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Structural highlights

Disease

[NPC1_HUMAN] Defects in NPC1 are the cause of Niemann-Pick disease type C1 (NPC1) [MIM:257220]. A lysosomal storage disorder that affects the viscera and the central nervous system. It is due to defective intracellular processing and transport of low-density lipoprotein derived cholesterol. It causes accumulation of cholesterol in lysosomes, with delayed induction of cholesterol homeostatic reactions. Niemann-Pick disease type C1 has a highly variable clinical phenotype. Clinical features include variable hepatosplenomegaly and severe progressive neurological dysfunction such as ataxia, dystonia and dementia. The age of onset can vary from infancy to late adulthood. An allelic variant of Niemann-Pick disease type C1 is found in people with Nova Scotia ancestry. Patients with the Nova Scotian clinical variant are less severely affected.^{[1] [2] [3] [4] [5] [6] [7] [8] [9] [10] [11] [12] [13] [14] [15] [16] [17] [18] [19]}

Function

[NPC1_HUMAN] Intracellular cholesterol transporter which acts in concert with NPC2 and plays an important role in the egress of cholesterol from the endosomal/lysosomal compartment. Both NPC1 and NPC2 function as the cellular 'tag team duo' (TTD) to catalyze the mobilization of cholesterol within the multivesicular environment of the late endosome (LE) to effect egress through the limiting bilayer of the LE. NPC2 binds unesterified cholesterol that has been released from LDLs in the lumen of the late endosomes/lysosomes and transfers it to the cholesterol-binding pocket of the N-terminal domain of NPC1. Cholesterol binds to NPC1 with the hydroxyl group buried in the binding pocket and is exported from the limiting membrane of late endosomes/ lysosomes to the ER and plasma membrane by an unknown mechanism. Binds oxysterol with higher affinity than cholesterol. May play a role in vesicular trafficking in glia, a process that may be crucial for maintaining the structural and functional integrity of nerve terminals.^[20] [VGP_EBOZ5] GP1 is responsible for binding to the receptor(s) on target cells. Interacts with CD209/DC-SIGN and CLEC4M/DC-SIGNR which act as cofactors for virus entry into the host cell. Binding to CD209 and CLEC4M, which are respectively found on dendritic cells (DCs), and on endothelial cells of liver sinusoids and lymph node sinuses, facilitate infection of macrophages and endothelial cells. These interactions not only facilitate virus cell entry, but also allow capture of viral particles by DCs and subsequent transmission to susceptible cells without DCs infection (trans infection). Binding to the macrophage specific lectin CLEC10A also seems to enhance virus infectivity. Interaction with FOLR1/folate receptor alpha may be a cofactor for virus entry in some cell types, although results are contradictory. Members of the Tyro3 receptor tyrosine kinase family also seem to be cell entry factors in filovirus infection. Once attached, the virions are internalized through clathrin-dependent endocytosis and/or macropinocytosis. After internalization of the virus into the endosomes of the host cell, proteolysis of GP1 by two cysteine proteases, CTSB/cathepsin B and CTSL/cathepsin L presumably induces a conformational change of GP2, unmasking its fusion peptide and initiating membranes fusion (By similarity). GP2 acts as a class I viral fusion protein. Under the current model, the protein has at least 3 conformational states: pre-fusion native state, pre-hairpin intermediate state, and post-fusion hairpin state. During viral and target cell membrane fusion, the coiled coil regions (heptad repeats) assume a trimer-of-hairpins structure, positioning the fusion peptide in close proximity to the C-terminal region of the ectodomain. The formation of this structure appears to drive apposition and subsequent fusion of viral and target cell membranes. Responsible for penetration of the virus into the cell cytoplasm by mediating the fusion of the membrane of the endocytosed virus particle with the endosomal membrane. Low pH in endosomes induces an irreversible conformational change in GP2, releasing the fusion hydrophobic peptide (By similarity). GP1,2 mediates endothelial cell activation and decreases endothelial barrier function. Mediates activation of primary macrophages. At terminal stages of the viral infection, when its expression is high, GP1,2 down-modulates the expression of various host cell surface molecules that are essential for immune surveillance and cell adhesion. Down-modulates integrins ITGA1, ITGA2, ITGA3, ITGA4, ITGA5, ITGA6, ITGAV and ITGB1. GP1,2 alters the cellular recycling of the dimer alpha-V/beta-3 via a dynamin-dependent pathway. Decrease in the host cell surface expression of various adhesion molecules may lead to cell detachment, contributing to the disruption of blood vessel integrity and hemorrhages developed during Ebola virus infection (cytotoxicity). This cytotoxicity appears late in the infection, only after the massive release of viral particles by infected cells. Down-modulation of host MHC-I, leading to altered recognition by immune cells, may explain the immune suppression and inflammatory dysfunction linked to Ebola infection. Also down-modulates EGFR surface expression (By similarity). GP2delta is part of the complex GP1,2delta released by host ADAM17 metalloprotease. This secreted complex may play a role in the pathogenesis of the virus by efficiently blocking the neutralizing antibodies that would otherwise neutralize the virus surface glycoproteins GP1,2. Might therefore contribute to the lack of inflammatory reaction seen during infection in spite the of extensive necrosis and massive virus production. GP1,2delta does not seem to be involved in activation of primary macrophages (By similarity).

