The ligand-binding function of integrin adhesion receptors depends on divalent cations. A mutant αIIbβ3 integrin (platelet gpIIb/IIIa) that lacks ligand recognition shows immunologic evidence ofa perturbed interaction with divalent cations. This was found to be caused by a G→T mutation that resulted in an Asp119→Tyr119 substitution in the β3 subunit. This residue is proximal to bound ligand and is in a conserved region among integrins that are enriched in oxygenated residues. The spacing ofthese residues aligns with the calcium-binding residues in EF hand proteins, suggesting interaction with receptor-bound divalent cation as a mechanism of ligand binding common to all integrins.
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