Affinage

NPC2

NPC intracellular cholesterol transporter 2 · UniProt P61916

Length
151 aa
Mass
16.6 kDa
Annotated
2026-06-10
100 papers in source corpus 32 papers cited in narrative 32 extracted findings
Cross-family judge vs UniProt: Affinage preferred faithfulness: 6/6 claims corpus-supported (100%)

Mechanistic narrative

Synthesis pass · prose summary of the discoveries below

NPC2 is a small soluble lysosomal glycoprotein that serves as the primary intraluminal cholesterol carrier, and its deficiency causes Niemann-Pick type C2 disease, with exogenous recombinant NPC2 rescuing lysosomal cholesterol accumulation in patient fibroblasts (PMID:11125141). It binds cholesterol with high affinity in a 1:1 stoichiometry (PMID:10366780), sequestering the sterol in a deep hydrophobic pocket between two β-sheets with only the polar substituent solvent-exposed and aromatic tunnel-entrance residues essential for function (PMID:17573352); binding is selective for cholesterol and closely related sterols over phospholipids, glycolipids, and fatty acids (PMID:17018531). NPC2 extracts cholesterol from internal lysosomal membranes through direct protein-membrane contact, a process accelerated by orders of magnitude by the lysosomal phospholipid LBPA/BMP via a direct interaction at the NPC2 hydrophobic knob, while sphingomyelin inhibits and ceramide promotes transfer (PMID:18823126, PMID:31580258, PMID:20179319). NPC2 then docks onto the middle lumenal domain of NPC1 — an interaction requiring acidic pH and cholesterol-loaded NPC2 — to hand cholesterol through a direct tunnel to NPC1's N-terminal domain for export (PMID:18772377, PMID:22065762, PMID:27551080); mouse double-mutant genetics establishes that NPC1 and NPC2 act non-redundantly in concert in this egress pathway (PMID:15071184). NPC2 reaches lysosomes by mannose-6-phosphate-dependent CI-MPR sorting that depends on TMEM241-supplied UDP-GlcNAc for M6P modification, the GARP complex, and the BORC-ARL8-HOPS ensemble (PMID:37890669, PMID:28658628, PMID:35653304), with Asn-58 glycosylation required for correct targeting (PMID:15542393), and its transcription is directly driven by the non-canonical NF-κB2 pathway (PMID:30091016). Beyond lysosomal egress, secreted NPC2 stimulates ABCG5/G8-dependent biliary cholesterol secretion independently of its lysosomal function (PMID:21315718), supports ovarian steroidogenesis and sperm maturation by providing cholesterol (PMID:19883728, PMID:24709320), and mediates ATRA-induced antimicrobial activity against M. tuberculosis through lysosomal acidification and cholesterol reduction (PMID:24501203).

Mechanistic history

Synthesis pass · year-by-year structured walk · 26 steps
  1. 1999 High

    Before any function was assigned, it was unknown whether NPC2 acted on lipids directly; demonstrating high-affinity 1:1 cholesterol binding established it as a dedicated cholesterol-binding protein.

    Evidence In vitro cholesterol binding assay with purified porcine NPC2 homolog

    PMID:10366780

    Open questions at the time
    • Binding alone did not establish a transport function
    • Did not reveal the structural basis of recognition
  2. 2000 High

    It was unclear whether NPC2 directly mediates cholesterol egress; rescue of LDL-cholesterol accumulation in NPC2-deficient fibroblasts by recombinant protein established NPC2 as causally required for lysosomal cholesterol export and the gene behind NPC2 disease.

    Evidence Fibroblast complementation with recombinant protein, mutation analysis

    PMID:11125141

    Open questions at the time
    • Did not define the molecular partner receiving cholesterol
    • Mechanism of membrane extraction unresolved
  3. 2004 High

    Whether NPC1 and NPC2 act in the same pathway or in parallel was unresolved; identical single- and double-mutant mouse phenotypes provided genetic evidence they function non-redundantly in concert.

    Evidence NPC1;NPC2 double-mutant mouse genetics with biochemical and histopathological readouts

    PMID:15071184

    Open questions at the time
    • Genetic epistasis did not show physical handoff
    • Order and directionality of transfer not established
  4. 2004 High

    The basis of NPC2 lysosomal targeting was unknown; mutagenesis showed glycosylation at Asn-58 specifically directs NPC2 to lysosomes and is required for its trafficking function.

    Evidence Site-directed mutagenesis of glycosylation sites with localization and complementation in NPC2-/- fibroblasts

    PMID:15542393

    Open questions at the time
    • Did not identify the sorting receptor or machinery
    • M6P dependence inferred but not directly demonstrated here
  5. 2006 High

    The breadth of NPC2 ligand specificity and its glycoform heterogeneity were unclear; biochemical profiling defined selective binding to cholesterol and related sterols but not other lipids, and mapped variable N-glycan usage.

    Evidence Mass spectrometry, chromatography-based and fluorescence binding assays, endoglycosidase treatment

    PMID:17018531

    Open questions at the time
    • Did not connect specific glycoforms to function
    • Physiological relevance of each ligand untested
  6. 2007 High

    How NPC2 holds cholesterol was unknown at atomic detail; the crystal structure revealed a deep hydrophobic pocket with conformationally mobile aromatic gate residues essential for function.

    Evidence X-ray crystallography of apo and sterol-bound bovine NPC2

    PMID:17573352

    Open questions at the time
    • Did not show how the sterol enters or exits
    • Structure of the NPC1-bound transfer state not defined
  7. 2008 High

    The receiver of NPC2-bound cholesterol was unknown; reconstitution showed NPC2 accelerates bidirectional transfer between NPC1's NTD and membranes >100-fold and that a cholesterol-binding-deficient mutant fails, placing NPC2 as the essential intermediary in handoff to NPC1.

    Evidence In vitro [3H]cholesterol transfer assay with purified NPC1-NTD, liposomes, and P120S mutant

    PMID:18772377

    Open questions at the time
    • Did not capture the NPC2-NPC1 docking interface
    • Directionality in vivo not established
  8. 2008 High

    How NPC2 engages membranes and what regulates transfer rate was unclear; biophysics demonstrated direct protein-membrane interaction and showed LBPA enhances transfer up to two orders of magnitude.

