The vitronectin binding area of plasminogen activator inhibitor-1, mapped by mutagenesis and protection against an inactivating organochemical ligand.

A distinguishing feature of serpins is their ability to undergo a conformational change consisting in insertion of the reactive centre loop (RCL) into beta-sheet A. In the serpin plasminogen activator inhibitor-1 (PAI-1), RCL movements are regulated by vitronectin, having a previously poorly defined binding site lateral to PAI-1's beta-sheet A. Using a novel strategy, based on identification of amino acid residues necessary for vitronectin protection of PAI-1 against inactivation by 4,4'-dianilino-1,1'-bisnaphthyl-5,5'-disulfonic acid, we have defined a vitronectin binding surface spanning 10 residues between alpha-helix F, beta-strand 2A, and alpha-helix E. Our results contribute to elucidating the unique serpin conformational change.