Ligand-binding specificities of laminin-binding integrins: A comprehensive survey of laminin–integrin interactions using recombinant α3β1, α6β1, α7β1 and α6β4 integrins

The interactions of cells with basement membranes are primarily mediated via the engagement of laminins by a group of integrin family proteins, including integrins α3β1, α6β1, α7β1 and α6β4. To explore the ligand-binding specificities of these laminin-binding integrins, we produced these integrins, including two α7β1 splice variants (α7X1β1 and α7X2β1), as soluble recombinant proteins and determined their binding specificities and affinities toward a panel of purified laminin isoforms containing distinct α chains. Among the five laminin-binding integrins investigated, α3β1 and α6β4 exhibited a clear specificity for laminin-332 (α3β3γ2) and laminin-511 (α5β1γ1)/521 (α5β2γ1), while integrin α6β1 showed a broad specificity, binding to all laminin isoforms with a preference for laminin-111 (α1β1γ1), laminin-332 and laminin-511/521. The two α7β1 variants were distinct from α3β1, α6β1 and α6β4 in that they did not bind to laminin-332. α7X1β1 bound to all laminins, except laminin-332, with a preference for laminin-211 (α2β1γ1)/221 (α2β2γ1) and laminin-511/521, while α7X2β1 bound preferentially to laminin-111 and laminin-211/221. Laminin-511/521 was the most preferred ligand for all the laminin-binding integrins, except for α7X2β1, whereas laminin-411 was the poorest ligand, capable of binding to α6β1 and α7X1β1 with only modest binding affinities. These comprehensive analyses of the interactions between laminin-binding integrins and a panel of laminins clearly demonstrate that the isoforms of both integrins and laminins differ in their binding specificities and affinities, and provide a molecular basis for better understanding of the adhesive interactions of cells with basement membranes of defined laminin compositions.