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 Bβ1-42 from fibrinogen by Crotalus atrox venom results in a molecule lacking fibrinopeptide B and part of a thrombin binding site. We investigated the mechanism of polymerization of desBβ1-42 fibrin. Fibrinogen trinodular structure was clearly observed using high resolution noncontact atomic force microscopy. E-regions were smaller in desBβ1-42 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 desBβ1-42 was slower than normal, resulting in clots with thinner fibers. Differences in oligomers were found, with predominantly lateral associations for desBβ1-42 and longitudinal associations for normal fibrin. Clot elasticity as measured by magnetic tweezers showed a G′ of ∼1 Pa for desBβ1-42 compared with ∼8 Pa for normal fibrin. Spring constants of early stage desBβ1-42 single fibers determined by atomic force microscopy were ∼3 times less than normal fibers of comparable dimensions and development. We conclude that Bβ1-42 plays an important role in fibrin oligomer formation. Absence of Bβ1-42 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. © 2009 by the Biophysical society.