The ADP ribosylation factor (Arf) family small GTPases, consisting of Arf, Arf-like (Arl), and Sar proteins, can recruit a specific set of effectors to the membrane, such as coat complexes and membrane tethers, to modulate vesicular and lipid trafficking (Donaldson and Jackson, 2011). Arf proteins are activated by guanine nucleotide exchange factors (GEFs) that catalyze the switch from the GDP-bound inactive form to the GTP-bound active form. Human GBF/Gea and BIG/Sec7 proteins, including BIG1, BIG2, and GBF1, are a family of Sec7 domain-containing Arf GEFs, which all consist of six conserved domains: an N-terminal dimerization and cyclophilin binding (DCB) domain, a homology upstream of Sec7 (HUS) domain