    Evidence Fluorescence and FTIR spectroscopy, tryptophan spectral shifts, cholesterol transfer assays

    PMID:18823126

    Open questions at the time
    • Did not map the LBPA interaction site
    • Membrane-bound orientation not resolved
  9. 2010 High

    The lipid context governing NPC2 transfer was undefined; defined-liposome assays showed BMP stimulates and sphingomyelin inhibits transfer while ceramide enhances it, with strong selectivity for cholesterol.

    Evidence In vitro liposome cholesterol transfer and membrane fusion assays with defined lipids

    PMID:20179319

    Open questions at the time
    • Did not establish in vivo lipid regulation
    • Membrane fusion role physiological relevance untested
  10. 2011 High

    How NPC2 transfers cargo to NPC1 mechanistically was unknown; SPR and affinity studies showed NPC1's middle lumenal domain binds NPC2 only at acidic pH with cholesterol bound, and disease mutations weaken binding, defining a regulated docking step.

    Evidence Surface plasmon resonance, affinity chromatography, engineered soluble NPC1 domains

    PMID:22065762

    Open questions at the time
    • Did not provide atomic structure of the complex
    • Tunnel for transfer not visualized
  11. 2016 High

    The structural basis of the handoff was unresolved; the NPC1-MLD/NPC2 co-crystal revealed two protruding loops binding NPC2 and a direct cholesterol transfer tunnel between the two binding pockets, supporting the hydrophobic hand-off model.

    Evidence 2.4-Å X-ray crystallography of the complex and docking onto full-length NPC1

    PMID:27551080

    Open questions at the time
    • Static structure did not capture the transfer in motion
    • Membrane-embedded NPC1 export step not resolved
  12. 2014 Medium

    Whether sphingomyelin metabolism gates NPC2 function was unclear; ASM-mediated conversion of sphingomyelin to ceramide was shown to be required for physiological NPC2 cholesterol transfer.

    Evidence Liposomal cholesterol transfer assays with ASM preincubation

    PMID:25339683

    Open questions at the time
    • In vitro only, not independently replicated
    • Cellular consequence of ASM loss on NPC2 not directly tested
  13. 2019 High

    Whether the LBPA stimulation reflects a direct interaction was uncertain; direct binding and domain mapping localized the LBPA interaction to the NPC2 hydrophobic knob and showed LBPA enrichment cannot rescue NPC2-deficient cells, establishing an obligate functional partnership.

    Evidence Direct LBPA-NPC2 binding assay, lipid enrichment of patient fibroblasts, domain-mapping mutagenesis

    PMID:31580258

    Open questions at the time
    • Did not resolve the LBPA-binding structure
    • Stoichiometry of NPC2-LBPA-membrane complex unknown
  14. 2017 Low

    The membrane-engaged conformations of NPC2 were inferred but not modeled; MD simulations defined competing Prone and Supine orientations with BMP specifically favoring the uptake-competent Prone mode.

    Evidence Atomistic molecular dynamics simulations and free energy calculations

    PMID:29084218

    Open questions at the time
    • Computational only, no experimental validation in the same study
    • Predicted orientations not directly observed structurally
  15. 2017 High

    The trafficking machinery delivering NPC2 to lysosomes was undefined; a CRISPR screen identified the GARP complex as required for CI-MPR-dependent NPC2 delivery, linking GARP loss to cholesterol accumulation.

    Evidence Genome-wide CRISPR screen, siRNA validation, transcriptomics, Vps54 mutant mice

    PMID:28658628

    Open questions at the time
    • Did not establish the full sorting receptor cycle
    • Other trafficking regulators not yet identified
  16. 2022 Medium

    Additional regulators of NPC2 lysosomal delivery were unknown; depletion of BORC, ARL8, or HOPS reduced NPC2 lysosomal association and increased its secretion via destabilized CI-MPR, without affecting NPC1.

    Evidence siRNA knockdown, filipin staining, CI-MPR trafficking and cholesterol esterification assays

    PMID:35653304

    Open questions at the time
    • Single lab
    • Direct interactions among components not mapped
  17. 2023 High

    How NPC2 acquires its M6P sorting signal was unresolved; a CRISPR screen identified TMEM241 as the Golgi UDP-GlcNAc transporter required for M6P modification and lysosomal targeting of NPC2.

    Evidence Genome-wide CRISPR-Cas9 screen, M6P modification assay, TMEM241 KO cells and mice

    PMID:37890669

    Open questions at the time
    • Did not test whether other lysosomal enzymes share this dependence specificity
    • Tissue selectivity of the phenotype unexplained
  18. 2018 Medium

    Transcriptional control of NPC2 was unknown; ChIP and loss-of-function across species showed the non-canonical NF-κB2 pathway directly drives NPC2 transcription and that its loss causes cholesterol accumulation.

    Evidence ChIP promoter binding, RNAi, qPCR, NF-κB2-deficient zebrafish and mice

    PMID:30091016

    Open questions at the time
    • Single lab
    • Upstream physiological triggers in tissues not defined
  19. 2006 Medium

    It was unknown whether NPC2 acts outside lysosomes; detection of secreted NPC2 in bile and plasma, enriched in the cholesterol pro-nucleating bile fraction and upregulated in NPC1-null liver, pointed to an extracellular role.

    Evidence Western blotting of bile/plasma fractions, ConA fractionation, NPC1 KO mice

    PMID:16374838

    Open questions at the time
    • Functional role in bile only inferred
    • Mechanism of secretion not defined
  20. 2011 High

    Whether secreted NPC2 functionally affects biliary cholesterol was untested; mouse genetics showed NPC2 stimulates ABCG5/G8-mediated biliary cholesterol efflux, requiring those transporters and independent of its lysosomal function.

