Human GGA protein family members.

<p>The GGA proteins were discovered almost simultaneously by five laboratories studying different aspects of membrane trafficking [<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0129047#pone.0129047.ref014" target="_blank">14</a>, <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0129047#pone.0129047.ref049" target="_blank">49</a>–<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0129047#pone.0129047.ref052" target="_blank">52</a>]. The protein family consists of three members: GGA1, GGA2, and GGA3. GGAs are recruited from the cytosol onto the Golgi where they mediate the transport of cargo to endosomes/lysosomes. GGAs consist of four domains: the N-terminal VHS domain (Vps27, Hrs, and STAM); the GAT domain (GGA and Tom1), which contains two predicted coiled-coil domains; the hinge region, which contains one or more clathrin-binding sites; and the GAE domain (gamma-adaptin ear homology). The VHS domain is responsible for cargo recognition and binding via the AC-LL motifs in the cargo [<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0129047#pone.0129047.ref006" target="_blank">6</a>, <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0129047#pone.0129047.ref033" target="_blank">33</a>, <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0129047#pone.0129047.ref053" target="_blank">53</a>]. Membrane recruitment is provided by the GAT domain through ARF-GTP binding. Recently, the GAT C-terminal domains of GGA1 and GGA3 (but not GGA2) have also been shown to bind ubiquitin [<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0129047#pone.0129047.ref054" target="_blank">54</a>]. A distinct set of accessory proteins can bind to the GAE domain of GGAs, including rabaptin-5 [<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0129047#pone.0129047.ref055" target="_blank">55</a>], epsin R (Enthoprotin or Clint) [<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0129047#pone.0129047.ref056" target="_blank">56</a>–<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0129047#pone.0129047.ref059" target="_blank">59</a>], γ-synergin [<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0129047#pone.0129047.ref014" target="_blank">14</a>, <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0129047#pone.0129047.ref060" target="_blank">60</a>], p56, and p200 [<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0129047#pone.0129047.ref060" target="_blank">60</a>]. Shown are the GGA deletion mutants used in this study (lower left panel). The antibodies used, directed against GGA1 (H215/Santa Cruz), GGA2 (BD), and GGA3 (BD), bind to the hinge regions of GGAs as indicated (upper left panel).