Binding of the Cysteine Proteinases Papain and Cathepsin B-like to Coated Laminin: Use of Synthetic Peptides from Laminin and from the Laminin Binding Region of the β1Integrin Subunit to Characterize the Binding Site

Cysteine proteinases of the papain superfamily, i.e., papain and cathepsin B-like proteinase, were found to be able to bind to laminin-coated wells. When papain and cathepsin B-like proteinase were used, saturable binding curves were found. The characterization of the binding site was carried out using synthetic peptides which corresponded to the most relevant functional sites of laminin and an octapeptide from the laminin binding region of the β1integrin subunit. In binding experiments, the decapeptide RNIAEIIKDI and the pentapeptide YIGSR were able to displace papain and cathepsin B-like proteinase from coated laminin. Nevertheless, the integrin β1peptide DLYYLMDL was the most powerful in the same experimental system. From these results, the C-terminal region of this cross-shaped protein, i.e., the end of the long arm, and the region including the YIGSR sequence of the short arm of the β chain would be the cysteine proteinase binding site. This binding site is probably the result of the network organization of laminin which brings two regions, separated on a single laminin molecule, into proximity. In previous work, digestion of basement membranes has been found to be associated with the binding of cysteine proteinases to these supramolecular structures [N. Guinec, V. Dalet-Fumeron, and M. Pagano (1992)FEBS Lett.308, 305–308]. The present report demonstrates that laminin is the cysteine proteinase binding protein of basement membranes. This property of laminin could be associated with tumor invasion and other tissue remodeling processes linked to proteolysis of basement membranes and extracellular matrices.