canonical GAT domain found in fungal ADP-ribosylation factor (Arf)-binding proteins (GGAs)
GGAs, also called Golgi-localized gamma-ear-containing Arf-binding proteins, belong to a family of ubiquitously expressed, monomeric, motif-binding cargo/clathrin adaptor proteins that regulate clathrin-mediated trafficking of cargo proteins from the trans-Golgi network (TGN) to endosomes. Two GGAs (Gga1p and Gga2p) have been identified in the budding yeast Saccharomyces cerevisiae. Yeast GGAs play important roles in the carboxypeptidase Y (CPY) pathway, vacuole biogenesis, alpha-factor maturation, and interactions with clathrin. They have a multidomain structure consisting of VHS (Vps27/Hrs/ STAM), GAT (GGA and TOM), hinge, and GAE (gamma-adaptin ear) domains. Both Gga1p and Gga2p function as effectors of Arf in yeast. They interact with Arf1p and Arf2p in a GTP-dependent manner. Moreover, Gga2p mediates sequential ubiquitin-independent and ubiquitin-dependent steps in the trafficking of ARN1, a ferrichrome transporter in S. cerevisiae, from the TGN to the vacuole. It also acts as a phosphatidylinositol 4-phosphate effector at the Golgi exit, which binds directly to the TGN PtdIns(4)-kinase Pik1p and contributes to Pik1p recruitment. In addition, Gga2p is required for sorting of the yeast siderophore iron transporter1 (Sit1) to the vacuolar pathway. The GAT domain of GGAs interacts with class I GTP-bound form of Arf proteins, Rabaptin-5, ubiquitin, and/or the tumor susceptibility gene 101 product (TSG101).