Affinage

HPS1

BLOC-3 complex member HPS1 · UniProt Q92902

Length
700 aa
Mass
79.3 kDa
Annotated
2026-06-10
31 papers in source corpus 10 papers cited in narrative 12 extracted findings
Cross-family judge vs UniProt: Affinage preferred faithfulness: 7/7 claims corpus-supported (100%)

Mechanistic narrative

Synthesis pass · prose summary of the discoveries below

HPS1 is a subunit of BLOC-3, a stable cytosolic complex it forms with HPS4 that governs the biogenesis and intracellular positioning of lysosome-related organelles (PMID:12756248, PMID:12847290, PMID:12663659). HPS1 and HPS4 assemble through a divalent interaction interface in which two distinct regions of HPS1 (residues 1–249 and 506–700) each contact HPS4, with the central region dispensable (PMID:23103514); this assembly depends on the C-terminal region of HPS1, and the disease-associated L668P variant abolishes incorporation into BLOC-3 (PMID:16185271). Within the complex, HPS4 is required to stabilize HPS1 protein, and the two do not interact directly in yeast two-hybrid, indicating that complex formation requires additional cellular context (PMID:12663659). Functionally, BLOC-3/HPS1 regulates the juxtanuclear positioning of lysosomes and late endosomes (PMID:12847290) and directs proper trafficking of the melanogenic enzymes tyrosinase and TYRP1 to melanosomes, such that HPS1 loss mistranslocates these enzymes into aberrant granular complexes and reduces melanin synthesis (PMID:11564171). HPS1 functions largely independently of, but partially epistatic to, the AP-3 (HPS2) and BLOC-1 pathways for melanosome, lysosome, and dense-granule biogenesis (PMID:12847290, PMID:11861280). The role of HPS1 extends to regulated secretion: in Paneth cells it controls VAMP7 removal during maturation of large dense core vesicles and is required for proper lysozyme secretion, with loss altering intestinal microbiota (PMID:33224134). Across vertebrates, HPS1 has a conserved requirement in pigmentation and in blood clotting/platelet (thrombocyte) function (PMID:35944207), and in skin it has a developmental role in interfollicular melanocyte maturation distinct from its melanosome-biogenesis function (PMID:17068483).

Mechanistic history

Synthesis pass · year-by-year structured walk · 8 steps
  1. 2002 Medium

    Established that HPS1 occupies a pathway position distinct from the AP-3 (HPS2) machinery, framing organelle biogenesis as the convergence of multiple independent routes.

    Evidence Genetic epistasis in doubly homozygous mutant mice with EM and lysosomal enzyme/serotonin readouts

    PMID:11861280

    Open questions at the time
    • Did not identify the molecular complex through which HPS1 acts
    • Mechanism of pathway independence at the trafficking step unresolved
  2. 2001 Medium

    Connected HPS1 directly to melanosome cargo delivery by showing it is required to route tyrosinase and TYRP1 to melanosomes.

    Evidence Antisense knockdown with tyrosinase activity assays, immunofluorescence, and EM

    PMID:11564171

    Open questions at the time
    • Did not define how HPS1 controls cargo sorting molecularly
    • No partner protein identified
  3. 2003 High

    Defined the molecular identity of HPS1's functional unit as the HPS1–HPS4 BLOC-3 complex and showed it regulates lysosome/late endosome positioning.

    Evidence Reciprocal Co-IP of endogenous and tagged proteins with size exclusion and sedimentation analysis; fluorescence microscopy of mutant fibroblasts; protein stability blots; epistasis with BLOC-1 in double-mutant mice; subcellular fractionation

    PMID:11861280 PMID:12663659 PMID:12756248 PMID:12847290

    Open questions at the time
    • HPS1 and HPS4 did not interact directly in yeast two-hybrid, leaving the requirement for additional factors unexplained
    • Higher-order ~500 kDa and BLOC-5 assemblies not functionally characterized
    • Catalytic activity of the complex not yet defined
  4. 2005 Medium

    Linked a human disease variant to loss of BLOC-3 assembly, showing the C-terminus of HPS1 is essential for complex formation.

    Evidence Transfection of the L668P HPS1 variant into Hps1-deficient melanocytes with BLOC-3 assembly assay

    PMID:16185271

    Open questions at the time
    • Did not map the precise interaction residues
    • No structural model of the interface
  5. 2006 Medium

    Distinguished a developmental role of HPS1 in interfollicular melanocyte maturation from its core melanosome-biogenesis function.

    Evidence Tyrosinase activity assays, melanocyte counting, and EM in pale ear (Hps1-mutant) mouse skin

    PMID:17068483

    Open questions at the time
    • Mechanistic basis of the tissue-specific (tail vs dorsal) difference unresolved
  6. 2012 Medium

    Resolved the architecture of BLOC-3 assembly as a divalent HPS1–HPS4 interface engaging both termini of HPS1.

