A single amino acid substitution in β3 (Asp119 → Tyr) abrogates the ligand binding function of β3 integrins and alters the divalent cation conformation of the platelet integrin α(IIb)β3 (GPIIb-IIIa). This aspartic acid residue resides within a conserved cluster of oxygenated residues that may provide ligands for the coordination of divalent cations. To assign function to the other oxygenated residues in this group (Ser121, Ser123, Asp126, Asp127, and Ser130), each of these amino acids in β3 was individually substituted by alanine. None of these amino acid substitutions altered heterodimer formation or surface expression. However, the substitutions had differential effects on receptor function. Substitution at positions Asp119 or Ser121 produced a complete loss of receptor function. Cells expressing these mutants failed to adhere to fibrinogen, failed to bind activation-independent ligand-mimetic peptides, and did not bind the ligand-mimetic mAb PAC1 following activation of the receptor. Similarly, cells expressing β3 with a substitution at Ser123 also failed to adhere to fibrinogen and did not bind RGD peptide or mAb PAC1. These cells did retain the capacity to bind an α(IIb)β3-specific, high affinity peptidomimetic, but occupancy did not induce the conformational change from resting to activated state observed following occupancy of the wild type receptor. Substitution at positions Asp126, Asp127, or Ser130 had no effect on ligand binding function. These data indicate that Asp110, along with Ser121 and Ser123, plays an integral role in the ligand binding function of α(IIb)β3.
|Original language||English (US)|
|Number of pages||7|
|Journal||Journal of Biological Chemistry|
|State||Published - 1994|
ASJC Scopus subject areas
- Molecular Biology
- Cell Biology