CHLORAMINE T-INDUCED STRUCTURAL AND BIOCHEMICAL-CHANGES IN ECHISTATIN

Echistatin is a member of the disintegrin family of peptides and a pot ent inhibitor of platelet aggregation and cell adhesion. Echistatin bi nds to integrin alpha(v)beta(3) and alpha(IIb)beta(3) receptors with h igh affinity. Binding is mediated by an RGD-containing loop maintained in an appropriate conformation by disulfide bridges, In this study, w e hale compared the binding characteristics of echistatin iodinated by either lactoperoxidase or chloramine T method, We show that echistati n labeled by lactoperoxidase method binds to integrin alpha(v)beta(3) receptor with high affinity and in a non-dissociable manner very simil ar to native echistatin, In contrast, chloramine T-labeled echistatin can rapidly dissociate from the receptor. We demonstrate that chlorami ne T reaction results in the addition of an extra oxygen to the methio nine residue adjacent to the RGD motif in echistatin. Modeling studies and molecular dynamic simulation studies show that the extra oxygen a tom on the methionine residue can form hydrogen bonds with the glycine and aspartic acid residues of the RGD motif, These structural changes in echistatin help explain the changes in the binding characteristics of the molecule following chloramine T reaction. (C) 1998 Federation of European Biochemical Societies.