A synthetic peptide derived from the carboxy terminus of the laminin A chain represents a binding site for the α₃β₁ integrin

The purpose of this study was to identify the binding site(s) within laminin for the α₃β₁ integrin-receptor. It has been previously shown, using proteolytic fragments and anti-laminin antibodies, that the region in laminin for α₃β₁ integrin binding is localized to the carboxy-terminal region at the end of the long arm (Gehlsen, K. R., E. Engvall, K. Dickerson, W. S. Argraves, and E. Ruoslahti. 1989. J. Biol. Chem. 264:19034-19038; Tomaselli, K. J., D. E. Hall, L. T. Reichardt, L. A. Flier, K. R. Gehlsen, D. C. Turner, and S. Carbonetto. 1990. Neuron. 5:651-662). Using synthetic peptides, we have identified an amino acid sequence within the carboxy- terminal region of the laminin A chain that is recognized by the α₃β₁ integrin. The amino acid sequence represented by the synthetic peptide GD-6 (KQNCLSSRASFRGCVRNLRLSR residues numbered 3011 to 3032) of the globular domain of the murine A chain supports cell attachment and inhibits cell adhesion to laminin-coated surfaces. By affinity chromatography, peptide GD- 6-Sepharose specifically bound solubilized α₃β₁ from extracts of surface- iodinated cells in a cation-dependent manner, while it did not bind other integrins. In addition, exogenous peptide GD-6 specifically eluted bound α₃β₁ from laminin-Sepharose columns but did not elute the α₃β₁ integrin from a fibronectin-Sepharose column. Using integrin subunit-specific monoclonal antibodies, only those antibodies against the α₃ and β₁ subunits inhibited cell adhesion to peptide GD-6-coated surfaces. Finally, a polyclonal antibody made against peptide GD-6 reacted specifically with both murine and human laminin and significantly inhibited cell adhesion to laminin-coated surfaces but not those coated with other matrix proteins. These results identify the laminin A chain amino acid sequence of peptide GD- 6 as representing a binding site in laminin for the α₃β₁ integrin.