UBE3A
Ubikvitin-protein ligaza E3A (UBE3A), znana i kao E6AP ubikvitin-protein ligaza (E6AP) je enzim koji je kod ljudi kodiran genom UBE3A. Ovaj enzim je uključen u ciljanje proteina za razgradnju unutar ćelije.
Razgradnja proteina je normalan proces koji uklanja oštećene ili nepotrebne proteine i pomaže u održavanju normalnih funkcija ćelija. Ubikvitin proteinska ligaza E3A veže mali marker protein nazvan ubikvitin na proteine koji bi trebali biti razgrađeni. Ćelijske strukture zvane proteasomi prepoznaju i probavljaju proteine označene ubikvitinom.
Obje kopije gena UBE3A aktivne su u većini tjelesnih tkiva. U većini neurona, međutim, normalno je aktivna samo kopija naslijeđena od majke date osobe (majčina kopija); ovo je poznato kao očinsko utiskivanje. Noviji dokazi pokazuju da bar neke glijne ćelije i neuroni mogu ispoljavati bialelnu ekspresiju UBE3A.[5][6] Zato je potreban dalji rad na ocrtavanju kompletne mape utiskivanja UBE3A kod ljudi i modelnih organizama, kao što su miševi.
Smatra se da se utišavanje Ube3a na očinskom alelu događa putem Ube3a-ATS dijela lincRNK zvan LNCAT (engleski: Large Non-Coding Antisense Transcript).[7]
Gen UBE3A nalazi se na dugom (q) kraku hromosoma 15, između položaja 11 i 13, od baznog para 23,133.488 do baznog para 23,235.220.
Aminokiselinska sekvenca
[uredi | uredi izvor]Dužina polipeptidnog lanca je 875 aminokiselina, a molekulska težina 100.688 Da.[8]
10 | 20 | 30 | 40 | 50 | ||||
---|---|---|---|---|---|---|---|---|
MEKLHQCYWK | SGEPQSDDIE | ASRMKRAAAK | HLIERYYHQL | TEGCGNEACT | ||||
NEFCASCPTF | LRMDNNAAAI | KALELYKINA | KLCDPHPSKK | GASSAYLENS | ||||
KGAPNNSCSE | IKMNKKGARI | DFKDVTYLTE | EKVYEILELC | REREDYSPLI | ||||
RVIGRVFSSA | EALVQSFRKV | KQHTKEELKS | LQAKDEDKDE | DEKEKAACSA | ||||
AAMEEDSEAS | SSRIGDSSQG | DNNLQKLGPD | DVSVDIDAIR | RVYTRLLSNE | ||||
KIETAFLNAL | VYLSPNVECD | LTYHNVYSRD | PNYLNLFIIV | MENRNLHSPE | ||||
YLEMALPLFC | KAMSKLPLAA | QGKLIRLWSK | YNADQIRRMM | ETFQQLITYK | ||||
VISNEFNSRN | LVNDDDAIVA | ASKCLKMVYY | ANVVGGEVDT | NHNEEDDEEP | ||||
IPESSELTLQ | ELLGEERRNK | KGPRVDPLET | ELGVKTLDCR | KPLIPFEEFI | ||||
NEPLNEVLEM | DKDYTFFKVE | TENKFSFMTC | PFILNAVTKN | LGLYYDNRIR | ||||
MYSERRITVL | YSLVQGQQLN | PYLRLKVRRD | HIIDDALVRL | EMIAMENPAD | ||||
LKKQLYVEFE | GEQGVDEGGV | SKEFFQLVVE | EIFNPDIGMF | TYDESTKLFW | ||||
FNPSSFETEG | QFTLIGIVLG | LAIYNNCILD | VHFPMVVYRK | LMGKKGTFRD | ||||
LGDSHPVLYQ | SLKDLLEYEG | NVEDDMMITF | QISQTDLFGN | PMMYDLKENG | ||||
DKIPITNENR | KEFVNLYSDY | ILNKSVEKQF | KAFRRGFHMV | TNESPLKYLF | ||||
RPEEIELLIC | GSRNLDFQAL | EETTEYDGGY | TRDSVLIREF | WEIVHSFTDE | ||||
QKRLFLQFTT | GTDRAPVGGL | GKLKMIIAKN | GPDTERLPTS | HTCFNVLLLP | ||||
EYSSKEKLKE | RLLKAITYAK | GFGML |
- Simboli
C: Cistein
D: Asparaginska kiselina
E: Glutaminska kiselina
F: Fenilalanin
G: Glicin
H: Histidin
I: Izoleucin
K: Lizin
L: Leucin
M: Metionin
N: Asparagin
P: Prolin
Q: Glutamin
R: Arginin
S: Serin
T: Treonin
V: Valin
W: Triptofan
Y: Tirozin
Klinički značaj
[uredi | uredi izvor]Mutacije unutar gena UBE3A odgovorne su za neke slučajeve Angelmanovog i Prader-Willijevog sindroma. Većina ovih mutacija rezultira abnormalno kratkom, nefunkcionalnom verzijom ubikvitin proteinske ligaze E3A. Budući da je kopija gena naslijeđena od oca osobe (očinska kopija) obično je neaktivna u mozgu, a mutacija u preostaloj majčinskoj kopiji sprečava stvaranje bilo kojeg enzima u mozgu. Ovaj gubitak funkcije enzima vjerovatno uzrokuje karakteristična obilježja ova dva stanja.
Gen UBE3A bnalazi se unutar ljudskog hromosomskog područja 15q11-13. Ostale abnormalnosti u ovoj regiji hromosoma 15 također mogu izazvati Angelmanov sindrom. Te hromosomske promjene uključuju delecije, preuređivanje (translokacije) genetičkog materijala i druge abnormalnosti. Poput mutacija unutar gena, ove hromosomske promjene sprečavaju stvaranje bilo koje funkcionalne ubikvitin-proteinske ligaze E3A u mozgu.
Interakcije
[uredi | uredi izvor]Pokazano je da UBE3A komjunicira sa:
Reference
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- ^ "Mouse PubMed Reference:". National Center for Biotechnology Information, U.S. National Library of Medicine.
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Dopunska literatura
[uredi | uredi izvor]- Bittel DC, Kibiryeva N, Talebizadeh Z, Driscoll DJ, Butler MG (januar 2005). "Microarray analysis of gene/transcript expression in Angelman syndrome: deletion versus UPD". Genomics. 85 (1): 85–91. doi:10.1016/j.ygeno.2004.10.010. PMC 6800218. PMID 15607424.
- Cassidy SB, Dykens E, Williams CA (2000). "Prader-Willi and Angelman syndromes: sister imprinted disorders". American Journal of Medical Genetics. 97 (2): 136–46. doi:10.1002/1096-8628(200022)97:2<136::AID-AJMG5>3.0.CO;2-V. PMID 11180221.
- Clayton-Smith J, Laan L (februar 2003). "Angelman syndrome: a review of the clinical and genetic aspects". Journal of Medical Genetics. 40 (2): 87–95. doi:10.1136/jmg.40.2.87. PMC 1735357. PMID 12566516.
- Fang P, Lev-Lehman E, Tsai TF, Matsuura T, Benton CS, Sutcliffe JS, Christian SL, Kubota T, Halley DJ, Meijers-Heijboer H, Langlois S, Graham JM, Beuten J, Willems PJ, Ledbetter DH, Beaudet AL (januar 1999). "The spectrum of mutations in UBE3A causing Angelman syndrome" (PDF). Human Molecular Genetics. 8 (1): 129–35. doi:10.1093/hmg/8.1.129. PMID 9887341.
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