See Also

• Glycoprotein GP 3D structures

References

1. ↑ Carstea ED, Morris JA, Coleman KG, Loftus SK, Zhang D, Cummings C, Gu J, Rosenfeld MA, Pavan WJ, Krizman DB, Nagle J, Polymeropoulos MH, Sturley SL, Ioannou YA, Higgins ME, Comly M, Cooney A, Brown A, Kaneski CR, Blanchette-Mackie EJ, Dwyer NK, Neufeld EB, Chang TY, Liscum L, Strauss JF 3rd, Ohno K, Zeigler M, Carmi R, Sokol J, Markie D, O'Neill RR, van Diggelen OP, Elleder M, Patterson MC, Brady RO, Vanier MT, Pentchev PG, Tagle DA. Niemann-Pick C1 disease gene: homology to mediators of cholesterol homeostasis. Science. 1997 Jul 11;277(5323):228-31. PMID:9211849
2. ↑ Bauer P, Knoblich R, Bauer C, Finckh U, Hufen A, Kropp J, Braun S, Kustermann-Kuhn B, Schmidt D, Harzer K, Rolfs A. NPC1: Complete genomic sequence, mutation analysis, and characterization of haplotypes. Hum Mutat. 2002 Jan;19(1):30-8. PMID:11754101 doi:10.1002/humu.10016
3. ↑ Greer WL, Riddell DC, Gillan TL, Girouard GS, Sparrow SM, Byers DM, Dobson MJ, Neumann PE. The Nova Scotia (type D) form of Niemann-Pick disease is caused by a G3097-->T transversion in NPC1. Am J Hum Genet. 1998 Jul;63(1):52-4. PMID:9634529 doi:10.1086/301931
4. ↑ Greer WL, Dobson MJ, Girouard GS, Byers DM, Riddell DC, Neumann PE. Mutations in NPC1 highlight a conserved NPC1-specific cysteine-rich domain. Am J Hum Genet. 1999 Nov;65(5):1252-60. PMID:10521290
5. ↑ Millat G, Marcais C, Rafi MA, Yamamoto T, Morris JA, Pentchev PG, Ohno K, Wenger DA, Vanier MT. Niemann-Pick C1 disease: the I1061T substitution is a frequent mutant allele in patients of Western European descent and correlates with a classic juvenile phenotype. Am J Hum Genet. 1999 Nov;65(5):1321-9. PMID:10521297 doi:10.1086/302626
6. ↑ Yamamoto T, Nanba E, Ninomiya H, Higaki K, Taniguchi M, Zhang H, Akaboshi S, Watanabe Y, Takeshima T, Inui K, Okada S, Tanaka A, Sakuragawa N, Millat G, Vanier MT, Morris JA, Pentchev PG, Ohno K. NPC1 gene mutations in Japanese patients with Niemann-Pick disease type C. Hum Genet. 1999 Jul-Aug;105(1-2):10-6. PMID:10480349
7. ↑ Yamamoto T, Ninomiya H, Matsumoto M, Ohta Y, Nanba E, Tsutsumi Y, Yamakawa K, Millat G, Vanier MT, Pentchev PG, Ohno K. Genotype-phenotype relationship of Niemann-Pick disease type C: a possible correlation between clinical onset and levels of NPC1 protein in isolated skin fibroblasts. J Med Genet. 2000 Sep;37(9):707-12. PMID:11182931
8. ↑ Sun X, Marks DL, Park WD, Wheatley CL, Puri V, O'Brien JF, Kraft DL, Lundquist PA, Patterson MC, Pagano RE, Snow K. Niemann-Pick C variant detection by altered sphingolipid trafficking and correlation with mutations within a specific domain of NPC1. Am J Hum Genet. 2001 Jun;68(6):1361-72. Epub 2001 May 9. PMID:11349231 doi:S0002-9297(07)61047-7
9. ↑ Millat G, Marcais C, Tomasetto C, Chikh K, Fensom AH, Harzer K, Wenger DA, Ohno K, Vanier MT. Niemann-Pick C1 disease: correlations between NPC1 mutations, levels of NPC1 protein, and phenotypes emphasize the functional significance of the putative sterol-sensing domain and of the cysteine-rich luminal loop. Am J Hum Genet. 2001 Jun;68(6):1373-85. Epub 2001 May 1. PMID:11333381 doi:10.1086/320606
