Recombinant BβArg14His fibrinogen implies participation of N-terminus of Bβ chain in desA fibrin polymerization

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Abstract
We synthesized BβArg14His fibrinogen with histidine substituted for arginine at the Bβ thrombin-cleavage site. This substitution led to a 300-fold decrease in the rate of thrombin-catalyzed fibrinopeptide B (FpB, Bβ 1-14) release, whereas the rate of FpA release was normal with either thrombin or the FpA-specific enzyme, batroxobin. Both thrombin- and batroxobincatalyzed polymerization of BβArg14His fibrinogen were significantly impaired, with a longer lag time, slower rate of lateral aggregation, and decreased final turbidity. Moreover, desA monomer polymerization was similarly impaired, demonstrating that the histidine substitution itself, and not the lack of FpB cleavage, caused the abnormal polymerization of BβArg14His fibrin. Scanning electron microscopy showed BβArg14His fibrin fibers were thinner than normal (BβArg14His, approximately 70 nm; normal, approximately 100 nm; P < .0001), as expected from the decreased final turbidity. We conclude that the N-terminus of the Bβ chain is involved in the lateral aggregation of normal desAprotofibrils and that the Arg→His substitution disrupts these interactions in BβArg14His fibrinogen. (Blood. 2003;102:2466-2471)