An unbiased genetic approach was used to identify a specific amino acid residue in the α(IIb) subunit important for the ligand binding function of the integrin α(IIb)β. Chemically mutagenized cells were selected flow cytometry based on their inability to bind the ligand mimetic antibody PAC1 and a cell line containing a single amino acid substitution in α(IIb) at position 224 (D→V) was identified. Although well expressed on the surface of transfected cells, α(IIb)D224Vβ3 as well as α(IIb)D224β3 did not bind α(IIb)β3-specific ligands or a RGD peptide, a ligand shared in common with α(v)β3. Insertion of exon 5 of α(IIb), residues G193-W235, into the backbone of the α(v) subunit did not enable the chimeric receptor to bind α(IIb)β3-specific ligands. However, the chimeric receptor was still capable of binding to a RGB affinity matrix, α(IIb)D224 is not well conserved among other integrin α 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 α 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 α(IIb)β3 receptor.
ASJC Scopus subject areas
- Cell Biology