Specificity and Commonality of the Phosphoinositide-Binding Proteome Analyzed by Quantitative Mass Spectrometry

Phosphoinositides (PIPs) play key roles in signaling and disease. Using high-resolution quantitative mass spectrometry, we identified PIP-interacting proteins and profiled their binding specificities toward all seven PIP variants. This analysis revealed 405 PIP-binding proteins, which is greater than the total number of phospho- or ubiquitin-binding domains. Translocation and inhibitor assays of identified PIP-binding proteins confirmed that our methodology targets direct interactors. The PIP interactome encompasses proteins from diverse cellular compartments, prominently including the nucleus. Our data set revealed a consensus motif for PI(3,4,5)P3-interacting pleckstrin homology (PH) domains, which enabled in silico identification of phosphoinositide interactors. Members of the dedicator of cytokinesis family C exhibited specificity toward both PI(3,4,5)P3 and PI(4,5)P2. Structurally, this dual specificity is explained by a decreased number of positively charged residues in the L1 subdomain compared with DOCK1. The presented PIP-binding proteome and its specificity toward individual PIPs should be a valuable resource for the community.