title: Role of the beta-subunit arginine/lysine finger in integrin heterodimer formation and function.
abstract: Formation of the integrin alphabeta heterodimer is essential for cell surface expression and function. At the core of the alphabeta interface is a conserved Arg/Lys "finger" from the beta-subunit that inserts into a cup-like "cage" formed of two layers of aromatic residues in the alpha-subunit. We evaluated the role of this residue in heterodimer formation in an alphaA-lacking and an alphaA-containing integrin alphaVbeta3 and alphaMbeta2 (CD11b/CD18), respectively. Arg261 of beta3 was mutated to Ala or Glu; the corresponding Lys252 of beta2 was mutated to Ala, Arg, Glu, Asp, or Phe; and the effects on heterodimer formation in each integrin examined by ELISA and immunoprecipitation in HEK 293 cells cotransfected with plasmids encoding the alpha- and beta-subunits. The Arg261Glu (but not Arg261Ala) substitution significantly impaired cell surface expression and heterodimer formation of alphaVbeta3. Although Lys252Arg, and to a lesser extent Lys252Ala, were well tolerated, each of the remaining substitutions markedly reduced cell surface expression and heterodimer formation of CD11b/CD18. Lys252Arg and Lys252Ala integrin heterodimers displayed a significant increase in binding to the physiologic ligand iC3b. These data demonstrate an important role of the Arg/Lys finger in formation of a stable integrin heterodimer, and suggest that subtle changes at this residue affect the activation state of the integrin.
authors.affiliation: Division of Nephrology, Leukocyte Biology and Inflammation Program, Structural Biology Program, Massachusetts General Hospital and Harvard Medical School, 149 13th Street, Charlestown, MA 02129, USA
authors.forename: Vineet
authors.initials: V
authors.lastname: Gupta
authors.forename: José Luis
authors.initials: JL
authors.lastname: Alonso
authors.forename: Takashi
authors.initials: T
authors.lastname: Sugimori
authors.forename: Makram
authors.initials: M
authors.lastname: Essafi
authors.forename: Makram
authors.initials: M
authors.lastname: Issafi
authors.forename: Jiang-Ping
authors.initials: JP
authors.lastname: Xiong
authors.forename: M Amin
authors.initials: MA
authors.lastname: Arnaout
mesh_terms: D000595:Amino Acid Sequence; D019943:Amino Acid Substitution; D001120:Arginine / Q000737:chemistry / Q000235:genetics; D040881:CD11a Antigen / Q000737:chemistry* / Q000502:physiology*; D018821:CD18 Antigens / Q000737:chemistry* / Q000235:genetics / Q000502:physiology*; D002460:Cell Line; D002462:Cell Membrane / Q000737:chemistry; D019281:Dimerization; D006801:Humans; D039661:Integrin beta3 / Q000737:chemistry* / Q000235:genetics / Q000502:physiology*; D008239:Lysine / Q000737:chemistry / Q000235:genetics; D008969:Molecular Sequence Data; D009154:Mutation; D011487:Protein Conformation; D021122:Protein Subunits / Q000737:chemistry / Q000235:genetics / Q000502:physiology
chemical_list: D040881:CD11a Antigen; D018821:CD18 Antigens; D039661:Integrin beta3; D021122:Protein Subunits; D001120:Arginine; D008239:Lysine