Biophysical characterization of fibrinogen Caracas I with an Aalpha-chain truncation at Aalpha-466 Ser: identification of the mutation and biophysical characterization of properties of clots from plasma and purified fibrinogen.

Fibrinogen Caracas I is a dysfibrinogenemia with a mild bleeding tendency; a novel nonsense mutation, in the gene coding the Aalpha-chain, identified in this study as G4731T, giving rise to a new stop codon at Aalpha-Glu 467. Fibrinogen from two family members, the mother and sister of the propositus, both heterozygous for the mutation were studied, analyzing clots made from both plasma and purified fibrinogen. Clot structure and properties were characterized by turbidity, permeation, scanning electron microscopy and rheological studies. Permeation through Caracas I plasma clots was decreased, consistent with the decreased final turbidity. As shown by scanning electron microscopy, plasma clots from the patients were composed of very thin fibers, with increased fibrin density and reduced pore size. Viscoelastic measurements revealed that fibrinogen Caracas I plasma clots were much stiffer and less subject to compaction. These results demonstrate a key role of the carboxyl-terminal alpha chains of fibrin in lateral aggregation during polymerization and reinforce the utility of studying plasma clots. It is important to point out that the biophysical studies with fibrinogen purified by two different methods yielded contradictory results, which can be accounted for by selective purification of certain molecular species as seen by two-dimensional electrophoresis.