Komplementni faktor I, znan i kao inaktivator C3b/C4b, jest protein /enzim koji je kod ljudi kodiran genom CFI sa hromosoma 4. To je protein komplementnog sistema, prvi put izoliran 1966. iz zamorčevog seruma,[5] koji regulira aktivaciju komplementa cijepanjem ćelijske ili fluidne faze C3b i C4b.[6] To je rastvorljivi glikoprotein koji cirkulira ljudskom krvlju, u prosječnoj koncentraciji od 35μg/mL.[7]
Kratke činjenice Dostupne strukture, PDB ...
Zatvori
Dužina polipeptidnog lanca je 583 aminokiselina, а molekulska težina 65.750 Da.[8]
10 | | 20 | | 30 | | 40 | | 50 |
MKLLHVFLLF | | LCFHLRFCKV | | TYTSQEDLVE | | KKCLAKKYTH | | LSCDKVFCQP |
WQRCIEGTCV | | CKLPYQCPKN | | GTAVCATNRR | | SFPTYCQQKS | | LECLHPGTKF |
LNNGTCTAEG | | KFSVSLKHGN | | TDSEGIVEVK | | LVDQDKTMFI | | CKSSWSMREA |
NVACLDLGFQ | | QGADTQRRFK | | LSDLSINSTE | | CLHVHCRGLE | | TSLAECTFTK |
RRTMGYQDFA | | DVVCYTQKAD | | SPMDDFFQCV | | NGKYISQMKA | | CDGINDCGDQ |
SDELCCKACQ | | GKGFHCKSGV | | CIPSQYQCNG | | EVDCITGEDE | | VGCAGFASVT |
QEETEILTAD | | MDAERRRIKS | | LLPKLSCGVK | | NRMHIRRKRI | | VGGKRAQLGD |
LPWQVAIKDA | | SGITCGGIYI | | GGCWILTAAH | | CLRASKTHRY | | QIWTTVVDWI |
HPDLKRIVIE | | YVDRIIFHEN | | YNAGTYQNDI | | ALIEMKKDGN | | KKDCELPRSI |
PACVPWSPYL | | FQPNDTCIVS | | GWGREKDNER | | VFSLQWGEVK | | LISNCSKFYG |
NRFYEKEMEC | | AGTYDGSIDA | | CKGDSGGPLV | | CMDANNVTYV | | WGVVSWGENC |
GKPEFPGVYT | | KVANYFDWIS | | YHVGRPFISQ | | YNV |
Gen za faktor I kod ljudi se nalazi na hromosomu 4.[9] Faktor I sintetizira se najviše u jetri, ali iu monocitima, fibroblastima, keratinocitima i endotelnim ćelijama.[10][11][12] Kada se sintetizira, to je polipeptidni lanac od 66 kDa sa N-vezanim glikanima na šest pozicija.[13] Zatim, faktor I cijepa se pomoću furina, kako bi se dobio zreli protein faktora I, koji je disulfidno povezani dimer teškog (ostaci 19-335, 51 kD) i lahkog lanca (ostaci 340-583, 37 kD).[14] Aktivan je samo zreli protein.
Faktor I je glikoproteinski heterodimer koji se sastoji od disulfidno vezanog teškog i lahkog lanca.[15]
Teški lanac faktora I ima četiri domena: domen FI membranskog napadajućeg kompleksa (FIMAC), CD5 i domen receptora lipoproteina niske gustine 1 i 2 (LDLr1 i LDLr2).[16] Ima inhibitornu ulogu u održavanju enzima neaktivnim sve dok se ne susretne sa kompleksom koji formiraju supstrat (ili C3b ili C4b) i kofaktor proteina (faktor H, C4b-vezujući protein, receptor komplementa 1 i proteinski kofaktor membrane).[17] Nakon vezivanja enzima za kompleks supstrat–kofaktor, interfejs teški–lahki lanac je prekinut, a enzim se aktivira alosterijom.[17] Domeni LDL-receptora sadrže po jedno mjesto vezanja kalcija.
Lahki lanac faktora I sadrži samo domen serin-proteaza. Ovaj domen sadrži katalitskku trijadu His-362, Asp-411 i Ser-507, koja je odgovorna za specifično cijepanje C3b i C4b.[16] Uobičajeni inhibitori proteaze ne inaktiviraju potpuno faktor I[18] ali to mogu učiniti ako je enzim prethodno inkubiran sa svojim supstratom: ovo podržava predloženo preuređenje molekula nakon vezivanja za supstrat.
I teški i lahki lanci nose Asn-vezane glikana, na tri različita glikozilacijska mjesta.
Kristalna struktura ljudskog faktora I je deponovana kaao PDB: 2XRC .
