Certain high molecular weight heparin chains have high affinity for vitronectin

Vitronectin is a 70-kDa protein that is found in both the extracellular mat rix as well as serum. Vitronectin is one of the few proteins that regulates both the complement and the coagulation systems. Heparin is known to bind to vitronectin. Review of the literature reveals apparently conflicting out comes of the interaction of heparin, vitronectin, and the complement system . Previous studies demonstrated that heparin diminishes vitronectin inhibit ion of complement activity. Numerous studies have also demonstrated that he parin exerts a net inhibitory effect on complement. We used two dimensional affinity resolution electrophoresis (2DARE) to examine this apparent parad ox. 2DARE allowed simultaneous determination of binding affinity of heparin for vitronectin as well, as the M-r of the heparin species. In the 2DARE e xperiment, the interaction of heparin with vitronectin caused retardation o f the movement of the heparin through the tube gel in the first dimension. The degree of the retardation of movement was used to calculate the approxi mate K-d of that interaction. The heparin from the tube gel was then subjec ted to a second dimension electrophoresis to determine the M-r of the hepar in, 2DARE analysis of the interaction of heparin with vitronectin clearly d emonstrated that a sub-population of heparin chains with M-r > 8000 bound v itronectin with high affinity whereas most high M-r chains and all lower M- r chains showed little to no affinity for vitronectin. Our findings are con sistent with the hypothesis that a unique binding domain exists in certain heparin chains for vitronectin. (C) 2001 Academic Press.