The structures and function of GGAs, the traffic controllers at the TGN sorting crossroads

GGAs (Golgi-localizing, gamma-adaptin ear homology domain, ARF-binding proteins) are a family of monomeric clathrin adaptor proteins that are conserved from yeasts to humans. Data published during the past four years have provided detailed pictures of the localization, domain organization and structure-function relationships of GGAs. GGAs possess four conserved functional domains, each of which interacts with cargo proteins including mannose 6-phosphate receptors, the small GTPase ARIF, clathrin, or accessory proteins including Rabaptin-5 and gamma-synergin. Together with or independent of the adaptor protein complex AP-1, GGAs regulate selective transport of cargo proteins, such as mannose 6-phosphate receptors, from the trans-Golgi network to endosomes mediated by clathrin-coated vesicles.