The phosphoinositide binding Phox Homology domain of Sorting Nexins 5 and 6
The PX domain is a phosphoinositide (PI) binding module present in many proteins with diverse functions. Sorting nexins (SNXs) make up the largest group among PX domain containing proteins. They are involved in regulating membrane traffic and protein sorting in the endosomal system. The PX domain of SNXs binds PIs and targets the protein to PI-enriched membranes. SNXs differ from each other in PI-binding specificity and affinity, and the presence of other protein-protein interaction domains, which help determine subcellular localization and specific function in the endocytic pathway. Members of this subfamily include SNX5, SNX6, and similar proteins. They contain a Bin/Amphiphysin/Rvs (BAR) domain, which detects membrane curvature, C-terminal to the PX domain, similar to other sorting nexins including SNX1-2. The PX-BAR structural unit helps determine the specific membrane-targeting of some SNXs. SNX5 and SNX6 may be components of the retromer complex, a membrane coat multimeric complex required for endosomal retrieval of lysosomal hydrolase receptors to the Golgi, acting as a mammalian equivalent of yeast Vsp17p.
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.