Nanoscale Probing Reveals that Reduced Stiffness of Clots from Fibrinogen Lacking 42 N-Terminal Bβ-Chain Residues Is Due to the Formation of Abnormal Oligomers

Removal of B beta 1-42 from fibrinogen by Crotalus atrox venom results in a molecule lacking fibrinopeptide Band part of a thrombin binding site. We investigated the mechanism of polymerization of desB beta 1-42 fibrin. Fibrinogen trinodular structure was clearly observed using high resolution noncontact atomic force microscopy. E-regions were smaller in desB beta 1-42 than normal fibrinogen (1.2 nm +/- 0.3 vs. 1.5 nm +/- 0.2), whereas there were no differences between the D-regions (1.7 nm +/- 0.4 vs. 1.7 nm +/- 0.3). Polymerization rate for desB beta 1-42 was slower than normal, resulting in clots with thinner fibers. Differences in oligomers were found, with predominantly lateral associations for desB beta 1-42 and longitudinal associations for normal fibrin. Clot elasticity as measured by magnetic tweezers showed a G' of similar to 1 Pa for desB beta 1-42 compared with similar to 8 Pa for normal fibrin. Spring constants of early stage desB beta 1-42 single fibers determined by atomic force microscopy were similar to 3 times less than normal fibers of comparable dimensions and development. We conclude that B beta 1-42 plays an important role in fibrin oligomer formation. Absence of B beta 1-42 influences oligomer structure, affects the structure and properties of the final clot, and markedly reduces stiffness of the whole clot as well as individual fibrin fibers.