HUMAN KININOGENS INTERACT WITH M-PROTEIN, A BACTERIAL SURFACE PROTEINAND VIRULENCE DETERMINANT

Steptococcus pyogenes, the most significant streptococcal species in c linical 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 prote in, 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, where as 6 M protein-negative mutant strains showed no affinity. M protein o f most serotypes bind fibrinogen, and among the 55 strains tested, bin ding of kininogens was closely correlated to fibrinogen binding (r = 0 .88, P < 0.0001). Western blotting, slot binding and enzyme immunoassa y experiments demonstrated that M proteins isolated from S. pyogenes o f three different M protein serotypes (M1, M6 and M46) bound kininogen s. The affinity between kininogens and M1 protein was determined to be 5 x 10(7) M(-1) and less than or equal to 10(6) M(-1) for high molecu lar weight (H-kininogen) and low molecular weight kininogen, respectiv ely. The kininogen binding site was tentatively mapped to the N-termin al portion of M1 protein, and this site does not overlap the specific and separate binding sites for albumin, IgG and fibrinogen. using mono clonal antibodies to, and synthetic peptides of, the kininogen sequenc e, the major M protein-binding site(s) was mapped to the C-terminal po rtion of the H-kininogen light chain. We anticipate that the kininogen -M protein interaction contributes to the host-parasite relationship i n S. pyogenes infections.