The dynamic Rab11-FIPs

The Rab11-FIPs (Rab11-family interacting proteins; also known as FIPs) constitute an evolutionarily conserved protein family that act as effector molecules for multiple Rab and Arf (ADP-ribosylation factor) GTPases. They were initially characterized by their ability to bind Rab11 subfamily members via a highly-conserved C-terminal RBD (Rab11-binding domain). Resolution of the crystal structure of Rab11 in complex with FIPs revealed that the RBD mediates homodimerization of the FIP molecules, creating two symmetrical interfaces for Rab11 binding and leading to the formation of a heterotetrameric complex between two FIP and two Rab11 molecules. The FIP proteins are encoded by five genes and alternative splicing has been reported. Based on primary structure, the FIPs were subcategorized into two classes: class I [Rip11, FIP2 and RCP (Rab-coupling protein)] and class II (FIP3 and FIP4). Recent studies have identified the FIPs as key players in the regulation of multiple distinct membrane trafficking events. In this mini-review, we summarize the Rab11-FIP field and discuss, at molecular and cellular levels, the recent findings on FIP function.