title: BLOC-3, a protein complex containing the Hermansky-Pudlak syndrome gene products HPS1 and HPS4.
abstract: The Hermansky-Pudlak syndrome (HPS) is a genetic disorder characterized by defective lysosome-related organelles. HPS results from mutations in either one of six human genes named HPS1 to HPS6, most of which encode proteins of unknown function. Here we report that the human HPS1 and HPS4 proteins are part of a complex named BLOC-3 (for biogenesis of lysosome-related organelles complex 3). Co-immunoprecipitation experiments demonstrated that epitope-tagged and endogenous HPS1 and HPS4 proteins assemble with each other in vivo. The HPS1.HPS4 complex is predominantly cytosolic, with a small amount being peripherally associated with membranes. Size exclusion chromatography and sedimentation velocity analyses of the cytosolic fraction indicate that HPS1 and HPS4 form a moderately asymmetric protein complex with a molecular mass of approximately 175 kDa. HPS4-deficient fibroblasts from light ear mice display normal distribution and trafficking of the lysosomal membrane protein, Lamp-2, in contrast to fibroblasts from AP-3-deficient pearl mice (HPS2), which exhibit increased trafficking of this lysosomal protein via the plasma membrane. Similarly, light ear fibroblasts display an apparently normal accumulation of Zn2+ in intracellular vesicles, unlike pearl fibroblasts, which exhibit a decreased intracellular Zn2+ storage. Taken together, these observations demonstrate that the HPS1 and HPS4 proteins are components of a cytosolic complex that is involved in the biogenesis of lysosomal-related organelles by a mechanism distinct from that operated by AP-3 complex.
authors.affiliation: Cell Biology and Metabolism Branch, NICHD, National Institutes of Health, Bethesda, Maryland 20892, USA.
authors.forename: José A
authors.initials: JA
authors.lastname: Martina
authors.forename: Kengo
authors.initials: K
authors.lastname: Moriyama
authors.forename: Juan S
authors.initials: JS
authors.lastname: Bonifacino
mesh_terms: D033963:Adaptor Protein Complex 3; D000818:Animals; D015703:Antigens, CD / Q000378:metabolism; D002460:Cell Line; D055598:Chemical Phenomena; D002627:Chemistry, Physical; D002850:Chromatography, Gel; D003600:Cytosol / Q000737:chemistry; D004591:Electrophoresis, Polyacrylamide Gel; D005347:Fibroblasts / Q000378:metabolism; D020662:Guanine Nucleotide Exchange Factors; D022861:Hermanski-Pudlak Syndrome / Q000235:genetics; D006801:Humans; D015151:Immunoblotting; D007163:Immunosorbent Techniques; D051907:Lysosomal Membrane Proteins; D008247:Lysosomes / Q000378:metabolism; D008565:Membrane Proteins / Q000737:chemistry* / Q000235:genetics; D051379:Mice; D008856:Microscopy, Fluorescence; D008970:Molecular Weight; D011506:Proteins / Q000737:chemistry* / Q000235:genetics; D012441:Saccharomyces cerevisiae / Q000235:genetics; D014162:Transfection; D020798:Two-Hybrid System Techniques; D015032:Zinc / Q000378:metabolism
chemical_list: D033963:Adaptor Protein Complex 3; D015703:Antigens, CD; D020662:Guanine Nucleotide Exchange Factors; C102160:HPS1 protein, human; C451752:HPS4 protein, human; C491131:Hps1 protein, mouse; D051907:Lysosomal Membrane Proteins; D008565:Membrane Proteins; D011506:Proteins; D015032:Zinc