Polymerization sites in the D-domain of human fibrin(ogen)

The present work deals with localization of previously unknown polymerization sites of the fibrin DD-fragment. D-dimer we obtained has a pronounced inhibitory effect on fibrin polymerization (IC50 = 0.06 microM). The inhibitory effect of the DD-fragment disappeared after reduction and carboxymethylation. However, polypeptide chains betaDD (Bbeta134-461) and gammagammaDD (gamma63-411)2 of the DD-fragment, isolated by preparative electrophoresis, displayed their inhibitory activity. For instance, the rates of fibrin protofibril lateral association were decreased twice in the presence of betaDD and gammagammaDD chains at their molar ratios to fibrin of 0.40 and 0.15, respectively. The IC50 values for betaDD and gammagammaDD were 0.24 and 0.10 microM, respectively. Highly specific inhibition of protofibril lateral association suggests that the protofibril lateral association sites are located in Bbeta134-461 and gamma63-411 regions of the fibrin D-domain. Our data confirm those reported by Doolittle et al. regarding the gamma-chain and a hypothesis about beta-chain of fibrin D-domain (Yang, Z., Mochalkin, I., and Doolittle, R. F. (2000) Biochemistry, 97, 14156-14161).