    Evidence Adenoviral hepatic knockdown/overexpression, biliary lipid analysis, ABCG5/G8-null mice

    PMID:21315718

    Open questions at the time
    • Molecular interaction between NPC2 and ABCG5/G8 not shown
    • Whether NPC2 delivers cholesterol to the transporters undefined
  21. 2009 Medium

    A physiological role for NPC2 in steroidogenic tissue was unknown; NPC2-deficient female mice showed anovulation, low estradiol, and ovarian cholesterol accumulation, implicating NPC2 in cholesterol export for steroid synthesis.

    Evidence NPC2 KO mice, immunohistochemistry, hormone assays, superovulation

    PMID:19883728

    Open questions at the time
    • Mechanism of cholesterol delivery to steroidogenic machinery not defined
    • Single lab
  22. 2014 Medium

    Whether NPC2 governs sperm cholesterol was unknown; NPC2-/- epididymal sperm showed reduced cholesterol, abnormal capacitation-associated phosphorylation, and impaired fertilization, defining a role in epididymal maturation.

    Evidence NPC2 KO mice, cholesterol quantification, tyrosine phosphorylation Western blot, IVF assay

    PMID:24709320

    Open questions at the time
    • Direct cholesterol transfer to sperm membranes not demonstrated
    • Single lab
  23. 2014 Medium

    A role for NPC2 in innate immunity was unexplored; NPC2 knockdown abolished ATRA-induced cholesterol reduction, lysosomal acidification, and antimicrobial killing of M. tuberculosis.

    Evidence siRNA knockdown, cholesterol and lysosomal acidification assays, intracellular M. tuberculosis killing

    PMID:24501203

    Open questions at the time
    • Mechanism linking cholesterol to acidification and killing not fully defined
    • Single lab
  24. 2015 Medium

    Whether tumor-secreted NPC2 has a signaling role was unknown; NPC2 taken up by immature myeloid cells suppressed CCL6 secretion via lysosomal degradation, restraining CCR1-dependent recruitment to premalignant lung tissue.

    Evidence NPC2 KO/overexpression mouse lung tumor model, ex vivo secretion assays, IMC recruitment in vivo

    PMID:26183450

    Open questions at the time
    • Mechanism of CCL6 degradation control not detailed
    • Generality beyond this model unknown
  25. 2003 Medium

    How NPC1 status affects NPC2 was unclear; fractionation showed NPC1 mutation causes NPC2 to accumulate, become upregulated, and shift toward membrane association in storage organelles.

    Evidence Magnetic chromatography of late endosomes, Western blot, immunofluorescence

    PMID:12554680

    Open questions at the time
    • Did not establish whether membrane shift is cause or consequence
    • Single lab
  26. 2025 Medium

    The cellular lipid and organelle consequences of NPC2 loss beyond cholesterol were unclear; an NPC2-/- model showed accumulation of sphingolipids, reduced mitochondria-lysosome contacts, and swollen acidic compartments without oxidative stress.

    Evidence NPC2-/- HEK cells, lipidomics, contact site quantification, morphology analysis

    PMID:39747180

    Open questions at the time
    • Causal link between cholesterol block and sphingolipid accumulation not dissected
    • Single lab

Open questions

Synthesis pass · forward-looking unresolved questions
  • The mechanism coupling NPC2 cholesterol handling to organelle membrane contact sites and how its diverse extracellular functions are coordinated with its lysosomal role remain open.
  • No structure of the membrane-engaged NPC2 transfer state
  • Mechanism of NPC2-ABCG5/G8 cooperation undefined
  • Integration of innate-immune and reproductive roles with core trafficking unresolved

Mechanism profile

Synthesis pass · controlled-vocabulary classification · explore literature graph →
Molecular activity
GO:0008289 lipid binding 5 GO:0140104 molecular carrier activity 3 GO:0140313 molecular sequestering activity 2
Localization
GO:0005764 lysosome 5 GO:0005576 extracellular region 3 GO:0005768 endosome 3
Pathway
R-HSA-9609507 Protein localization 4 R-HSA-1430728 Metabolism 3 R-HSA-5653656 Vesicle-mediated transport 2
Partners
LBPA/BMPNPC1

