Covalent structure of single-stranded fibrin oligomers cross-linked by FXIIIa

FXIIIa-mediated isopeptide γ–γ bonds are produced between γ polypeptide chains of adjacent monomeric fibrin. Despite the use of the different methodological approaches there are apparently conflicting ideas regarding the orientation of γ–γ bonds. To identify the orientation of these bonds a novel approach has been applied. It was based on self-assembly of soluble cross-linked fibrin protofibrils ongoing in the urea solution of moderate concentrations followed by dissociation of protofibrils in the conditions of increasing urea concentration. The oligomers were composed of monomeric desA fibrin molecules created by cleavage of the fibrinopeptides A from fibrinogen molecules with thrombin-like enzyme, reptilase. The results of elastic and dynamic light scattering coupled with analytical ultracentrifugation indicated an emergence of the double-stranded rod-like fibrin protofibrils. For the first time, the protofibrils are proved to exhibit an ability to dissociate under increasing urea concentration to yield single-stranded structures. Since no accumulation of α polymers has been found the covalent structure of soluble single-stranded fibrin oligomers is entirely brought about by γ–γ bonds. The results of this study provide an extra evidence to support the model of the longitudinal γ–γ bonds that form between the γ chains end-to-end within the same strand of a protofibril. • Cross-linked double-stranded fibrin oligomers are obtained in the urea environment. • Cross-linked oligomers dissociate under increasing urea concentration. • Single-stranded oligomers produced are ligated by γ–γ bonds only. • γ–γ dimers are proved to be formed longitudinally within the same fibrin strand.