Structural Basis for the Phosphorylation-regulated Focal Adhesion Targeting of Type Iγ Phosphatidylinositol Phosphate Kinase (PIPKIγ) by Talin

Phosphatidylinositol-4,5-bisphosphate (PIP2) is a key lipid messenger that regulates myriad diverse cellular signaling pathways. To ensure specificity in disparate cellular events, PIP2 must be localized to specific sub-cellular sites. At PIP2-regulated focal adhesion (FA) sites, such localization is in part mediated via the recruitment and activation of PIP2-producing enzyme, type Iγ phosphatidylinositol phosphate kinase (PIPKIγ), by a phosphotyrosine binding (PTB) domain of talin. Transient phosphorylation of PIPKIγ at Y644 regulates the interaction and efficient FA targeting of PIPKIγ; however, the underlying structural basis remains elusive. We have determined the NMR structure of talin-1 PTB in complex with the Y644-phosphorylated PIPKIγ fragment (WVpYSPLH). As compared to canonical PTB domains that typically recognize the NPXpY turn motif from a variety of signaling proteins, our structure displays an unusual non-NPXpY-based recognition mode for talin-1 PTB where K357RW in β5 strand forms an antiparallel β-sheet with the VpYS of PIPKIγ. A specific electrostatic triad between K357/R358 of talin-1 PTB and the pY644 of PIPKIγ was observed, which is consistent with the mutagenesis and isothermal calorimetry data. Combined with previous in vivo data, our results provide a framework for understanding how phosphorylation of Y644 in PIPKIγ promotes its specific interaction with talin-1, leading to efficient local synthesis of PIP2 and dynamic regulation of integrin-mediated FA assembly.