Role of the beta-subunit arginine/lysine finger in integrin heterodimer formation and function.
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.
Gupta
Vineet
V
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
Alonso
José Luis
JL
Sugimori
Takashi
T
Essafi
Makram
M
Issafi
Makram
M
Xiong
Jiang-Ping
JP
Arnaout
M Amin
MA
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
D040881:CD11a Antigen; D018821:CD18 Antigens; D039661:Integrin beta3; D021122:Protein Subunits; D001120:Arginine; D008239:Lysine