Genome-Wide Identification and Functional Annotation of Dual Specificity Protein- and Lipid-Binding Modules That Modulate Protein Interactions at the Membrane

Emerging evidence indicates that membrane lipids regulate protein networking by directly interacting with protein-interaction domains (PIDs). As a pilot study to identify and functionally annodate lipid-binding PIDs on a genomic scale, we performed experimental and computational studies of PDZ domains. Characterization of 70 PDZ domains showed that 40% had submicromolar membrane affinity. Using a computational model built from these data, we predicted the membrane binding properties of 2000 PDZ domains from 20 species. The accuracy of the prediction was experimentally validated for 26 PDZ domains. We also subdivided lipid-binding PDZ domains into three classes based on the interplay between membrane and protein binding sites. For different classes of PDZ domains, lipid binding regulates their protein interactions by different mechanisms. Functional studies of a PDZ domain protein, rhophilin2 suggest that all classes of lipid binding PDZ domains serve as genuine dual-specificity modules regulating protein interactions at the membrane under physiological conditions.