The requirement of the glutamic acid residue at the third position from the carboxyl termini of the laminin γ chains in integrin binding by laminins

Laminins are the major cell-adhesive proteins in the basement membrane, consisting of three subunits termed alpha, beta, and gamma. The putative binding site for integrins has been mapped to the G domain of the alpha chain, although trimerization with beta and gamma chains is necessary for the G domain to exert its integrin binding activity. The mechanism underlying the requirement of beta and gamma chains in integrin binding by laminins remains poorly understood. Here, we show that the C-terminal region of the gamma chain is involved in modulation of the integrin binding activity of laminins. We found that deletion of the C-terminal three but not two amino acids within the gamma 1 chain completely abrogated the integrin binding activity of laminin-511. Furthermore, substitution of Gln for Glu-1607, the amino acid residue at the third position from the C terminus of the gamma 1 chain, also abolished the integrin binding activity, underscoring the role of Glu-1607 in integrin binding by the laminin. We also found that the conserved Glu residue of the gamma 2 chain is necessary for integrin binding by laminin-332, suggesting that the same mechanism operates in the modulation of the integrin binding activity of laminins containing either gamma 1 or gamma 2 chains. However, the peptide segment modeled after the C-terminal region of gamma 1 chain was incapable of either binding to integrin or inhibiting integrin binding by laminin-511, making it unlikely that the Glu residue is directly recognized by integrin. These results, together, indicate a novel mechanism operating in ligand recognition by laminin binding integrins.