10. ↑ Meiner V, Shpitzen S, Mandel H, Klar A, Ben-Neriah Z, Zlotogora J, Sagi M, Lossos A, Bargal R, Sury V, Carmi R, Leitersdorf E, Zeigler M. Clinical-biochemical correlation in molecularly characterized patients with Niemann-Pick type C. Genet Med. 2001 Sep-Oct;3(5):343-8. PMID:11545687
11. ↑ Ribeiro I, Marcao A, Amaral O, Sa Miranda MC, Vanier MT, Millat G. Niemann-Pick type C disease: NPC1 mutations associated with severe and mild cellular cholesterol trafficking alterations. Hum Genet. 2001 Jul;109(1):24-32. PMID:11479732
12. ↑ Kaminski WE, Klunemann HH, Ibach B, Aslanidis C, Klein HE, Schmitz G. Identification of novel mutations in the NPC1 gene in German patients with Niemann-Pick C disease. J Inherit Metab Dis. 2002 Sep;25(5):385-9. PMID:12408188
13. ↑ Tarugi P, Ballarini G, Bembi B, Battisti C, Palmeri S, Panzani F, Di Leo E, Martini C, Federico A, Calandra S. Niemann-Pick type C disease: mutations of NPC1 gene and evidence of abnormal expression of some mutant alleles in fibroblasts. J Lipid Res. 2002 Nov;43(11):1908-19. PMID:12401890
14. ↑ Blom TS, Linder MD, Snow K, Pihko H, Hess MW, Jokitalo E, Veckman V, Syvanen AC, Ikonen E. Defective endocytic trafficking of NPC1 and NPC2 underlying infantile Niemann-Pick type C disease. Hum Mol Genet. 2003 Feb 1;12(3):257-72. PMID:12554680
15. ↑ Park WD, O'Brien JF, Lundquist PA, Kraft DL, Vockley CW, Karnes PS, Patterson MC, Snow K. Identification of 58 novel mutations in Niemann-Pick disease type C: correlation with biochemical phenotype and importance of PTC1-like domains in NPC1. Hum Mutat. 2003 Oct;22(4):313-25. PMID:12955717 doi:http://dx.doi.org/10.1002/humu.10255
16. ↑ Fernandez-Valero EM, Ballart A, Iturriaga C, Lluch M, Macias J, Vanier MT, Pineda M, Coll MJ. Identification of 25 new mutations in 40 unrelated Spanish Niemann-Pick type C patients: genotype-phenotype correlations. Clin Genet. 2005 Sep;68(3):245-54. PMID:16098014 doi:CGE490
17. ↑ Yang CC, Su YN, Chiou PC, Fietz MJ, Yu CL, Hwu WL, Lee MJ. Six novel NPC1 mutations in Chinese patients with Niemann-Pick disease type C. J Neurol Neurosurg Psychiatry. 2005 Apr;76(4):592-5. PMID:15774455 doi:10.1136/jnnp.2004.046045
18. ↑ Millat G, Bailo N, Molinero S, Rodriguez C, Chikh K, Vanier MT. 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. Mol Genet Metab. 2005 Sep-Oct;86(1-2):220-32. PMID:16126423 doi:10.1016/j.ymgme.2005.07.007
19. ↑ Dvorakova L, Sikora J, Hrebicek M, Hulkova H, Bouckova M, Stolnaja L, Elleder M. Subclinical course of adult visceral Niemann-Pick type C1 disease. A rare or underdiagnosed disorder? J Inherit Metab Dis. 2006 Aug;29(4):591. Epub 2006 Jun 26. PMID:16802107 doi:10.1007/s10545-006-0330-z
20. ↑ Infante RE, Wang ML, Radhakrishnan A, Kwon HJ, Brown MS, Goldstein JL. NPC2 facilitates bidirectional transfer of cholesterol between NPC1 and lipid bilayers, a step in cholesterol egress from lysosomes. Proc Natl Acad Sci U S A. 2008 Oct 7;105(40):15287-92. doi:, 10.1073/pnas.0807328105. Epub 2008 Sep 4. PMID:18772377 doi:10.1073/pnas.0807328105
21. ↑ Gong X, Qian H, Zhou X, Wu J, Wan T, Cao P, Huang W, Zhao X, Wang X, Wang P, Shi Y, Gao GF, Zhou Q, Yan N. Structural Insights into the Niemann-Pick C1 (NPC1)-Mediated Cholesterol Transfer and Ebola Infection. Cell. 2016 Jun 2;165(6):1467-78. doi: 10.1016/j.cell.2016.05.022. Epub 2016 May, 26. PMID:27238017 doi:http://dx.doi.org/10.1016/j.cell.2016.05.022