The ?-subunit regulates stability of the metal ion at the ligand-associated metal ion-binding site in ?3 integrins.

ABSTRACT: The aspartate in the prototypical integrin-binding motif Arg-Gly-Asp binds the integrin ?A domain of the ?-subunit through a divalent cation at the metal ion-dependent adhesion site (MIDAS). An auxiliary metal ion at a ligand-associated metal ion-binding site (LIMBS) stabilizes the metal ion at MIDAS. LIMBS contacts distinct residues in the ?-subunits of the two ?3 integrins ?IIb?3 and ?V?3, but a potential role of this interaction on stability of the metal ion at LIMBS in ?3 integrins has not been explored. Equilibrium molecular dynamics simulations of fully hydrated ?3 integrin ectodomains revealed strikingly different conformations of LIMBS in unliganded ?IIb?3 versus ?V?3, the result of stronger interactions of LIMBS with ?V, which reduce stability of the LIMBS metal ion in ?V?3. Replacing the ?IIb-LIMBS interface residue Phe(191) in ?IIb (equivalent to Trp(179) in ?V) with Trp strengthened this interface and destabilized the metal ion at LIMBS in ?IIb?3; a Trp(179) to Phe mutation in ?V produced the opposite but weaker effect. Consistently, an F191/W substitution in cellular ?IIb?3 and a W179/F substitution in ?V?3 reduced and increased, respectively, the apparent affinity of Mn(2+) to the integrin. These findings offer an explanation for the variable occupancy of the metal ion at LIMBS in ?V?3 structures in the absence of ligand and provide new insights into the mechanisms of integrin regulation.

SUBMITTER: Rui X 

PROVIDER: S-EPMC4132822 | biostudies-literature | 2014 Aug

REPOSITORIES: biostudies-literature