    Evidence Co-IP of truncation and missense mutants of HPS1 and HPS4

    PMID:23103514

    Open questions at the time
    • No structural validation of the mapped interface
    • Does not establish the complex's enzymatic output
  7. 2020 Medium

    Extended HPS1/BLOC-3 function to regulated secretion, implicating it in VAMP7 removal during dense core vesicle maturation and in mucosal homeostasis.

    Evidence EM, lysozyme secretion assays, VAMP7 immunofluorescence, and 16S microbiota sequencing in Hps1-deficient mouse Paneth cells

    PMID:33224134

    Open questions at the time
    • Rab32/38 GEF activity stated but biochemical GEF assay details not provided
    • Direct mechanism of VAMP7 removal not reconstituted
  8. 2022 Medium

    Demonstrated evolutionary conservation of HPS1 function in pigmentation and clotting beyond mammals.

    Evidence Positional cloning and phenotypic analysis of hps1 mutant medaka (melanophore pigmentation and coagulation)

    PMID:35944207

    Open questions at the time
    • Did not test whether the fish complex retains the mammalian GEF mechanism
    • Thrombocyte organelle defect not resolved at molecular level

Open questions

Synthesis pass · forward-looking unresolved questions
  • How BLOC-3 enzymatic activity (GEF for Rab32/38) is coupled to specific cargo sorting events and how it is recruited to maturing organelles remain to be defined.
  • No reconstituted GEF assay in the corpus
  • No structural model of BLOC-3
  • Recruitment determinants to organelle membranes unknown

Mechanism profile

Synthesis pass · controlled-vocabulary classification · explore literature graph →
Molecular activity
GO:0060090 molecular adaptor activity 2 GO:0098772 molecular function regulator activity 1
Localization
GO:0005829 cytosol 2 GO:0005764 lysosome 1 GO:0005768 endosome 1
Pathway
R-HSA-1852241 Organelle biogenesis and maintenance 2 R-HSA-5653656 Vesicle-mediated transport 2 R-HSA-9609507 Protein localization 2
Partners
HPS4
Complex memberships
BLOC-3

