α2E318A and α2GFFKRΔ integrin subunits rescue collagen binding when coupled to activation-deficient β1YA integrin subunits. (A) Lentiviral expression of wild-type and mutant α2 subunits in Itgβ1YA/YA embryonic stem cells in which both β1 intracellular tyrosines have been mutated to alanine. (B) The E318A and GFFKRΔ α2 mutants rescue soluble collagen binding of β1YA integrins. FITC-conjugated soluble collagen binding was measured using flow cytometry (above) and quantitated below. N = 3; mean and SD are shown. **P < .01 compared α2β1YA. (C) The activation state–specific monoclonal anti-β1 antibody 9EG7 binds wild-type β1 integrins (blue lines) but not β1YA integrins (gray shadow). Coupling of β1YA integrin subunits to α2E318A but not α2GFFKRΔ integrin subunits partially restores 9EG7 binding (red lines). Numbers indicate the percentage of 9EG7+ β1YA ES cells expressing wild-type or activated α2 integrins compared with untransfected β1YA ES cells.
