Structural Basis for Paxillin Binding and Focal Adhesion Targeting of β-Parvin

beta-Parvin is a cytoplasmic adaptor protein that localizes to focal adhesions where it interacts with integrin-linked kinase and is involved in linking integrin receptors to the cytoskeleton. It has been reported that despite high sequence similarity to beta-parvin, beta-parvin does not bind paxillin, suggesting distinct interactions and cellular functions for these two closely related parvins. Here, we reveal that beta-parvin binds directly and specifically to leucine-aspartic acid repeat (LD) motifs in paxillin via its C-terminal calponin homology (CH2) domain. We present the co-crystal structure of beta-parvin CH2 domain in complex with paxillin LD1 motif to 2.9 angstrom resolution and find that the interaction is similar to that previously observed between beta-parvin and paxillin LD1. We also present crystal structures of unbound beta-parvin CH2 domain at 2.1 angstrom and 2.0 angstrom resolution that show significant conformational flexibility in the N-terminal alpha-helix, suggesting an induced fit upon paxillin binding. We find that beta-parvin has specificity for the LD1, LD2, and LD4 motifs of paxillin, with K-D values determined to 27, 42, and 73 mu M, respectively, by surface plasmon resonance. Furthermore, we show that proper localization of beta-parvin to focal adhesions requires both the paxillin and integrin-linked kinase binding sites and that paxillin is important for early targeting of beta-parvin. These studies provide the first molecular details of beta-parvin binding to paxillin and help define the requirements for beta-parvin localization to focal adhesions.