Clustering in integrin binding

The adhesiveness of integrin binding is determined by both the affinity of individual heterodimers for their ligand and the clustering of multiple heterodimers. Kim et al. show, on page 1241, that clustering does not precede binding but rather functions in adhesion strengthening following binding to multivalent ligands.To probe the question of whether clustering or affinity are primary factors in leukocyte integrin binding, Kim et al. devised a FRET system in which either the α or β subunits of the integrin LFA-1 (α_Lβ₂) were labeled with nondimerizing forms of YFP and CFP. Under basal conditions, no micro-clustering was evident, as cells expressing α_L-mCFP, α_L-mYFP, and wild-type β₂ showed little FRET. Nor did the researchers observe FRET when cells were stimulated to activate LFA-1 adhesiveness. Furthermore, activation of LFA-1 with cytoskeletal-disrupting...