Evidence

Reading pass · 32 per-paper findings extracted from the source corpus
Year Finding Method Journal Conf PMIDs
2000 HE1/NPC2 is a ubiquitously expressed lysosomal protein whose deficiency causes Niemann-Pick type C2 disease; exogenous recombinant NPC2 protein ameliorated lysosomal accumulation of LDL-derived cholesterol in NPC2-deficient fibroblasts, establishing its direct role in cholesterol egress from lysosomes. Fibroblast complementation assay with recombinant protein, mutation analysis, Western blot Science High 11125141
1999 The porcine NPC2 homolog (HE1 homolog) specifically binds cholesterol with high affinity (Kd = 2.3 µM) in a 1:1 stoichiometry, establishing NPC2 as a cholesterol-binding protein. In vitro cholesterol binding assay with purified protein, stoichiometry determination Biochimica et biophysica acta High 10366780
2007 Crystal structure of bovine NPC2 bound to cholesterol-3-O-sulfate revealed that the sterol binds in a deep hydrophobic pocket between two β-sheets, with only the sulfate substituent exposed to solvent; two aromatic residues at the tunnel entrance are repositioned upon sterol binding and are essential for NPC2 function. X-ray crystallography (apo and sterol-bound forms), structural analysis The Journal of biological chemistry High 17573352
2008 NPC2 facilitates bidirectional transfer of cholesterol between NPC1 N-terminal domain (NTD) and phosphatidylcholine liposomes; NPC2 accelerates cholesterol transfer between NPC1(NTD) and liposomes >100-fold; the naturally occurring P120S mutant of NPC2 fails to bind cholesterol and fails to stimulate this transfer, establishing NPC2 as an essential intermediary in lysosomal cholesterol handoff to NPC1. In vitro cholesterol transfer assay with [3H]cholesterol, liposomes, and purified recombinant proteins; mutagenesis Proceedings of the National Academy of Sciences of the United States of America High 18772377
2004 Genetic epistasis analysis using NPC1;NPC2 double-mutant mice showed that NPC1 and NPC2 single mutants and double mutants have identical or similar phenotypes in disease onset, pathology, neuronal storage, and lipid biochemistry, providing genetic evidence that NPC1 and NPC2 function in concert (non-redundantly) to facilitate lysosomal lipid egress. Double-mutant mouse genetics, biochemical lipid analysis, histopathology Proceedings of the National Academy of Sciences of the United States of America High 15071184
2011 The second lumenal domain (MLD) of NPC1 binds directly to NPC2, and this interaction is only detected at acidic pH and requires cholesterol to be bound to NPC2, supporting directional cholesterol transfer from NPC2 to NPC1's N-terminal domain. Disease-causing mutations in NPC1 domain 2 decrease NPC2 binding. Surface plasmon resonance, affinity chromatography, engineered soluble NPC1 domain constructs Proceedings of the National Academy of Sciences of the United States of America High 22065762
2016 Crystal structure at 2.4-Å resolution of the human NPC1 middle lumenal domain (MLD) bound to NPC2 carrying cholesterol-3-O-sulfate revealed that NPC1-MLD uses two protruding loops to bind NPC2 (analogous to Ebola virus glycoprotein interaction). Docking onto full-length NPC1 reveals a direct cholesterol transfer tunnel between NPC2 and NPC1 NTD binding pockets, supporting the 'hydrophobic hand-off' model. X-ray crystallography (2.4-Å), structural docking analysis Proceedings of the National Academy of Sciences of the United States of America High 27551080
2006 NPC2 consists of multiple N-glycoforms; mass spectrometry revealed that Asn-19 is not glycosylated, Asn-39 carries Endo H-sensitive oligosaccharide, and Asn-116 is variably utilized. NPC2 binds a range of cholesterol-related molecules (cholesterol precursors, plant sterols, some oxysterols, cholesterol sulfate) but not glycolipids, phospholipids, or fatty acids, and forms an equimolar complex with dehydroergosterol. Mass spectrometry, cation-exchange chromatography-based binding assay, endoglycosidase treatment, fluorescence binding assay The Journal of biological chemistry High 17018531
2004 N-glycosylation at Asn-58 (but not Asn-135) is required for proper lysosomal targeting of NPC2; only the oligosaccharide at Asn-58 is responsible for targeting to lysosomes and is crucial for NPC2 function in restoring normal cholesterol trafficking in NPC2-deficient cells. Site-directed mutagenesis of glycosylation sites, immunocytofluorescence microscopy in NPC2-/- fibroblasts, cholesterol trafficking complementation assay Molecular genetics and metabolism High 15542393
2008 NPC2 transfers cholesterol from membranes to the protein and between membranes via a mechanism involving direct protein-membrane interaction (confirmed by FTIR spectroscopy and tryptophan spectral shifts); the lysosomal phospholipid lyso-bisphosphatidic acid (LBPA) greatly enhances NPC2-mediated cholesterol transfer rates by up to 2 orders of magnitude. Fluorescence spectroscopy cholesterol transfer assay, FTIR spectroscopy, tryptophan fluorescence spectroscopy Biochemistry High 18823126
2019 NPC2 interacts directly with LBPA, and the NPC2 hydrophobic knob domain is the site of this interaction; LBPA enrichment in NPC2-deficient human cells is entirely ineffective at clearing cholesterol (unlike in NPC1-deficient cells), establishing an obligate functional interaction between NPC2 and LBPA in intracellular cholesterol trafficking. Direct binding assay (LBPA-NPC2 interaction), lipid enrichment of patient fibroblasts, domain mapping mutagenesis eLife High 31580258
2010 NPC2 mediates cholesterol transfer between liposomes and stimulates membrane fusion; BMP (bis(monoacylglycero)phosphate) greatly stimulates NPC2-mediated cholesterol transfer, while sphingomyelin inhibits it; ceramide, produced from sphingomyelin hydrolysis, enhances transfer. NPC2 shows specificity for cholesterol over other lipids including ceramide, GM3, phosphatidylethanolamine, and phosphatidylserine. In vitro liposome cholesterol transfer assay with fluorescent/biotinylated vesicles, membrane fusion assay Journal of lipid research High 20179319
2014 Acid sphingomyelinase (ASM)-mediated hydrolysis of sphingomyelin to ceramide in late endosomal membranes is required for physiological NPC2-mediated cholesterol transfer; ASM stimulates NPC2-dependent cholesterol export from the late endosomal compartment. Liposomal cholesterol transfer assay with ASM preincubation, lipid composition manipulation Journal of lipid research Medium 25339683
2017 The GARP complex (containing VPS53) is required for CI-MPR-dependent sorting/trafficking of NPC2 to lysosomes; depletion of GARP subunits impaired NPC2 lysosomal delivery, blocked CI-MPR retrieval to the trans-Golgi network, and caused cholesterol accumulation. Vps54 mutant mice displayed reduced NPC2 protein levels and increased cholesterol accumulation. Genome-wide CRISPR/amphotericin B selection screen, siRNA knockdown, whole-transcriptome sequencing, mouse genetics Cell reports High 28658628
2003 NPC1 governs the endocytic transport of NPC2: NPC1 mutations cause NPC2 to accumulate in and become upregulated in cholesterol-storing late endocytic organelles; a greater proportion of NPC2 becomes membrane-associated in NPC1 mutant late endosomes compared to wild-type. Subcellular fractionation of mouse liver late endosomes by magnetic chromatography, Western blotting, immunofluorescence Human molecular genetics Medium 12554680
2005 NPC2 is present in an incompletely deglycosylated form in NPC1 late endosomes by a mechanism specific to NPC2 (secreted NPC2 from NPC1 cells is normal); a greater proportion of NPC2 partitions with detergent-insoluble late endosomal internal membrane domains in NPC1 vesicles. Magnetic chromatography isolation of late endosomes, Endo H/PNGase F treatment, Western blotting, detergent fractionation The Biochemical journal Medium 15896196
