Biophysical Mechanisms of Von Willebrand Factor-Collagen Interactions

Abstract

Von Willebrand factor (VWF) is a multimeric plasma glycoprotein that mediates platelet adhesion onto bleeding blood vessels by binding to both sub-endothelial collagen and platelets. VWF-collagen interactions are capable of resisting the substantial force imposed by blood flow or captured platelets, yet their biomechanical properties have not been identified. The mechanical strength of the VWF-collagen anchorage relative to VWF-platelet adhesion remains unclear. This work examines the mechanical unbinding between A3, the collagen-binding domain of VWF, and human type I collagen, one of the major constituents of the subendothelium. Single-molecule force measurements of A3-collagen interactions were conducted via atomic force microscopy. Depending on the loading rates, the unbinding forces between recombinant A3 and collagen or between VWF multimers and collagen ranged from 50 to 105 pN. When using multimeric VWF constructs bearing the loss-of-function, type 2M mutations in the A3 domain, either no or decreased unbinding forces were observed. The data is consistent with the bleeding phenotypes of these mutations observed in patients with von Willebrand disease (VWD). Moreover, A3-collagen interactions are only stronger than A1-platelet interactions when the pulling force is greater than 15 pN. Together, the data suggest that the A3-collagen interaction is suitable for mediating platelet adhesion under high shear flow and that VWD A3 mutations impair the mechanical properties of the interaction.