The phosphoinositide binding Phox Homology domain of PX-RICS
The PX domain is a phosphoinositide (PI) binding module present in many proteins with diverse functions such as cell signaling, vesicular trafficking, protein sorting, and lipid modification, among others. RICS is a Rho GTPase-activating protein for cdc42 and Rac1. It is implicated in the regulation of postsynaptic signaling and neurite outgrowth. An N-terminal splicing variant of RICS containing additional PX and Src Homology 3 (SH3) domains, also called PX-RICS, is the main isoform expressed during neural development. PX-RICS is involved in neural functions including axon and dendrite extension, postnatal remodeling, and fine-tuning of neural circuits during early brain development. The PX domain is involved in targeting of proteins to PI-enriched membranes, and may also be involved in protein-protein interaction. The PX domain of PX-RICS specifically binds phosphatidylinositol 3-phosphate (PI3P), PI4P, and PI5P.
Feature 1:putative phosphoinositide binding site [chemical binding site]
Comment:A majority of PX domain containing proteins binds phosphatidylinositol-3-phosphate (PI3P) at this site. In some cases, other phosphoinositides, such as PI4P or PI(3,4)P2, are the preferred substrates.
Comment:based on the structures of phosphatidylinositol-3-phosphate bound to other members of this superfamily
Comment:Two basic residues are key in binding with phosphoinositides: one forms hydrogen bonds with the 3-phosphate of PI(3)P and another forms hydrogen bonds with the 4-and 5-hydroxyl groups of PI(3)P.