2004 NPC2/HE1 is localized predominantly in neurons (especially pyramidal cells of cerebral cortex, amygdala, and Purkinje cells) and is present in the cytosol of dendrites and on postsynaptic densities (PSD) of neurons, as confirmed by electron microscopic immunocytochemistry and Western blot of PSD-enriched fractions. Immunocytochemistry, electron microscopic immunocytochemistry, subcellular fractionation, Western blotting Neuroscience Medium 15381285
2006 NPC2 is expressed in liver and secreted into bile and plasma; hepatic NPC2 protein expression is dramatically increased in NPC1-deficient mice; biliary NPC2 is exclusively found in the cholesterol pro-nucleating ConA-binding fraction of human bile. Western blotting of bile and plasma fractions, ConA-binding fractionation, NPC1 knockout mouse analysis Hepatology Medium 16374838
2011 Secreted NPC2 stimulates ABCG5/G8-mediated biliary cholesterol efflux but not NPC1L1-mediated cholesterol uptake; hepatic NPC2 overexpression failed to increase biliary cholesterol in ABCG5/G8-null mice, demonstrating that NPC2 requires ABCG5/G8 to stimulate biliary cholesterol secretion. This function was shown to be independent of NPC2's lysosomal cholesterol trafficking function. Adenovirus-mediated hepatic knockdown/overexpression in mice, biliary lipid analysis, in vitro transporter activity assay, ABCG5/G8-null mouse experiment Gastroenterology High 21315718
2017 Atomistic MD simulations identified two competitive membrane binding orientations of NPC2: a 'Prone' mode placing the cholesterol binding pocket in contact with the membrane (associated with cholesterol uptake/release, requires BMP specifically) and a 'Supine' mode with the pocket away from membrane. BMP is specifically required for strong Prone mode binding; sphingomyelin counteracts BMP by hindering Prone mode. Atomistic molecular dynamics simulations, free energy calculations PLoS computational biology Low 29084218
2018 The non-canonical NF-κB pathway (NF-κB2) directly activates NPC2 transcription by binding its promoter; disruption of NF-κB2 or other non-canonical pathway members suppresses NPC2 expression and causes intracellular cholesterol accumulation; LTβR or BaffR stimulation upregulates NPC2 mRNA and protein. RNAi knockdown, promoter binding assay (ChIP), qPCR, cholesterol accumulation assay, NF-κB2-deficient zebrafish embryos and mice Science China. Life sciences Medium 30091016
2023 TMEM241, a Golgi-localized UDP-GlcNAc transporter, is required for mannose-6-phosphate (M6P) modification of NPC2; ablation of TMEM241 impairs M6P-dependent lysosomal targeting of NPC2, causing cholesterol accumulation in lysosomes. Tmem241-deficient mice display cholesterol accumulation in pulmonary cells. Genome-wide CRISPR-Cas9 KO screen (amphotericin B-based), TMEM241 KO cell characterization, M6P modification assay, mouse knockout Journal of lipid research High 37890669
2022 The BORC-ARL8-HOPS ensemble is required for CI-MPR-dependent trafficking of NPC2 to lysosomes; depletion of BORC, ARL8, or HOPS decreases NPC2 lysosomal association, increases NPC2 secretion, increases lysosomal degradation of CI-MPR, and impairs cholesterol egress—without altering NPC1 localization. siRNA knockdown, filipin staining, NPC2 localization by immunofluorescence, CI-MPR trafficking assay, cholesterol esterification assay Molecular biology of the cell Medium 35653304
2009 NPC2 is identified as a binding partner of the C2 domain of human Nedd4L (E3 ubiquitin ligase); NPC2 is expressed along the aldosterone-sensitive distal nephron co-localizing with Nedd4L, and NPC2 transcription/activation is regulated by sodium intake in a salt-sensitive hypertension model, suggesting NPC2 may regulate sodium reabsorption by interacting with the ENaC-Nedd4L system. Yeast two-hybrid screening, co-localization immunohistochemistry, Dahl rat salt-sensitive model Biochemical and biophysical research communications Low 19664597
2014 ATRA-triggered antimicrobial activity against M. tuberculosis requires NPC2 expression; NPC2 knockdown abolishes ATRA-induced decrease in total cellular cholesterol and increase in lysosomal acidification, and ablates ATRA-induced antimicrobial activity against M. tuberculosis. siRNA knockdown, cholesterol quantification, lysosomal acidification assay, intracellular M. tuberculosis killing assay Journal of immunology Medium 24501203
2015 NPC2 secreted from premalignant lung tumour cells is taken up by immature macrophage-lineage cells (IMCs) where it suppresses secretion of CCL6 (at least partly by facilitating its lysosomal degradation), thereby restraining CCR1-dependent IMC recruitment to the tumour microenvironment. NPC2 knockout/overexpression in mouse lung tumor model, ex vivo cell secretion assay, CCL6 measurement, IMC recruitment assay in vivo EMBO molecular medicine Medium 26183450
2009 NPC2-deficient female mice exhibit anovulation, abnormal estrous cycles, and infertility with reduced serum estradiol and accumulated ovarian cholesterol; NPC2 localizes to theca and luteal cells, establishing a role for NPC2 in ovarian cholesterol export for steroid synthesis. NPC2 knockout mouse model, immunohistochemistry, hormone measurements, filipin staining, superovulation experiments Molecular and cellular endocrinology Medium 19883728
2014 Epididymal spermatozoa from NPC2-/- mice have reduced cholesterol content and show defective tyrosine phosphorylation patterns during capacitation and reduced in vitro fertilization ability, establishing NPC2 as a regulator of sperm cholesterol content during epididymal maturation required for fertility. NPC2 knockout mouse model, biochemical cholesterol quantification, flow cytometry, Western blot for tyrosine phosphorylation, in vitro fertilization assay Reproduction, fertility, and development Medium 24709320
2016 NEGR1 interacts with NPC2 and increases its protein stability; ectopic NEGR1 expression relieves abnormal cholesterol accumulation in endosomal compartments; NEGR1-deficient mouse embryonic fibroblasts exhibit increased cholesterol levels and triglyceride contents. Co-immunoprecipitation, cholesterol accumulation assay (filipin staining), NEGR1 knockout MEFs Biochemical and biophysical research communications Low 27940359
2004 NPC2/HE1 secretion from astrocytes is not inhibited by loss of NPC1 function; the majority of sterols secreted from astrocytes are not co-secreted with NPC2 protein, as shown by size-exclusion chromatography with electron microscopy demonstrating separate particles. Size-exclusion chromatography, electron microscopy, Western blot of astrocyte conditioned medium from NPC1-/- and wild-type cells The Journal of biological chemistry Medium 15355983
2025 SARS-CoV-2 ORF3a blocks lysosomal cholesterol egress by binding HOPS subunit VPS39, which traps CI-MPR and retromer in endosomes/lysosomes, impairing NPC2 trafficking to lysosomes; additionally, ORF3a reduces BMP levels by decreasing lysosome-mitochondrion membrane contact sites in a VPS39-dependent manner, identifying VPS39 as a regulator of NPC2 trafficking. Co-immunoprecipitation (ORF3a-VPS39), retromer/CI-MPR localization, NPC2 trafficking assay, lipidomics, proteomics, mitochondria-lysosome contact site quantification, VPS39/retromer deletion experiments bioRxivpreprint Medium 39605369
2025 NPC2 deficiency results in reduced mitochondria-late endosome/lysosome contact sites, accumulation of glucosylsphingosine, glucosylceramides, sphingosine, and sphingomyelins in lysosomes, and swollen lipid-dense acidic compartments—without overt oxidative stress changes. NPC2-/- HEK cell model, mass spectrometry lipidomics, contact site quantification by fluorescence microscopy, organelle morphology analysis Scientific reports Medium 39747180

