Distinct Roles of beta 1 Metal Ion-dependent Adhesion Site (MIDAS), Adjacent to MIDAS (ADMIDAS), and Ligand-associated Metal-binding Site (LIMBS) Cation-binding Sites in Ligand Recognition by Integrin alpha 2 beta 1

作者：Valdramidou Dimitra; Humphries Martin J; Mould A Paul^*

来源：Journal of Biological Chemistry, 2008, 283(47): 32704-32714.

DOI：10.1074/jbc.M802066200

Integrin-ligand interactions are regulated in a complex manner by divalent cations, and previous studies have identified ligand-competent, stimulatory, and inhibitory cation-binding sites. In collagen-binding integrins, such as alpha 2 beta 1, ligand recognition takes place exclusively at the alpha subunit I domain. However, activation of the alpha I domain depends on its interaction with a structurally similar domain in the beta subunit known as the I-like or beta I domain. The top face of the beta I domain contains three cation-binding sites: the metal-ion dependent adhesion site (MIDAS), the ADMIDAS (adjacent to MIDAS), and LIMBS (ligand-associated metal-binding site). The role of these sites in controlling ligand binding to the alpha I domain has yet to be elucidated. Mutation of the MIDAS or LIMBS completely blocked collagen binding to alpha 2 beta 1; in contrast mutation of the ADMIDAS reduced ligand recognition but this effect could be overcome by the activating monoclonal antibody TS2/16. Hence, the MIDAS and LIMBS appear to be essential for the interaction between alpha I and beta I, whereas occupancy of the ADMIDAS has an allosteric effect on the conformation of beta I. An activating mutation in the alpha 2 I domain partially restored ligand binding to the MIDAS and LIMBS mutants. Analysis of the effects of Ca2+, Mg2+, and Mn2+ on ligand binding to these mutants showed that the MIDAS is a ligand-competent site through which Mn2+ stimulates ligand binding, whereas the LIMBS is a stimulatory Ca2+-binding site, occupancy of which increases the affinity of Mg2+ for the MIDAS.

• 出版日期2008-11-21