Disregulirana aktivnost faktora I ima kliničke implikacije. Gubitak funkcijskih mutacija u genu za faktor I komplementa dovodi do niskog nivoa faktora I što rezultira povećanom aktivnošću komplementa. Nedostatak faktora I zauzvrat dovodi do niskih nivoa komponente komplementa 3 (C3), faktora B, faktora H i properdina u krvi, zbog neregulirane aktivacije C3-konvertaza i niskog nivoa IgG, zbog gubitka proizvodnje iC3b i C3dg. Pored sljedećih bolesti, nizak faktor I je povezan s rekurentnim bakterijskim infekcijama kod djece.
- Starosno vezana degeneracija makule
Rezultati istraživanja sugeriraju da mutacije u genu CFI doprinose razvoju degeneracije makule povezane sa starenjem.[19] Smatra se da je ovaj doprinos posljedica disregulacije alternativnog puta, što dovodi do povećane upale u očima.[20]
- Sindrom netipske hemolitske uremije
Sindrom netipske hemolitske uremije izazvan je prekomjernom aktivacijom komplementa.[21] Oko 5-10% slučajeva sindroma čini heterozigotost mutacija u domenu gena serin-proteaze CFI.[21]
Nelson RA, Jensen J, Gigli I, Tamura N (mart 1966). "Methods for the separation, purification and measurement of nine components of hemolytic complement in guinea-pig serum". Immunochemistry. 3 (2): 111–35. doi:10.1016/0019-2791(66)90292-8. PMID 5960883. Lachmann PJ, Müller-Eberhard HJ (april 1968). "The demonstration in human serum of "conglutinogen-activating factor" and its effect on the third component of complement". Journal of Immunology. 100 (4): 691–8. PMID 5645214. Julen N, Dauchel H, Lemercier C, Sim RB, Fontaine M, Ripoche J (januar 1992). "In vitro biosynthesis of complement factor I by human endothelial cells". European Journal of Immunology. 22 (1): 213–7. doi:10.1002/eji.1830220131. PMID 1530917. S2CID 30130789. Tsiftsoglou SA, Arnold JN, Roversi P, Crispin MD, Radcliffe C, Lea SM, Dwek RA, Rudd PM, Sim RB (novembar 2006). "Human complement factor I glycosylation: structural and functional characterisation of the N-linked oligosaccharides". Biochimica et Biophysica Acta (BBA) - Proteins and Proteomics. 1764 (11): 1757–66. CiteSeerX 10.1.1.712.1764. doi:10.1016/j.bbapap.2006.09.007. PMID 17055788. Ekdahl KN, Nilsson UR, Nilsson B (juni 1990). "Inhibition of factor I by diisopropylfluorophosphate. Evidence of conformational changes in factor I induced by C3b and additional studies on the specificity of factor I". Journal of Immunology. 144 (11): 4269–74. PMID 2140392.
- Bradley DT, Zipfel PF, Hughes AE (juni 2011). "Complement in age-related macular degeneration: a focus on function". Eye. 25 (6): 683–93. doi:10.1038/eye.2011.37. PMC 3178140. PMID 21394116.
- Chan MR, Thomas CP, Torrealba JR, Djamali A, Fernandez LA, Nishimura CJ, Smith RJ, Samaniego MD (februar 2009). "Recurrent atypical hemolytic uremic syndrome associated with factor I mutation in a living related renal transplant recipient". American Journal of Kidney Diseases. 53 (2): 321–6. doi:10.1053/j.ajkd.2008.06.027. PMC 2879708. PMID 18805611.
- Kalsi G, Kuo PH, Aliev F, Alexander J, McMichael O, Patterson DG, Walsh D, Zhao Z, Schuckit M, Nurnberger J, Edenberg H, Kramer J, Hesselbrock V, Tischfield JA, Vladimirov V, Prescott CA, Dick DM, Kendler KS, Riley BP (juni 2010). "A systematic gene-based screen of chr4q22-q32 identifies association of a novel susceptibility gene, DKK2, with the quantitative trait of alcohol dependence symptom counts". Human Molecular Genetics. 19 (12): 2497–506. doi:10.1093/hmg/ddq112. PMC 2876884. PMID 20332099.
- Nilsson SC, Kalchishkova N, Trouw LA, Fremeaux-Bacchi V, Villoutreix BO, Blom AM (januar 2010). "Mutations in complement factor I as found in atypical hemolytic uremic syndrome lead to either altered secretion or altered function of factor I". European Journal of Immunology. 40 (1): 172–85. doi:10.1002/eji.200939280. PMID 19877009.
- Rose JE, Behm FM, Drgon T, Johnson C, Uhl GR (2010). "Personalized smoking cessation: interactions between nicotine dose, dependence and quit-success genotype score". Molecular Medicine. 16 (7–8): 247–53. doi:10.2119/molmed.2009.00159. PMC 2896464. PMID 20379614.
- Sullivan M, Erlic Z, Hoffmann MM, Arbeiter K, Patzer L, Budde K, Hoppe B, Zeier M, Lhotta K, Rybicki LA, Bock A, Berisha G, Neumann HP (januar 2010). "Epidemiological approach to identifying genetic predispositions for atypical hemolytic uremic syndrome" (PDF). Annals of Human Genetics. 74 (1): 17–26. doi:10.1111/j.1469-1809.2009.00554.x. PMID 20059470. S2CID 24304765.
