EVIDENCE FOR A SPECIFIC INTERACTION OF VITRONECTIN WITH ARGININE - EFFECTS OF REDUCING AGENTS ON THE EXPRESSION OF FUNCTIONAL DOMAINS AND IMMUNOEPITOPES

Vitronectin (Vn) circulates in plasma primarily in the native, monomer ic form, whereas platelet-associated Vn is conformationally altered an d multimeric. Here, we report that denatured Vn specifically binds to L-Arg, whereas the L-Arg binding site is cryptic in the native form of Vn. In addition, combined treatment of disulfide-linked Vn multimers with L-Arg, urea, and reducing agent results in the formation of dispe rse oligomers with reduced expression of denaturation-sensitive epitop es. These results suggest that L-Arg modulates the partitioning betwee n monomeric and multimeric Vn species and that L-Arg affinity chromato graphy can be employed to test for exposure of conformationally sensit ive binding sites in Vn. The effects of denaturation on the exposure o f conformationally sensitive epitopes in the N-terminus of Vn is contr oversial. Treatment of Vn with reducing agents abolished type 1 plasmi nogen activator inhibitor and antibody binding to the highly disulfide -linked N-terminal somatomedin B domain (amino acids 1 to 51), whereas epitopes located in the connecting region/first hemopexin-like repeat (amino acids 52 to 239) and the glycosaminoglycan binding domain (ami no acids 343-379) were not affected. These observations indicate that appropriate disulfide-linkage of the N-terminal somatomedin B domain i s required for ligand binding and that published differences on the ef fects of denaturation on the expression of binding sites are probably due to the use of reducing agents in the denaturation process.