Evidence

Reading pass · 12 per-paper findings extracted from the source corpus
Year Finding Method Journal Conf PMIDs
2003 HPS1 and HPS4 proteins form a stable cytosolic complex termed BLOC-3 (biogenesis of lysosome-related organelles complex 3), as demonstrated by co-immunoprecipitation of both epitope-tagged and endogenous proteins; the complex has an apparent molecular mass of ~175 kDa by size exclusion chromatography and sedimentation velocity analysis. Co-immunoprecipitation, size exclusion chromatography, sedimentation velocity analysis The Journal of biological chemistry High 12663659 12756248 12847290
2003 Loss of HPS1 or HPS4 (BLOC-3 subunits) causes abnormal localization of lysosomes and late endosomes, which are less concentrated at the juxtanuclear region in mutant cells than in control fibroblasts, establishing BLOC-3 as a regulator of intracellular lysosome/late endosome positioning. Fluorescence microscopy of mutant fibroblasts deficient in HPS1 or HPS4 Proceedings of the National Academy of Sciences of the United States of America Medium 12847290
2003 Double-mutant mice deficient in both BLOC-3 (HPS1) and BLOC-1 (pallidin) subunits show a coat-color phenotype indistinguishable from BLOC-1 single mutants, placing BLOC-3 in a BLOC-1-dependent pathway for melanosome biogenesis by genetic epistasis. Genetic epistasis using homozygous double-mutant mice Proceedings of the National Academy of Sciences of the United States of America Medium 12847290
2003 HPS4 protein is required for the stability of HPS1; cells from HPS4-deficient (light ear) mice also lack HPS1 protein, indicating HPS4 stabilizes HPS1 within the BLOC-3 complex. HPS1 and HPS4 do not interact directly in yeast two-hybrid, suggesting the interaction requires additional factors or context. Western blotting of mutant mouse cells, yeast two-hybrid assay The Journal of biological chemistry Medium 12663659
2003 In a partially purified vesicular/organellar fraction, HPS1 and HPS4 are both components of a larger ~500 kDa complex termed BLOC-3, within which HPS1 and HPS4 form a discrete ~200 kDa module (BLOC-4). In the cytosol, HPS1 (but not HPS4) is part of yet another complex termed BLOC-5. Sedimentation/size-fractionation of subcellular fractions, Western blotting The Journal of biological chemistry Medium 12663659
2002 HPS1 (pale ear) and HPS2 (pearl/AP-3) genes function largely independently to regulate melanosome, lysosome, and platelet dense granule biogenesis; doubly homozygous mutant mice show additive/synergistic organelle defects including increased lysosomal enzyme levels in lung, suggesting independent pathway positions. Genetic epistasis using doubly homozygous mutant mice; electron microscopy, biochemical assays of lysosomal enzymes and serotonin Blood Medium 11861280
2001 Loss of HPS1 protein expression (via antisense transfection) causes mistranslocation of tyrosinase and tyrosinase-related protein 1 (TYRP1) to large granular complexes rather than melanosomes, reducing melanin synthesis; tyrosinase activity in intact cells (but not cell lysates) is significantly decreased, indicating HPS1 is required for proper trafficking of melanogenic enzymes to melanosomes. Antisense cDNA transfection, Western blotting, intact-cell and lysate tyrosinase activity assays, immunofluorescence, electron microscopy The Journal of investigative dermatology Medium 11564171
2005 The HPS1 missense variant L668P, found in a Japanese HPS patient, produces an HPS1 protein that is unable to assemble into BLOC-3, as demonstrated by transfection into Hps1-mutant melanocytes, establishing that the C-terminal region of HPS1 is required for BLOC-3 assembly. Transfection of mutant HPS1 into Hps1-deficient mouse melanocytes, co-immunoprecipitation/functional assay of BLOC-3 assembly The Journal of investigative dermatology Medium 16185271
2012 Two distinct regions of HPS1 (amino acids 1–249 and 506–700) are each required for binding to HPS4; the middle portion (residues 250–505) is dispensable. The N-termini of HPS1 and HPS4 interact with each other, and a discrete region of HPS4 (residues 340–528) interacts with both the N- and C-termini of HPS1, constituting a divalent interaction interface required for BLOC-3 formation. Co-immunoprecipitation of truncation and missense mutants of HPS1 and HPS4 Biochimica et biophysica acta Medium 23103514
2020 HPS1 (as a BLOC-3 subunit acting as a guanine nucleotide exchange factor for Rab32/38) plays a role in removing VAMP7 from maturing large dense core vesicles (LDCVs) in Paneth cells; loss of HPS1 in pale ear mice causes increased number and enlarged size of LDCVs and impairs regulated lysozyme secretion, leading to altered intestinal microbiota composition. Electron microscopy of Paneth cells in Hps1-deficient mice, lysozyme secretion assays, VAMP7 localization by immunofluorescence, microbiota 16S sequencing Frontiers in immunology Medium 33224134
2006 In the pale ear (Hps1-mutant) mouse, HPS1 deficiency causes delayed onset of tyrosinase activity, decreased numbers of interfollicular epidermal and dermal melanocytes, and severe immaturity of epidermal melanosomes specifically in tail skin, but not in dorsal follicular melanocytes, demonstrating a developmental role of HPS1 in interfollicular melanocyte function distinct from its role in melanosome biogenesis. Tyrosinase activity assays, cell counting, electron microscopy of melanosomes in Hps1-mutant mice The Journal of investigative dermatology Medium 17068483
2022 Hps1-deficient medaka fish (identified by positional cloning) exhibit absence of melanophore pigmentation and reduced blood coagulation, demonstrating an evolutionarily conserved role of hps1 in melanin production and blood clotting (via thrombocytes in fish, analogous to platelets in mammals). Positional cloning, phenotypic analysis of hps1 mutant medaka (pigmentation and coagulation assays) G3 (Bethesda, Md.) Medium 35944207

