A Mutation in the  Subunit of the Platelet Integrin IIbβ3 Identifies a Novel Region Important for Ligand Binding

Open Access
Publisher Website
Google Scholar
Abstract
An unbiased genetic approach was used to identify a specific amino acid residue in the IIb subunit important for the ligand binding function of the integrin IIbβ. Chemically mutagenized cells were selected by flow cytometry based on their inability to bind the ligand mimetic antibody PAC1 and a cell line containing a single amino acid substitution in IIb at position 224 (D→V) was identified. Although well expressed on the surface of transfected cells, IIbD224Vβ3 as well as IIbD224Aβ3 did not bind IIbβ3-specific ligands or a RGD peptide, a ligand shared in common with vβ3. Insertion of exon 5 of IIb, residues G193-W235, into the backbone of the v subunit did not enable the chimeric receptor to bind IIbβ3-specific ligands. However, the chimeric receptor was still capable of binding to a RGD affinity matrix. IIbD224 is not well conserved among other integrin  subunits and is located in a region of significant variability. In addition, amino acid D224 lies within a predicted loop of the recently proposed β-propeller model for integrin  subunits and is adjacent to a loop containing amino acid residues previously implicated in receptor function. These data support a role for this region in ligand binding function of the IIbβ3 receptor.