title: The α-subunit regulates stability of the metal ion at the ligand-associated metal ion-binding site in β3 integrins.
abstract: The aspartate in the prototypical integrin-binding motif Arg-Gly-Asp binds the integrin βA domain of the β-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 α-subunits of the two β3 integrins αIIbβ3 and αVβ3, but a potential role of this interaction on stability of the metal ion at LIMBS in β3 integrins has not been explored. Equilibrium molecular dynamics simulations of fully hydrated β3 integrin ectodomains revealed strikingly different conformations of LIMBS in unliganded αIIbβ3 versus αVβ3, the result of stronger interactions of LIMBS with αV, which reduce stability of the LIMBS metal ion in αVβ3. Replacing the αIIb-LIMBS interface residue Phe(191) in αIIb (equivalent to Trp(179) in αV) with Trp strengthened this interface and destabilized the metal ion at LIMBS in αIIbβ3; a Trp(179) to Phe mutation in αV produced the opposite but weaker effect. Consistently, an F191/W substitution in cellular αIIbβ3 and a W179/F substitution in αVβ3 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 αVβ3 structures in the absence of ligand and provide new insights into the mechanisms of integrin regulation.
authors: Leukocyte Biology and Inflammation Program and Massachusetts General Hospital and Harvard Medical School, Charlestown, Massachusetts 02129.
authors: Xianliang
authors: X
authors: Rui
authors: Departments of Bioengineering and Mechanical Engineering, University of California, Berkeley, California 94720.
authors: Mehrdad
authors: M
authors: Mehrbod
authors: Structural Biology Program, Department of Medicine, Massachusetts General Hospital and Harvard Medical School, Charlestown, Massachusetts 02129 and.
authors: Johannes F
authors: JF
authors: Van Agthoven
authors: Leukocyte Biology and Inflammation Program and Massachusetts General Hospital and Harvard Medical School, Charlestown, Massachusetts 02129.
authors: Saurabh
authors: S
authors: Anand
authors: Structural Biology Program, Department of Medicine, Massachusetts General Hospital and Harvard Medical School, Charlestown, Massachusetts 02129 and.
authors: Jian-Ping
authors: JP
authors: Xiong
authors: Departments of Bioengineering and Mechanical Engineering, University of California, Berkeley, California 94720. Electronic address: mofrad@berkeley.edu.
authors: Mohammad R K
authors: MRK
authors: Mofrad
authors: Leukocyte Biology and Inflammation Program and Massachusetts General Hospital and Harvard Medical School, Charlestown, Massachusetts 02129; Structural Biology Program, Department of Medicine, Massachusetts General Hospital and Harvard Medical School, Charlestown, Massachusetts 02129 and. Electronic address: aarnaout1@mgh.harvard.edu.
authors: M Amin
authors: MA
authors: Arnaout
mesh_terms: D020816:Amino Acid Motifs; D001665:Binding Sites; D002413:Cations, Divalent / Q000737:chemistry; D006801:Humans; D039302:Integrin alphaVbeta3 / Q000737:chemistry* / Q000235:genetics; D039661:Integrin beta3 / Q000737:chemistry* / Q000235:genetics; D008345:Manganese / Q000737:chemistry*; D019039:Platelet Glycoprotein GPIIb-IIIa Complex / Q000737:chemistry* / Q000235:genetics
chemical_list: D002413:Cations, Divalent; C061248:ITGB3 protein, human; D039302:Integrin alphaVbeta3; D039661:Integrin beta3; D019039:Platelet Glycoprotein GPIIb-IIIa Complex; D008345:Manganese
keywords: Cell Adhesion; Cell Biology; Integrin; Molecular Dynamics; Signal Transduction