Interaction between collagen and the alpha(2) I-domain of integrin alpha(2)beta(1). Critical role of conserved residues in the metal ion-dependent adhesion site (MIDAS) region.

A docking model of the alpha(2) I-domain and collagen has been proposed based on their crystal structures (Emsley, J., King, S., Bergelson, J., and Liddington, R. C. (1997) J. Biol. Chem. 272, 28512-28517). In this model, several amino acid residues in the I-domain make direct contact with collagen (Asn-154, Asp-219, Leu-220, Glu-256, His-258, Tyr-285, Asn-289, Leu-291, Asn-295, and Lys-298), and the protruding C-helix of alpha(2) (residues 284-288) determines ligand specificity. Because most of the proposed critical residues are not conserved, different I-domains are predicted to bind to collagen differently. We found that deleting the entire C-helix or mutating the predicted critical residues had no effect on collagen binding to whole alpha(2)beta(1), with the exception that mutating Asn-154, Asp-219, and His-258 had a moderate effect. We performed further studies and found that mutating the conserved surface-exposed residues in the metal ion-dependent adhesion site (MIDAS) (Tyr-157 and Gln-215) significantly blocks collagen binding. We have revised the docking model based on the mutagenesis data. In the revised model, conserved Tyr-157 makes contact with collagen in addition to the previously proposed Asn-154, Asp-219, His-258, and Tyr-285 residues. These results suggest that the collagen-binding I-domains (e.g. alpha(1), alpha(2), and alpha(10)) bind to collagen in a similar fashion.