Recombinant fibrinogen Vlissingen/Frankfurt IV - The deletion of residues 319 and 320 from the gamma chain of fibrinogen alters calcium binding, fibrin polymerization, cross-linking and platelet aggregation

We synthesized a variant, recombinant fibrinogen modeled after the heterozy gous dysfibrinogen Vlissingen/Frankfurt IV, a deletion of two residues, gam ma Asn-319 and gamma Asp-320, located within the high affinity calcium-bind ing pocket. Turbidity studies showed no evidence of fibrin polymerization, although size exclusion chromatography, transmission electron microscopy, a nd dynamic light scattering studies showed small aggregates. These aggregat es did not resemble normal protofibrils nor did they clot. Fibrinopeptide A release was normal, whereas fibrinopeptide B release was delayed approxima tely 3-fold. Plasmin cleavage of this fibrinogen was not changed by the pre sence of calcium or Gly-Pro-Arg-Pro, indicating that both the calcium-bindi ng site and the "a" polymerization site were non-functional. We conclude th at the loss of normal polymerization was due to the lack of "A-a" interacti ons. Moreover, functions associated with the C-terminal end of the gamma ch ain, such as platelet aggregation and factor XIII cross-linking, were also disrupted, suggesting that this deletion of two residues affected the overa ll structure of the C-terminal domain of the gamma chain.