Pathobiology of Human Fibrinogen. Binding site for Staphylococci on Aα and Bβ chains of Fibrinogen Molecule

The ability of human fibrinogen to interact with some staphylococci to cause a non-enzymatic clumping reaction has been used to detect fibrinogen and its derivates in blood and body fluids. We studied localization of the binding site for staphylococci on human fibrinogen using ¹²⁵I-fibrinogen after reduction and alkylation of polypeptide chains, CNBr-treatment, and limited plasmin digestion. This combined approach revealed that the staphylococci-binding site is located on Aα and B β chains involving C-terminal portion but not N-terminal disulfide knot, γ chain has no binding site for staphylococci. Abnormal fibrinogens with defects in the N-terminal portion interacted normally with staphylococci. The degree of binding paralleled the extent of clumping reaction between staphylococci and ¹²⁵I-fibrinogen or its plasminderived fragments. However, monomeric Scarboxymethyl Aα and B β chains showed a high degree of binding without concomitant clumping suggesting requirement for dimeric form of polypeptide chains for clumping. Conclusion: Aα and Bβ chains but not γ chain have homologous regions in terms of staphylococci-binding site on C-terminal portion responsible for clumping reaction. Thus, staphylococci can be used to measure abnormal fibrinogens with defects in the N-terminal region.

(Supported by NIH Grants and VA.)

 

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