Characterization of BLOC-2, a complex containing the Hermansky-Pudlak syndrome proteins HPS3, HPS5 and HPS6

Traffic. 2004 Apr;5(4):276-83. doi: 10.1111/j.1600-0854.2004.0171.x.


Hermansky-Pudlak syndrome (HPS) defines a group of at least seven autosomal recessive disorders characterized by albinism and prolonged bleeding due to defects in the lysosome-related organelles, melanosomes and platelet-dense granules, respectively. Most HPS genes, including HPS3, HPS5 and HPS6, encode ubiquitously expressed novel proteins of unknown function. Here, we report the biochemical characterization of a stable protein complex named Biogenesis of Lysosome-related Organelles Complex-2 (BLOC-2), which contains the HPS3, HPS5 and HPS6 proteins as subunits. The endogenous HPS3, HPS5 and HPS6 proteins from human HeLa cells coimmunoprecipitated with each other from crude extracts as well as from fractions resulting from size-exclusion chromatography and density gradient centrifugation. The native molecular mass of BLOC-2 was estimated to be 340 +/- 64 kDa. As inferred from the biochemical properties of the HPS6 subunit, BLOC-2 exists in a soluble pool and associates to membranes as a peripheral membrane protein. Fibroblasts deficient in the BLOC-2 subunits HPS3 or HPS6 displayed normal basal secretion of the lysosomal enzyme beta-hexosaminidase. Our results suggest a common biological basis underlying the pathogenesis of HPS-3, -5 and -6 disease.

Publication types

  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Carrier Proteins / genetics*
  • Carrier Proteins / immunology
  • Carrier Proteins / metabolism
  • Chromatography, Gel
  • Hermanski-Pudlak Syndrome / genetics*
  • Hermanski-Pudlak Syndrome / immunology
  • Hermanski-Pudlak Syndrome / metabolism
  • Humans
  • Immunoblotting
  • Intracellular Signaling Peptides and Proteins
  • Multigene Family
  • Proteins


  • BLOC1S2 protein, human
  • Carrier Proteins
  • HPS3 protein, human
  • HPS5 protein, human
  • HPS6 protein, human
  • Intracellular Signaling Peptides and Proteins
  • Proteins