Emerging Roles of Arf-Like GTP-Binding Proteins: from Membrane Trafficking to Cytoskeleton Dynamics and Beyond

Members of Rab and ADP-ribosylation factor (Arf) family of small GTP-binding (G) proteins regulate several aspects of intracellular transport and cytoskeleton organization. The phylogenetic analysis, combined with database mining approaches has led to the identification of Arf-like (Arl) G proteins as a sub-group of the Arf family with approximately 20 members in mammals. Arls are similar in structure to the Arfs, but exhibit immense diversity pertaining to their mechanisms of membrane recruitment, subcellular distribution and cellular functions. Only a few members of this sub-group are currently characterized, while information on the majority of Arl proteins remains scanty or is not known. In this review, we will cover our current understanding of the functions performed by Arl sub-family members, described under three broad categories: Arls involved in primary cilia formation and function, Arls engaged in secretory and endocytic transport, and Arls regulating microtubule and actin organization.