This family would appear to be the second of the two larger subunits of the fifth Adaptor-Protein complex, AP-5. Adaptor protein (AP) complexes facilitate the trafficking of cargo from one membrane compartment of the cell to another by recruiting other proteins to particular types of vesicles. AP-5 is involved in trafficking proteins from endosomes towards other membranous compartments [2]. There are genetic links between AP-5 and hereditary spastic paraplegia, a group of human genetic disorders characterised by progressive spasticity in the lower limbs [1].

1: A genome-scale DNA repair RNAi screen identifies SPG48 as a novel gene associated with hereditary spastic paraplegia. Slabicki M, Theis M, Krastev DB, Samsonov S, Mundwiller E, Junqueira M, Paszkowski-Rogacz M, Teyra J, Heninger AK, Poser I, Prieur F, Truchetto J, Confavreux C, Marelli C, Durr A, Camdessanche JP, Brice A, Shevchenko A, Pisabarro MT, Stevanin G, Buchholz F; PLoS Biol. 2010;8:e1000408. PMID:20613862

2: The fifth adaptor protein complex. Hirst J, Barlow LD, Francisco GC, Sahlender DA, Seaman MN, Dacks JB, Robinson MS; PLoS Biol. 2011;9:e1001170. PMID:22022230

3: And now there are five: a new player in intracellular trafficking pathways. Huang S; PLoS Biol. 2011;9:e1001173. PMID:22022232