Source papers

Stage 0 corpus · 100 papers · ranked by NIH iCite citations
Year Title Journal Citations PMID
2000 Identification of HE1 as the second gene of Niemann-Pick C disease. Science (New York, N.Y.) 680 11125141
2008 NPC2 facilitates bidirectional transfer of cholesterol between NPC1 and lipid bilayers, a step in cholesterol egress from lysosomes. Proceedings of the National Academy of Sciences of the United States of America 396 18772377
2004 Genetic evidence for nonredundant functional cooperativity between NPC1 and NPC2 in lipid transport. Proceedings of the National Academy of Sciences of the United States of America 289 15071184
2004 Consequences of NPC1 and NPC2 loss of function in mammalian neurons. Biochimica et biophysica acta 224 15465426
2007 Structural basis of sterol binding by NPC2, a lysosomal protein deficient in Niemann-Pick type C2 disease. The Journal of biological chemistry 176 17573352
2003 NPC1 and NPC2 regulate cellular cholesterol homeostasis through generation of low density lipoprotein cholesterol-derived oxysterols. The Journal of biological chemistry 176 12719428
2009 Niemann-Pick C2 (NPC2) and intracellular cholesterol trafficking. Biochimica et biophysica acta 165 19232397
1999 A porcine homolog of the major secretory protein of human epididymis, HE1, specifically binds cholesterol. Biochimica et biophysica acta 164 10366780
2016 Clues to the mechanism of cholesterol transfer from the structure of NPC1 middle lumenal domain bound to NPC2. Proceedings of the National Academy of Sciences of the United States of America 147 27551080
2011 Niemann-Pick type C 1 function requires lumenal domain residues that mediate cholesterol-dependent NPC2 binding. Proceedings of the National Academy of Sciences of the United States of America 128 22065762
2001 Niemann-Pick disease type C: spectrum of HE1 mutations and genotype/phenotype correlations in the NPC2 group. American journal of human genetics 125 11567215
1996 Molecular cloning and characterization of HE1, a major secretory protein of the human epididymis. Biology of reproduction 113 8924505
2004 Structure and function of the NPC2 protein. Biochimica et biophysica acta 100 15465422
2006 NPC2, the protein deficient in Niemann-Pick C2 disease, consists of multiple glycoforms that bind a variety of sterols. The Journal of biological chemistry 96 17018531
2014 All-trans retinoic acid-triggered antimicrobial activity against Mycobacterium tuberculosis is dependent on NPC2. Journal of immunology (Baltimore, Md. : 1950) 90 24501203
2003 Defective endocytic trafficking of NPC1 and NPC2 underlying infantile Niemann-Pick type C disease. Human molecular genetics 81 12554680
2008 Regulation of sterol transport between membranes and NPC2. Biochemistry 77 18823126
2012 Drosophila melanogaster NPC2 proteins bind bacterial cell wall components and may function in immune signal pathways. Insect biochemistry and molecular biology 76 22580186
2014 Acid sphingomyelinase activity is regulated by membrane lipids and facilitates cholesterol transfer by NPC2. Journal of lipid research 72 25339683
2019 Intracellular cholesterol trafficking is dependent upon NPC2 interaction with lysobisphosphatidic acid. eLife 66 31580258
2010 Role of endosomal membrane lipids and NPC2 in cholesterol transfer and membrane fusion. Journal of lipid research 66 20179319
2005 Niemann-Pick C disease: use of denaturing high performance liquid chromatography for the detection of NPC1 and NPC2 genetic variations and impact on management of patients and families. Molecular genetics and metabolism 66 16126423
2007 Niemann-Pick C disease: functional characterization of three NPC2 mutations and clinical and molecular update on patients with NPC2. Clinical genetics 52 17470133
2004 Niemann-Pick type C disease: importance of N-glycosylation sites for function and cellular location of the NPC2 protein. Molecular genetics and metabolism 52 15542393
2006 NPC2 is expressed in human and murine liver and secreted into bile: potential implications for body cholesterol homeostasis. Hepatology (Baltimore, Md.) 51 16374838
2002 Frontal lobe atrophy due to a mutation in the cholesterol binding protein HE1/NPC2. Annals of neurology 51 12447927
2005 NPC1 late endosomes contain elevated levels of non-esterified ('free') fatty acids and an abnormally glycosylated form of the NPC2 protein. The Biochemical journal 50 15896196
2011 NPC2 regulates biliary cholesterol secretion via stimulation of ABCG5/G8-mediated cholesterol transport. Gastroenterology 46 21315718
2017 The GARP Complex Is Involved in Intracellular Cholesterol Transport via Targeting NPC2 to Lysosomes. Cell reports 44 28658628
2001 Cholesterol overload promotes morphogenesis of a Niemann-Pick C (NPC)-like compartment independent of inhibition of NPC1 or HE1/NPC2 function. The Journal of biological chemistry 42 11571306
2017 FTY720/fingolimod increases NPC1 and NPC2 expression and reduces cholesterol and sphingolipid accumulation in Niemann-Pick type C mutant fibroblasts. FASEB journal : official publication of the Federation of American Societies for Experimental Biology 41 28082351
2004 Secretion of sterols and the NPC2 protein from primary astrocytes. The Journal of biological chemistry 41 15355983
2016 Transcriptomic Biomarkers for Tuberculosis: Evaluation of DOCK9. EPHA4, and NPC2 mRNA Expression in Peripheral Blood. Frontiers in microbiology 40 27826286
2019 Sterol transfer by atypical cholesterol-binding NPC2 proteins in coral-algal symbiosis. eLife 38 31159921
