Research article

Association of the Hermansky-Pudlak syndrome type-3 protein with clathrin

Amanda Helip-Wooley¹ , Wendy Westbroek¹ , Heidi Dorward¹ , Mieke Mommaas² , Raymond E Boissy³ , William A Gahl¹ and Marjan Huizing¹

¹  Section on Human Biochemical Genetics, Medical Genetics Branch, National Human Genome Research Institute, NIH, Bethesda MD, USA

²  Department of Molecular Cell Biology, Leiden University Medical Center, Leiden, Netherlands

³  Department of Dermatology, University of Cincinnati College of Medicine, OH, USA

author email corresponding author email

BMC Cell Biology 2005, 6:33doi:10.1186/1471-2121-6-33

Published:	13 September 2005

Abstract

Background

Hermansky-Pudlak syndrome (HPS) is a disorder of lysosome-related organelle biogenesis characterized by oculocutaneous albinism and prolonged bleeding. These clinical findings reflect defects in the formation of melanosomes in melanocytes and dense bodies in platelets. HPS type-3 (HPS-3) results from mutations in the HPS3 gene, which encodes a 1004 amino acid protein of unknown function that contains a predicted clathrin-binding motif (LLDFE) at residues 172–176.

Results

Clathrin was co-immunoprecipitated by HPS3 antibodies from normal but not HPS3 null melanocytes. Normal melanocytes expressing a GFP-HPS3 fusion protein demonstrated partial co-localization of GFP-HPS3 with clathrin following a 20°C temperature block. GFP-HPS3 in which the predicted clathrin-binding domain of HPS3 was mutated (GFP-HPS3-delCBD) did not co-localize with clathrin under the same conditions. Immunoelectron microscopy of normal melanocytes expressing GFP-HPS3 showed co-localization of GFP-HPS3 with clathrin, predominantly on small vesicles in the perinuclear region. In contrast, GFP-HPS3-delCBD did not co-localize with clathrin and exhibited a largely cytoplasmic distribution.

Conclusion

HPS3 associates with clathrin, predominantly on small clathrin-containing vesicles in the perinuclear region. This association most likely occurs directly via a functional clathrin-binding domain in HPS3. These results suggest a role for HPS3 and its protein complex, BLOC-2, in vesicle formation and trafficking.