Structural basis for Rab11-dependent membrane recruitment of a family of Rab11-interacting protein 3 (FIP3)/Arfophilin-1

Family of Rabl1-interacting protein (FIP)3/Arfophlin-1 and FIP4/ Arfophilin-2 are dual effectors for Rabll and ADP ribosylation factor (ARF)5/ARF6, which are involved in membrane delivery from recycling enclosomes to the plasma membrane during cytokinesis. Here, we define the distinct C-terminal binding regions of FIP3 and FIP4 for Rabll and ARF5/ARF6. Furthermore, we determined the crystal structure of Rab11 in complex with the Rabll-binding domain (REID) of FIP3. The long amphiphilic alpha-helix of FIP3-RBD forms a parallel coiled-coil homodimer, with two symmetric interfaces with two Rabl 1 molecules. The hydrophobic side of the RBD helix is involved in homodimerization and mediates the interaction with the Rabll 1 switch 1 region, whereas the opposite hydrophilic side interacts with the Rabll switch 2 and is the major factor contributing to the binding specificity. The bivalent interaction of FlP3 with Rabll at the C terminus allows FlP3 to coordinately function with other binding partners, including ARFs.