Subunit Flexibility of Multimeric von Willebrand Factor/Factor VIII Complexes.

Abstract

Von Willebrand factor (VWF) is a plasma glycoprotein that participates in platelet adhesion and aggregation and serves as a carrier for blood coagulation factor VIII (fVIII). Plasma VWF consists of a population of multimers that range in molecular weight from ∼ 0.55 MDa to greater than 10 MDa. The VWF multimer consists of a variable number of concatenated disulfide-linked ∼275 kDa subunits. We fractionated plasma-derived human VWF/fVIII complexes by size-exclusion chromatography at a pH of 7.4 and subjected them to analysis by sodium dodecyl sulfate agarose gel electrophoresis, sedimentation velocity analytical ultracentrifugation (SV AUC), dynamic light scattering (DLS), and multi-angle light scattering (MALS). Weight-average molecular weights, Mw, were independently measured by MALS and by application of the Svedberg equation to SV AUC and DLS measurements. Estimates of the Mark–Houwink–Kuhn–Sakurada exponents , αs, and αD describing the functional relationship between the z-average radius of gyration, , weight-average sedimentation coefficient, sw, z-average diffusion coefficient, Dz, and Mw were consistent with a random coil conformation of the VWF multimer. Ratios of to the z-average hydrodynamic radius, , estimated by DLS, were calculated across an Mw range from 2 to 5 MDa. When compared to values calculated for a semi-flexible, wormlike chain, these ratios were consistent with a contour length over 1000-fold greater than the persistence length. These results indicate a high degree of flexibility between domains of the VWF subunit.