Full-length and truncated forms of vitronectin provide insight into effects of proteolytic processing on function

A genetic polymorphism in the vitronectin allele directs the production of two distinct forms of the 459 amino acid glycoprotein. A methionine present at position 381 favors production of the single-chain form of vitronectin, while threonine at this position increases the susceptibility of vitronect in to cleavage just beyond its heparin-binding domain at residue 379. This reaction gives rise to a disulfide-bonded, two-chain form of vitronectin. I n order to investigate the functional significance of the vitronectin polym orphism, the baculovirus system has been used to express recombinant full-l ength vitronectin and a truncated form of the molecule that represents the 62-kDa fragment of two-chain vitronectin. Both forms of vitronectin bind an d neutralize heparin anticoagulant activity. The proteins also bind PAI-1 a nd stabilize its active conformation. These experiments suggest that the C- terminal 80 amino acids do not confer a functional difference in the two al lelic variants. Immunoassays and gel filtration experiments indicate that b oth full-length and truncated recombinant forms of vitronectin are multimer ic. Together with other reports from this laboratory, these results provide information regarding the primary binding sites for two vitronectin ligand s and further define regions that may be involved in multimerization of the protein. (C) 2001 Elsevier Science B.V. All rights reserved.