A divalent interaction between HPS1 and HPS4 is required for the formation of the biogenesis of lysosome-related organelle complex-3 (BLOC-3)

• Published in: Biochimica et biophysica acta Vol. 1833; no. 3; pp. 468 - 478
• Main Authors: Carmona-Rivera, Carmelo, Simeonov, Dimitre R., Cardillo, Nicholas D., Gahl, William A., Cadilla, Carmen L.
• Format: Journal Article
• Language: English
• Published: Netherlands Elsevier B.V 01.03.2013
• Subjects: Bleeding; BLOC-3; Blotting, Western; Carrier Proteins - genetics; Carrier Proteins - metabolism; Fluorescent Antibody Technique; Hermanski-Pudlak Syndrome - genetics; Hermanski-Pudlak Syndrome - metabolism; Hermansky–Pudlak syndrome; HPS; Humans; Immunoenzyme Techniques; Immunoprecipitation; Lysosome-related organelle; Membrane Proteins - genetics; Membrane Proteins - metabolism; Mutation - genetics; Oculocutaneous albinism; Proteins - genetics; Proteins - metabolism; Real-Time Polymerase Chain Reaction; Reverse Transcriptase Polymerase Chain Reaction; RNA, Messenger - genetics; BLOC; PAT; IgG; Oculocutaneous albinism; HPS; EGFP; Bleeding; DMEM; Hermansky–Pudlak syndrome; DUF; LAMP-2; FBS; RT-PCR; BLOC-3; NaCl; HA; Lysosome-related organelle
• ISSN: 0167-4889; 0006-3002; 1879-2596
• DOI: 10.1016/j.bbamcr.2012.10.019

Hermansky–Pudlak syndrome (HPS) is a group of rare autosomal recessive disorders characterized by oculocutaneous albinism, a bleeding tendency, and sporadic pulmonary fibrosis, granulomatous colitis or infections. Nine HPS-causing genes have been identified in humans. HPS-1 is the most severe subtype with a prevalence of ~1/1800 in northwest Puerto Rico due to a founder mutation in the HPS1 gene. Mutations in HPS genes affect the biogenesis of lysosome-related organelles such as melanosomes in melanocytes and platelet dense granules. Two of these genes (HPS1 and HPS4) encode the HPS1 and HPS4 proteins, which assemble to form a complex known as Biogenesis of Lysosome-related Organelle Complex 3 (BLOC-3). We report the identification of the interacting regions in HPS1 and HPS4 required for the formation of this complex. Two regions in HPS1, spanning amino acids 1–249 and 506–700 are required for binding to HPS4; the middle portion of HPS1 (residues 250–505) is not required for this interaction. Further interaction studies showed that the N-termini of HPS1 and HPS4 interact with each other and that a discrete region of HPS4 (residues 340–528) interacts with both the N- and C-termini of the HPS1 protein. Several missense mutations found in HPS-1 patients did not affect interaction with HPS4, but some mutations involving regions interacting with HPS4 caused instability of HPS1. These observations extend our understanding of BLOC-3 assembly and represent an important first step in the identification of domains responsible for the biogenesis of lysosome-related organelles. ► An HPS1 isoform encoded by a transcript lacking exon 9 interacts with HPS4 ► The central region of HPS4 protein interacts dually, with either the N- or C-terminus of HPS1 ► Interacting regions of HPS1 and HPS4 exist as soluble and membrane-associated forms ► Missense mutations within interacting regions of HPS1 alter its stability ► Membrane association of HPS1 and HPS4 depends upon specific regions of these proteins