Plays a role in protein sorting and trafficking between the trans-Golgi network (TGN) and endosomes. Mediates the ARF- dependent recruitment of clathrin to the TGN and binds ubiquitinated proteins and membrane cargo molecules with a cytosolic acidic cluster-dileucine (AC-LL) motif. Monomer. Interacts with SORT1, SORL1, LRP3, GGA binding partner (GGABP) and P200. Interacts with GGA1 and GGA2. Binds to clathrin and activated ARFs. Binds RABEP1 and RABGEF1. Interacts with the membrane proteins M6PR/CD-MPR, IGF2R/CI-MPR and BACE1 and the accessory proteins SYNRG, EPN4, NECAP1, NECAP2 and AFTPH/aftiphilin. Interacts with TSG101 and UBC. Ubiquitously expressed. Belongs to the GGA protein family. 2 isoforms of the human protein are produced by alternative splicing. Note: This description may include information from UniProtKB.