The Novel S527F Mutation in the Integrin {beta}3 Chain Induces a High Affinity {alpha}IIb{beta}3 Receptor by Hindering Adoption of the Bent Conformation

• Published in: The Journal of biological chemistry Vol. 284; no. 22; pp. 14914 - 14920
• Main Authors: Vanhoorelbeke, Karen, De Meyer, Simon F, Pareyn, Inge, Melchior, Chantal, Plancon, Sebastien, Margue, Christiane, Pradier, Olivier, Fondu, Pierre, Kieffer, Nelly, Springer, Timothy A, Deckmyn, Hans
• Format: Journal Article
• Language: English
• Published: 29.05.2009
• ISSN: 0021-9258; 1083-351X
• DOI: 10.1074/jbc.M809167200

Three heterozygous mutations were identified in the genes encoding platelet integrin receptor {alpha}IIbb3 in a patient with an ill defined platelet disorder: one in the b3 gene (S527F) and two in the {alpha}IIb gene (R512W and L841M). Five stable Chinese hamster ovary cell lines were constructed expressing recombinant {alpha}IIbb3 receptors bearing the individual R512W, L841M, or S527F mutation; both the R512W and L841M mutations; or all three mutations. All receptors were expressed on the cell surface, and mutations R512W and L841M had no effect on integrin function. Interestingly, the b3 S527F mutation produced a constitutively active receptor. Indeed, both fibrinogen and the ligand-mimetic antibody PAC-1 bound to non- activated {alpha}IIbb3 receptors carrying the S527F mutation, indicating that the conformation of this receptor was altered and corresponded to the high affinity ligand binding state. In addition, the conformational change induced by S527F was evident from basal anti-ligand-induced binding site antibody binding to the receptor. A molecular model bearing this mutation was constructed based on the crystal structure of {alpha}IIbb3 and revealed that the S527F mutation, situated in the third integrin epidermal growth factor-like (I-EGF3) domain, hindered the {alpha}IIbb3 receptor from adopting a wild type-like bent conformation. Movement of I-EGF3 into a cleft in the bent conformation may be hampered both by steric hindrance between Phe super(527) in b3 and the calf-1 domain in {alpha}IIb and by decreased flexibility between I-EGF2 and I-EGF3.