Coat protein that is involved in the localization of trans-Golgi network (TGN) membrane proteins that contain acidic cluster sorting motifs. Controls the endosome-to-Golgi trafficking of furin and mannose-6-phosphate receptor by connecting the acidic-cluster-containing cytoplasmic domain of these molecules with the adapter-protein complex-1 (AP-1) of endosomal clathrin-coated membrane pits (By similarity). Associates with AP-1 and AP-3 but not with AP-2 complexes (By similarity). Interacts with FURIN (PubMed:9695949). Forms a ternary complex with FURIN and AP-1 (By similarity). Interacts with PKD2 (via acidic region) (PubMed:15692563). Interacts with SORL1 (By similarity). Localizes in the perinuclear region, probably the TGN. Belongs to the PACS family.