Biochemical and biological properties of the binding of human fibrinogen to M protein in group A streptococci.
Fibrinogen is known to bind to group A streptococci and precipitate with extracts containing streptococcal M protein. We have previously shown that the binding of fibrinogen to M-positive streptococci prevents opsonization by complement and protects that organism from phagocytosis in nonimmune blood. In the present study, we used 3H-labeled fibrinogen, a highly purified peptide fragment of type 24 M protein (pep M24), and anti-pep M sera to show that fibrinogen binds to M-positive streptococci with high affinity (dissociation constants, 1 to 5 nM); occupation of the high-affinity binding sites suffices to protect the organism from phagocytosis; proteolytic treatments that remove M protein from streptococcal cells abolish binding; binding is competitively inhibited by anti-pep M sera; pep M24 precipitates fibrinogen; and binding to type 24 cells is inhibited by pep M24. We conclude that M protein is the cell surface structure principally responsible for binding fibrinogen on the surface of M-positive streptococci and that this binding contributes to the known antiopsonic property of M proteins.
D000942:Antigens, Bacterial; D001425:Bacterial Outer Membrane Proteins; D001426:Bacterial Proteins / Q000378:metabolism*; D001665:Binding Sites; D002352:Carrier Proteins; D011232:Chemical Precipitation; D005340:Fibrinogen / Q000378:metabolism*; D006801:Humans; D010447:Peptide Hydrolases / Q000494:pharmacology; D010587:Phagocytosis; D013297:Streptococcus pyogenes / Q000378:metabolism*; D014316:Tritium
D000942:Antigens, Bacterial; D001425:Bacterial Outer Membrane Proteins; D001426:Bacterial Proteins; D002352:Carrier Proteins; C014689:streptococcal M protein; D014316:Tritium; D005340:Fibrinogen; D010447:Peptide Hydrolases