2011 Regulation of the NPC2 protein-mediated cholesterol trafficking by membrane lipids. Journal of neurochemistry 38 21214551
2016 Structure of glycosylated NPC1 luminal domain C reveals insights into NPC2 and Ebola virus interactions. FEBS letters 37 26846330
2009 Molecular analysis of NPC1 and NPC2 gene in 34 Niemann-Pick C Italian patients: identification and structural modeling of novel mutations. Neurogenetics 37 19252935
2016 The new obesity-associated protein, neuronal growth regulator 1 (NEGR1), is implicated in Niemann-Pick disease Type C (NPC2)-mediated cholesterol trafficking. Biochemical and biophysical research communications 36 27940359
2013 Involvement of cathepsins B and L in inflammation and cholesterol trafficking protein NPC2 secretion in macrophages. Obesity (Silver Spring, Md.) 36 23666609
2014 Diagnosis of Niemann-Pick disease type C with 7-ketocholesterol screening followed by NPC1/NPC2 gene mutation confirmation in Chinese patients. Orphanet journal of rare diseases 35 24915861
2011 Sterol transfer between cyclodextrin and membranes: similar but not identical mechanism to NPC2-mediated cholesterol transfer. Biochemistry 35 21740003
2013 Pulmonary abnormalities in animal models due to Niemann-Pick type C1 (NPC1) or C2 (NPC2) disease. PloS one 34 23843985
2006 HE1/NPC2 status in human reproductive tract and ejaculated spermatozoa: consequence of vasectomy. Molecular human reproduction 31 16772431
2019 The characteristics and biological significance of NPC2: Mutation and disease. Mutation research. Reviews in mutation research 29 31843136
2007 Do mammalian NPC1 and NPC2 play a role in intestinal cholesterol absorption? The Biochemical journal 29 17880278
2019 Insights into the Molecular Mechanisms of Cholesterol Binding to the NPC1 and NPC2 Proteins. Advances in experimental medicine and biology 27 31098815
2015 The cholesterol-binding protein NPC2 restrains recruitment of stromal macrophage-lineage cells to early-stage lung tumours. EMBO molecular medicine 27 26183450
2014 Spermatozoa from mice deficient in Niemann-Pick disease type C2 (NPC2) protein have defective cholesterol content and reduced in vitro fertilising ability. Reproduction, fertility, and development 27 24709320
2013 Computational studies of the cholesterol transport between NPC2 and the N-terminal domain of NPC1 (NPC1(NTD)). Biochemistry 27 24001314
2017 Expression patterns of sterol transporters NPC1 and NPC2 in the cnidarian-dinoflagellate symbiosis. Cellular microbiology 26 28544363
2017 Relationship between HSP90a, NPC2 and L-PGDS proteins to boar semen freezability. Journal of animal science and biotechnology 25 28270911
2004 Neuronal localization and association of Niemann Pick C2 protein (HE1/NPC2) with the postsynaptic density. Neuroscience 24 15381285
2017 Concerted regulation of npc2 binding to endosomal/lysosomal membranes by bis(monoacylglycero)phosphate and sphingomyelin. PLoS computational biology 23 29084218
2005 Niemann-Pick type C disease: subcellular location and functional characterization of NPC2 proteins with naturally occurring missense mutations. Human mutation 23 15937921
2004 Vasectomy influences expression of HE1 but not HE2 and HE5 genes in human epididymis. Journal of andrology 23 14662784
2017 Pulmonary manifestations in Niemann-Pick type C disease with mutations in NPC2 gene: case report and review of literature. BMC medical genetics 21 28095804
2018 Attenuation of the Niemann-Pick type C2 disease phenotype by intracisternal administration of an AAVrh.10 vector expressing Npc2. Experimental neurology 18 29655638
2016 The NPC2 protein: A novel dog allergen. Annals of allergy, asthma & immunology : official publication of the American College of Allergy, Asthma, & Immunology 18 26995145
2018 The non-canonical NF-κB pathway promotes NPC2 expression and regulates intracellular cholesterol trafficking. Science China. Life sciences 16 30091016
2009 Female infertility due to anovulation and defective steroidogenesis in NPC2 deficient mice. Molecular and cellular endocrinology 16 19883728
2021 Secretory NPC2 Protein-Mediated Free Cholesterol Levels Were Correlated with the Sorafenib Response in Hepatocellular Carcinoma. International journal of molecular sciences 15 34445279
2022 BORC-ARL8-HOPS ensemble is required for lysosomal cholesterol egress through NPC2. Molecular biology of the cell 14 35653304
2021 npc2-Deficient Zebrafish Reproduce Neurological and Inflammatory Symptoms of Niemann-Pick Type C Disease. Frontiers in cellular neuroscience 14 33986646
2019 Relative content of Niemann-Pick C2 protein (NPC2) in seminal plasma, but not that of spermadhesin AQN-1, is related to boar sperm cryotolerance. Theriogenology 14 31711697
2014 Niemann-Pick type C disease: a QM/MM study of conformational changes in cholesterol in the NPC1(NTD) and NPC2 binding pockets. Biochemistry 14 25251378
2013 Identification of mutation in NPC2 by exome sequencing results in diagnosis of Niemann-Pick disease type C. Molecular genetics and metabolism 14 23791309
2023 Niemann-Pick Disease Type C (NPDC) by Mutation of NPC1 and NPC2: Aberrant Lysosomal Cholesterol Trafficking and Oxidative Stress. Antioxidants (Basel, Switzerland) 13 38136141
2022 Retinoic acid restores the levels of cellular cholesterol in Leishmania donovani infected macrophages by increasing npc1 and npc2 expressions. Biochimie 13 35272007
2021 Cat-NPC2, a Newly Identified Allergen, With High Cross-Reactivity to Can f 7. Allergy, asthma & immunology research 13 33191681
