THE EFFECT OF SUBSTITUTED LAMININ A CHAIN-DERIVED PEPTIDES ON THE CONFORMATION AND ACTIVATION KINETICS OF PLASMINOGEN

Conversion of the zymogen plasminogen (Pg) to the active enzyme plasmi n is catalyzed by proteinases such as tissue-type plasminogen activato r (t-PA). Interaction of Pg with small ligands such as lysine or macro molecular ligands such as fibrin induces a dramatic conformational cha nge in the zymogen which enhances its efficacy as a t-PA substrate, th ereby increasing catalytic efficiency of the activation reaction. We h ave previously demonstrated that a synthetic peptide derived from amin o acids 2091-2108 of the laminin A chain (designated LamA(2091-2108)) can significantly enhance t-PA-catalyzed Pg activation. To probe the m echanism of this stimulatory reaction, we have determined the effect o f substituted LamA(2091-2108) derivatives on Pg activation by t-PA. Su bstitution of charged residues in LamA(2091-2108) With neutral amino a cids decreases the k(cat)/K-m observed in the presence of native LamA( 2091-2108). Furthermore, fluorescence-quenching experiments demonstrat e that whereas LamA(2091-2108) alters the solvent accessibility of Pg Trp residues, charge-substituted peptides have little effect on Pg con formation. These data suggest that LamA(2091-2108) stimulates Pg activ ation by inducing a conformational change in the zymogen similar to th at observed upon binding of other ligands such as lysine and fibrin. ( C) 1994 Academic Press, Inc.