The C-terminal Region of Laminin β Chains Modulates the Integrin Binding Affinities of Laminins

Laminins are major cell-adhesive proteins in basement membranes that are capable of binding to integrins. Laminins consist of three chains (alpha, beta, and gamma), in which three laminin globular modules in the alpha chain and the Glu residue in the C-terminal tail of the gamma chain have been shown to be prerequisites for binding to integrins. However, it remains unknown whether any part of the beta chain is involved in laminin-integrin interactions. We compared the binding affinities of pairs of laminin isoforms containing the beta 1 or beta 2 chain toward a panel of laminin-binding integrins, and we found that beta 2 chain-containing laminins (beta 2-laminins) bound more avidly to alpha 3 beta 1 and alpha 7X2 beta 1 integrins than beta 1 chain-containing laminins (beta 1-laminins), whereas alpha 6 beta 1, alpha 6 beta 4, and alpha 7X1 beta 1 integrins did not show any preference toward beta 2-laminins. Because alpha 3 beta 1 contains the X2-type variable region in the alpha 3 subunit and alpha 6 beta 1 and alpha 6 beta 4 contain the X1-type region in the alpha 6 subunit, we hypothesized that only integrins containing the X2-type region were capable of discriminating between beta 1-laminins and beta 2-laminins. In support of this possibility, a putative X2-type variant of alpha 6 beta 1 was produced and found to bind preferentially to beta 2-laminins. Production of a series of swap mutants between the beta 1 and beta 2 chains revealed that the C-terminal 20 amino acids in the coiled-coil domain were responsible for the enhanced integrin binding by beta 2-laminins. Taken together, the results provide evidence that the C-terminal region of beta chains is involved in laminin recognition by integrins and modulates the binding affinities of laminins toward X2-type integrins.