Source papers

Stage 0 corpus · 31 papers · ranked by NIH iCite citations
Year Title Journal Citations PMID
2000 Pulmonary function and high-resolution CT findings in patients with an inherited form of pulmonary fibrosis, Hermansky-Pudlak syndrome, due to mutations in HPS-1. Chest 133 10631210
2003 Biogenesis of lysosome-related organelles complex 3 (BLOC-3): a complex containing the Hermansky-Pudlak syndrome (HPS) proteins HPS1 and HPS4. Proceedings of the National Academy of Sciences of the United States of America 107 12847290
2003 BLOC-3, a protein complex containing the Hermansky-Pudlak syndrome gene products HPS1 and HPS4. The Journal of biological chemistry 103 12756248
2003 The Hermansky-Pudlak syndrome 1 (HPS1) and HPS4 proteins are components of two complexes, BLOC-3 and BLOC-4, involved in the biogenesis of lysosome-related organelles. The Journal of biological chemistry 87 12663659
2002 The Hermansky-Pudlak syndrome 1 (HPS1) and HPS2 genes independently contribute to the production and function of platelet dense granules, melanosomes, and lysosomes. Blood 51 11861280
2005 High frequency of Hermansky-Pudlak syndrome type 1 (HPS1) among Japanese albinism patients and functional analysis of HPS1 mutant protein. The Journal of investigative dermatology 44 16185271
1999 Dermatologic manifestations of Hermansky-Pudlak syndrome in patients with and without a 16-base pair duplication in the HPS1 gene. Archives of dermatology 39 10411151
2012 A divalent interaction between HPS1 and HPS4 is required for the formation of the biogenesis of lysosome-related organelle complex-3 (BLOC-3). Biochimica et biophysica acta 33 23103514
2000 Correlation of visual acuity and ocular pigmentation with the 16-bp duplication in the HPS-1 gene of Hermansky-Pudlak syndrome, a form of albinism. Ophthalmology 26 10768343
2014 Hermansky-Pudlak syndrome. Overview of clinical and molecular features and case report of a new HPS-1 variant. Hamostaseologie 24 25117010
2000 Heterozygous HPS1 mutations in a case of Hermansky-Pudlak syndrome with giant melanosomes. The British journal of dermatology 21 10971344
2006 Hermansky-Pudlak HPS1/pale ear gene regulates epidermal and dermal melanocyte development. The Journal of investigative dermatology 19 17068483
2001 Abnormal translocation of tyrosinase and tyrosinase-related protein 1 in cutaneous melanocytes of Hermansky-Pudlak Syndrome and in melanoma cells transfected with anti-sense HPS1 cDNA. The Journal of investigative dermatology 18 11564171
2011 The total synthesis of a ganglioside Hp-s1 analogue possessing neuritogenic activity by chemoselective activation glycosylation. Organic & biomolecular chemistry 17 22179062
2011 Novel mutations in the HPS1 gene among Puerto Rican patients. Clinical genetics 14 20662851
2020 Hp-s1 Ganglioside Suppresses Proinflammatory Responses by Inhibiting MyD88-Dependent NF-κB and JNK/p38 MAPK Pathways in Lipopolysaccharide-Stimulated Microglial Cells. Marine drugs 12 33003399
2018 Ganglioside Hp-s1 Analogue Inhibits Amyloidogenic Toxicity in Alzheimer's Disease Model Cells. ACS chemical neuroscience 12 30346715
2020 HPS1 Regulates the Maturation of Large Dense Core Vesicles and Lysozyme Secretion in Paneth Cells. Frontiers in immunology 11 33224134
2019 Novel genetic variant of HPS1 gene in Hermansky-Pudlak syndrome with fulminant progression of pulmonary fibrosis: a case report. BMC pulmonary medicine 9 31619213
2010 Compound heterozygous mutations in 2 siblings with Hermansky-Pudlak syndrome type 1 (HPS1). Klinische Padiatrie 8 20514622
2014 The Ap3b1 gene regulates the ocular melanosome biogenesis and tyrosinase distribution differently from the Hps1 gene. Experimental eye research 7 25160823
2019 Different functions of biogenesis of lysosomal organelles complex 3 subunit 1 (Hps1) and adaptor-related protein complex 3, beta 1 subunit (Ap3b1) genes on spermatogenesis and male fertility. Reproduction, fertility, and development 6 30786955
2022 Delineating Novel and Known Pathogenic Variants in TYR, OCA2 and HPS-1 Genes in Eight Oculocutaneous Albinism (OCA) Pakistani Families. Genes 5 35328057
2018 Hermansky-Pudlak syndrome with a novel genetic variant in HPS1 and subsequent accelerated pulmonary fibrosis: significance for phenocopy diseases. Thorax 5 29941477
2016 Generation of Hermansky-Pudlak Syndrome Type 1 (HPS1) induced pluripotent stem cells (iPSCs). Stem cell research 5 27345974
2004 Mutation analysis of HPS1, the gene mutated in Hermansky-Pudlak syndrome, in patients with isolated platelet dense-granule deficiency. Haematologica 5 15020272
2000 Characterization of a partial pseudogene homologous to the Hermansky-Pudlak syndrome gene HPS-1; relevance for mutation detection. Human genetics 5 10798370
2021 Hermansky-Pudlak syndrome: Five Chinese patients with novel variants in HPS1 and HPS6. European journal of medical genetics 3 33878481
2018 Synthesis and Bioassay of Neurogenically Potent Gangliosides DSG-A, Hp-s1 and Their Analogues. ACS chemical neuroscience 3 29558805
2022 Evolutionarily conserved role of hps1 in melanin production and blood coagulation in medaka fish. G3 (Bethesda, Md.) 1 35944207
2022 Compound Homozygous Rare Mutations in PLCE1 and HPS1 Genes Associated with Autosomal Recessive Retinitis Pigmentosa in Pakistani Families. Iranian journal of public health 1 36743378

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