to vasoactive kinins, via its M protein. This interaction, closely correlated with fibrinogen binding, may influence S. pyogenes infections.
Area of Science:
- Microbiology
- Molecular Biology
- Biochemistry
Background:
- Streptococcus pyogenes is a significant human pathogen expressing surface proteins that bind host plasma proteins.
- M protein is a major virulence factor of S. pyogenes, with over 80 serotypes identified.
- Previous studies show M protein's affinity for various plasma proteins like fibrinogen and albumin.
Purpose of the Study:
- To investigate the binding of kininogens to Streptococcus pyogenes.
- To determine if M protein mediates the interaction between S. pyogenes and kininogens.
- To map the binding sites involved in the kininogen-M protein interaction.
Main Methods:
- Screening of 49 S. pyogenes strains with different M serotypes for kininogen binding.
- Utilizing M protein-negative mutant strains to confirm M protein's role.
- Employing Western blotting, slot binding, and enzyme immunoassays with isolated M proteins.
- Characterizing binding affinities and mapping interaction sites using monoclonal antibodies and synthetic peptides.
Main Results:
- 41 out of 49 S. pyogenes strains tested showed affinity for radiolabeled kininogens.
- M protein-negative mutants did not bind kininogens, confirming M protein's essential role.
- Kininogen binding strongly correlated with fibrinogen binding (r = 0.88).
- M proteins from serotypes M1, M6, and M46 bound kininogens, with specific affinities determined for M1 protein.
- The kininogen binding site on M1 protein was mapped to the N-terminal region, while the M protein binding site on kininogen was mapped to the C-terminal light chain.
Conclusions:
- Streptococcus pyogenes M protein directly binds kininogens.
- The interaction between kininogens and M protein is significant and may play a role in S. pyogenes pathogenesis.
- Understanding this interaction provides insights into the host-parasite relationship during infection.