Molecular Basis of Phosphatidylinositol 4-Phosphate and ARF1 GTPase Recognition by the FAPP1 Pleckstrin Homology (PH) Domain

• DOI: 10.1074/jbc.m111.233015
• Publication Date: 2011-03-23T03:54:15Z
• Authors: Ju He; Jordan L. Scott; Annie Heroux; Siddhartha Roy; Marc Lenoir; Michael Overduin; Robert V. Stahelin; Tatiana G. Kutate...
• Keywords: Protein Folding; 0303 health sciences; Biological Transport; Intracellular Membranes; Crystallography, X-Ray; Protein Structure, Tertiary; Structure-Activity Relationship; 03 medical and health sciences; Phosphatidylinositol Phosphates; Mutagenesis; Humans; ADP-Ribosylation Factor 1; Nuclear Magnetic Resonance, Biomolecular; Adaptor Proteins, Signal Transducing; Protein Binding; trans-Golgi Network

Four-phosphate-adaptor protein 1 (FAPP1) regulates secretory transport from the trans-Golgi network (TGN) to the plasma membrane. FAPP1 is recruited to the Golgi through binding of its pleckstrin homology (PH) domain to phosphatidylinositol 4-phosphate (PtdIns(4)P) and a small GTPase ADP-ribosylation factor 1 (ARF1). Despite the critical role of FAPP1 in membrane trafficking, the molecular basis of its dual function remains unclear. Here, we report a 1.9 Å resolution crystal structure of the FAPP1 PH domain and detail the molecular mechanisms of the PtdIns(4)P and ARF1 recognition. The FAPP1 PH domain folds into a seven-stranded β-barrel capped by an α-helix at one edge, whereas the opposite edge is flanked by three loops and the β4 and β7 strands that form a lipid-binding pocket within the β-barrel. The ARF1-binding site is located on the outer side of the β-barrel as determined by NMR resonance perturbation analysis, mutagenesis, and measurements of binding affinities. The two binding sites have little overlap, allowing FAPP1 PH to associate with both ligands simultaneously and independently. Binding to PtdIns(4)P is enhanced in an acidic environment and is required for membrane penetration and tubulation activity of FAPP1, whereas the GTP-bound conformation of the GTPase is necessary for the interaction with ARF1. Together, these findings provide structural and biochemical insight into the multivalent membrane anchoring by the PH domain that may augment affinity and selectivity of FAPP1 toward the TGN membranes enriched in both PtdIns(4)P and GTP-bound ARF1.