FIGURE 7.

The SNX-PXB proteins possess overlapping binding sites for PtdIns3P and PtdIns(4,5)P₂in vitro. A, membrane binding of SNX20 and SNX21Δ93 to liposomes containing different PI combinations was assessed by incubation following ultracentrifugation and subsequent protein content analysis of supernatant (S) and pellet (P) fractions. B, mutation of SNX20 and SNX21Δ93 at the key PtdIns3P-binding arginine side chain prevents binding to PtdIns3P but still allows interaction with negatively charged Folch membranes, and liposomes containing PtdIns(4,5)P₂. C, SNX20 and SNX21 PX domain models reveal three distinct conserved basic clusters based on homology modeling. D, arginine and lysine residues forming these three clusters were mutated to glutamine to test for PI binding disruption.