Critical role of the carbohydrate moiety in human von Willebrand factor protein for interactions with type I collagen.

The ability of von Willebrand factor protein (vWF) to agglutinate platelets with ristocetin depends upon the presence of its highest molecular weight multimers (HMWM) and its intact carbohydrate structure. Previously we demonstrated that the HMWM are preferentially adsorbed to purified fibrillar type I collagen. The role of the carbohydrate structure of vWF in this function has not been established. In these studies complete desialylation (greater than 95%) of the intact protein by neuraminidase did not interfere with the normal adsorption of vWF activity to type I collagen. In contrast, modification of the penultimate galactose of the desialylated protein with galactose oxidase or beta-galactosidase markedly reduced adsorption of vWF activity by collagen. Subsequent reduction of the oxidized desialylated protein with potassium borohydride completely regenerated the normal adsorption of vWF activity by collagen. Enzymatic modification of the penultimate galactose moiety of vWF resulted in a loss of the HMWM, as observed following SDS-glyoxyl agarose electrophoresis. This was in contrast to desialylated vWF, which appeared intact structurally and which predictably lost its HMWM upon exposure to collagen in a manner similar to native vWF. Therefore, the carbohydrate structure of vWF and, in particular, the penultimate galactose moiety, may be critical for vWF-collagen interactions and for the mediation of primary hemostasis.