Selective Binding of Collagen Subtypes by Integrin α1I, α2I, and α10I Domains

Abstract

Four integrins, namely α1β1, α2β1 α10β1and α11β1, form a special subclass of cell adhesion receptors. They are all collagen receptors, and they recognize their ligands with an inserted domain (I domain) in their α subunit. We have produced the human integrin α10I domain as a recombinant protein to reveal its ligand binding specificity. In general, α10I did recognize collagen types I-VI and laminin-1 in a Mg2+ -dependent manner, whereas its binding to tenascin was only slightly better than to albumin. When α10I was tested together with the α1I and α2I domains, all three I domains seemed to have their own collagen binding preferences. The integrin α2I domain bound much better to fibrillar collagens (I-III) than to basement membrane type IV collagen or to beaded filament-forming type VI collagen. Integrin α1I had the opposite binding pattern. The integrin α10I domain was similar to the α1I domain in that it bound very well to collagen types IV and VI. Based on the previously published atomic structures of the α1I and α2I domains, we modeled the structure of the α10I domain. The comparison of the three I domains revealed similarities and differences that could potentially explain their functional differences. Mutations were introduced into the αI domains, and their binding to types I, IV, and VI collagen was tested. In the α2I domain, Asp-219 is one of the amino acids previously suggested to interact directly with type I collagen. The corresponding amino acid in both the α1I and α10I domains is oppositely charged (Arg-218). The mutation D219R in the α2I domain changed the ligand binding pattern to resemble that of the α1I and α10I domains and, vice versa, the R218D mutation in the α1I and α10I domains created an α2I domain-like ligand binding pattern. Thus, all three collagen receptors appear to differ in their ability to recognize distinct collagen subtypes. The relatively small structural differences on their collagen binding surfaces may explain the functional specifics.