Role of the beta-subunit arginine/lysine finger in integrin heterodimer formation and function

• Published in: The Journal of immunology (1950) 2008-02, Vol.180 (3), p.1713-1718
• Main Authors: Gupta, Vineet, Alonso, José Luis, Sugimori, Takashi, Essafi, Makram, Issafi, Makram, Xiong, Jiang-Ping, Arnaout, M Amin
• Format: Article
• Language: English
• Subjects: Amino Acid Sequence; Amino Acid Substitution; Arginine - chemistry; Arginine - genetics; CD11a Antigen - chemistry; CD11a Antigen - physiology; CD18 Antigens - chemistry; CD18 Antigens - genetics; CD18 Antigens - physiology; Cell Line; Cell Membrane - chemistry; Dimerization; Humans; Integrin beta3 - chemistry; Integrin beta3 - genetics; Integrin beta3 - physiology; Lysine - chemistry; Lysine - genetics; Molecular Sequence Data; Mutation; Protein Conformation; Protein Subunits - chemistry; Protein Subunits - genetics; Protein Subunits - physiology
• ISSN: 0022-1767; 1550-6606
• DOI: 10.4049/jimmunol.180.3.1713

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.