2021 Niemann-Pick Type C 1 (NPC1) and NPC2 Gene Variability in Demented Patients with Evidence of Brain Amyloid Deposition. Journal of Alzheimer's disease : JAD 13 34420959
2022 Effects of Niemann-Pick type C2 (NPC2) gene transcripts silencing on behavior of Varroa destructor and molecular changes in the putative olfactory gene networks. Insect biochemistry and molecular biology 10 35926690
2009 Identification of NPC2 protein as interaction molecule with C2 domain of human Nedd4L. Biochemical and biophysical research communications 10 19664597
2018 Simulations of NPC1(NTD):NPC2 Protein Complex Reveal Cholesterol Transfer Pathways. International journal of molecular sciences 9 30181526
2014 Characterization of a spontaneous novel mutation in the NPC2 gene in a cat affected by Niemann Pick type C disease. PloS one 9 25396745
2009 Physiological and coordinate downregulation of the NPC1 and NPC2 genes are associated with the sequestration of LDL-derived cholesterol within endocytic compartments. Journal of cellular biochemistry 9 19746448
2005 [Fatal neonatal respiratory distress in Niemann-Pick C2 and prenatal diagnosis with mutations in gene HE1/NPC2]. Archives de pediatrie : organe officiel de la Societe francaise de pediatrie 9 15808435
2021 Transcriptomic Biomarkers for Tuberculosis: Validation of NPC2 as a Single mRNA Biomarker to Diagnose TB, Predict Disease Progression, and Monitor Treatment Response. Cells 8 34685683
2014 Effect of the replacement of aspartic acid/glutamic acid residues with asparagine/glutamine residues in RNase He1 from Hericium erinaceus on inhibition of human leukemia cell line proliferation. Bioscience, biotechnology, and biochemistry 7 25338779
2007 A role for NPC1 and NPC2 in intestinal cholesterol absorption--the hypothesis gutted. The Biochemical journal 7 17956226
2025 Deficiency in NPC2 results in disruption of mitochondria-late endosome/lysosomes contact sites and endo-lysosomal lipid dyshomeostasis. Scientific reports 6 39747180
2023 Exploration of NPC2 as a Potential Biomarker for Immunotherapy Using RNA-seq and Protein Data - A New Hypothesis. Endocrine, metabolic & immune disorders drug targets 6 37056065
2023 The Npc2Gt(LST105)BygNya mouse signifies pathological changes comparable to human Niemann-Pick type C2 disease. Molecular and cellular neurosciences 6 37454976
2024 Low expression of lysosome-related genes KCNE1, NPC2, and SFTPD promote cancer cell proliferation and tumor associated M2 macrophage polarization in lung adenocarcinoma. Heliyon 5 38509982
2023 TMEM241 is a UDP-N-acetylglucosamine transporter required for M6P modification of NPC2 and cholesterol transport. Journal of lipid research 5 37890669
2021 Pathophysiological In Vitro Profile of Neuronal Differentiated Cells Derived from Niemann-Pick Disease Type C2 Patient-Specific iPSCs Carrying the NPC2 Mutations c.58G>T/c.140G>T. International journal of molecular sciences 4 33924575
2021 Identification and Classification of Rare Variants in NPC1 and NPC2 in Quebec. Scientific reports 4 33990640
2009 Getting a "Hold" on NPC2. Cell metabolism 4 19723490
2025 SARS-CoV-2 ORF3a blocks lysosomal cholesterol egress by disrupting VPS39-regulated NPC2 trafficking and BMP metabolism. bioRxiv : the preprint server for biology 3 39605369
2024 NPC2, a seminal plasma protein with membrane cholesterol-binding ability, influences the cryotolerance and functionality of spermatozoa from Chino Santandereano bulls. Animal reproduction science 3 39798440
2023 Focusing on the Abnormal Events of NPC1, NPC2, and NPC1L1 in Pan-Cancer and Further Constructing LUAD and KICH Prediction Models. Journal of proteome research 3 38109854
2025 Genome-Wide Identification, Gene Duplication, and Expression Pattern of NPC2 Gene Family in Parnassius glacialis. Genes 2 40149401
2025 ALKBH5-mediated NPC2 mRNA m6A demethylation promotes resistance to oxaliplatin in colorectal cancer. Functional & integrative genomics 2 40681956
2023 Novel Mutation in the Feline NPC2 Gene in Cats with Niemann-Pick Disease. Animals : an open access journal from MDPI 2 37458497
2021 NPC2 expression in thyroid tumors and its possible diagnostic utility. International journal of clinical and experimental pathology 2 33532030
2020 Existence and distribution of Niemann-Pick type 2C (NPC2) in prawn reproductive tract and its putative role as a cholesterol modulator during sperm transit in the vas deferens. Cell and tissue research 2 32556727
2010 Proteomic identification and characterization of secreted N-glycosylated NPC2 following cross-linking of the high-affinity receptor for IgE on mast cells. Cell biology international 2 20001954
2026 Transport of sphingolipids by yeast Npc2 supports phase separation of the vacuole membrane. The Journal of biological chemistry 1 41850403
2025 Interaction between expression of CD23 on B-lymphocytes and level of specific IgE against molecular components of NPC2 family, lipocalins, uteroglobins, and molecular components of molds and yeast. Journal of immunotoxicology 1 40785403
2019 X-Ray Crystallographic Structure of Hericium erinaceus Ribonuclease, RNase He1 in Complex with Zinc. Biological & pharmaceutical bulletin 1 31787719
2014 Mutagenesis of the novel Hericium erinaceus ribonuclease, RNase He1, reveals critical responsible residues for enzyme stability and activity. Biological & pharmaceutical bulletin 1 25366489

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