The phosphoinositide binding Phox Homology domain of uncharacterized SNX19-like plant proteins
The PX domain is a phosphoinositide (PI) binding module involved in targeting proteins to PI-enriched membranes. Members in this subfamily are uncharacterized plant proteins containing an N-terminal PXA domain, a central PX domain, and a C-terminal domain that is conserved in some sorting nexins (SNXs). This is the same domain architecture found in SNX19. SNX13 and SNX14 also contain these three domains but also contain a regulator of G protein signaling (RGS) domain in between the PXA and PX domains. 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. In addition to protein-lipid interaction, the PX domain may also be involved in protein-protein interaction.
Feature 1: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.