- Westra D, Volokhina E, van der Heijden E, Vos A, Huigen M, Jansen J, van Kaauwen E, van der Velden T, van de Kar N, van den Heuvel L (juli 2010). "Genetic disorders in complement (regulating) genes in patients with atypical haemolytic uraemic syndrome (aHUS)". Nephrology, Dialysis, Transplantation. 25 (7): 2195–202. doi:10.1093/ndt/gfq010. PMID 20106822.
- Bienaime F, Dragon-Durey MA, Regnier CH, Nilsson SC, Kwan WH, Blouin J, Jablonski M, Renault N, Rameix-Welti MA, Loirat C, Sautés-Fridman C, Villoutreix BO, Blom AM, Fremeaux-Bacchi V (februar 2010). "Mutations in components of complement influence the outcome of Factor I-associated atypical hemolytic uremic syndrome". Kidney International. 77 (4): 339–49. doi:10.1038/ki.2009.472. PMID 20016463.
- Kondo N, Bessho H, Honda S, Negi A (juni 2010). "Additional evidence to support the role of a common variant near the complement factor I gene in susceptibility to age-related macular degeneration". European Journal of Human Genetics. 18 (6): 634–5. doi:10.1038/ejhg.2009.243. PMC 2987347. PMID 20087399.
- Maga TK, Nishimura CJ, Weaver AE, Frees KL, Smith RJ (juni 2010). "Mutations in alternative pathway complement proteins in American patients with atypical hemolytic uremic syndrome". Human Mutation. 31 (6): E1445–60. doi:10.1002/humu.21256. PMID 20513133. S2CID 205919773.
- Reynolds R, Hartnett ME, Atkinson JP, Giclas PC, Rosner B, Seddon JM (decembar 2009). "Plasma complement components and activation fragments: associations with age-related macular degeneration genotypes and phenotypes". Investigative Ophthalmology & Visual Science. 50 (12): 5818–27. doi:10.1167/iovs.09-3928. PMC 2826794. PMID 19661236.
- Shin DH, Webb BM, Nakao M, Smith SL (juli 2009). "Characterization of shark complement factor I gene(s): genomic analysis of a novel shark-specific sequence". Molecular Immunology. 46 (11–12): 2299–308. doi:10.1016/j.molimm.2009.04.002. PMC 2699631. PMID 19423168.
- Nilsson SC, Trouw LA, Renault N, Miteva MA, Genel F, Zelazko M, Marquart H, Muller K, Sjöholm AG, Truedsson L, Villoutreix BO, Blom AM (januar 2009). "Genetic, molecular and functional analyses of complement factor I deficiency". European Journal of Immunology. 39 (1): 310–23. doi:10.1002/eji.200838702. PMID 19065647. S2CID 8445601.
- Fagerness JA, Maller JB, Neale BM, Reynolds RC, Daly MJ, Seddon JM (januar 2009). "Variation near complement factor I is associated with risk of advanced AMD". European Journal of Human Genetics. 17 (1): 100–4. doi:10.1038/ejhg.2008.140. PMC 2985963. PMID 18685559.
- Yuasa I, Irizawa Y, Nishimukai H, Fukumori Y, Umetsu K, Nakayashiki N, Saitou N, Henke L, Henke J (januar 2011). "A hypervariable STR polymorphism in the complement factor I (CFI) gene: Asian-specific alleles". International Journal of Legal Medicine. 125 (1): 121–5. doi:10.1007/s00414-009-0369-0. PMID 19693526. S2CID 37565572.
- Moore I, Strain L, Pappworth I, Kavanagh D, Barlow PN, Herbert AP, Schmidt CQ, Staniforth SJ, Holmes LV, Ward R, Morgan L, Goodship TH, Marchbank KJ (januar 2010). "Association of factor H autoantibodies with deletions of CFHR1, CFHR3, CFHR4, and with mutations in CFH, CFI, CD46, and C3 in patients with atypical hemolytic uremic syndrome". Blood. 115 (2): 379–87. doi:10.1182/blood-2009-05-221549. PMC 2829859. PMID 19861685.
- Li MZ, Yu DM, Yu P, Liu DM, Wang K, Tang XZ (april 2008). "Mitochondrial gene mutations and type 2 diabetes in Chinese families". Chinese Medical Journal. 121 (8): 682–6. doi:10.1097/00029330-200804020-00004. PMID 18701018.
- Nilsson SC, Nita I, Månsson L, Groeneveld TW, Trouw LA, Villoutreix BO, Blom AM (februar 2010). "Analysis of binding sites on complement factor I that are required for its activity". The Journal of Biological Chemistry. 285 (9): 6235–45. doi:10.1074/jbc.M109.097212. PMC 2825419. PMID 20044478.