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1.I.1.1.3
Nuclear Pore Complex, NPC, with 86 protein components.  NPCs mediate nucleocytoplasmic transport and gain transport selectivity through nucleoporin FG domains. Chug et al. 2015 reported a structural analysis of the frog FG Nup62•58•54 complex. It comprises a ≈13 nanometer-long trimerization interface with an unusual 2W3F coil, a canonical heterotrimeric coiled coil, and a kink that enforces a compact six-helix bundle. Nup54 also contains a ferredoxin-like domain. Chug et al. 2015 further identified a heterotrimeric Nup93-binding module for NPC anchorage. The quaternary structure alternations in the Nup62 complex, which were previously proposed to trigger a general gating of the NPC, are incompatible with the trimer structure. Chug et al. 2015 suggested that the highly elongated Nup62 complex projects barrier-forming FG repeats far into the central NPC channel, supporting a barrier that guards the entire cross section. The Sun1/UNC84A protein and Sun2/UNC84B may function redundantly in early HIV-1 infection steps and therefore influence HIV-1 replication and pathogenesis (Schaller et al. 2017).  The integral transmembrane nucleoporin Pom121 functionally links nuclear pore complex assembly to nuclear envelope formation (Antonin et al. 2005) and ensures efficient HIV-1 pre-integration complex nuclear import (Guo et al. 2018). Mechanosensing at the nuclear envelope by nuclear pore complex stretch activation involves cell membrane integrins (TC# 8.A.54) and SUN proteins, SUN1 and SUN2, in the nuclear membrane (Donnaloja et al. 2019). TMX2 is a thioredoxin-like protein that facilitates the transport of proteins across the nuclear membrane (Oguro and Imaoka 2019). Torsin ATPase deficiency leads to defects in nuclear pore biogenesis and sequestration of the myelokd leukemia factor 2, MLF2 (Rampello et al. 2020).    G4C2 repeat RNA initiates a POM121-mediated reduction in specific nucleoporins (Coyne et al. 2020) (Pom121: acc# A8CG34). Defects in nucleocytoplasmic transport and accumulation of specific nuclear-pore-complex-associated proteins play roles in multiple neurodegenerative diseases, including C9orf72 Amyotrophic Lateral Sclerosis and Frontotemporal Dementia (ALS/FTD). Using super-resolution structured illumination microscopy, Coyne et al. 2020 have explored the mechanism by which nucleoporins are altered in nuclei isolated from C9orf72 induced pluripotent stem-cell-derived neurons (iPSNs). Of the 23 nucleoporins evaluated, they observed a reduction in a subset of 8, including key components of the nuclear pore complex scaffold and the transmembrane nucleoporin POM121. Reduction in POM121 appeared to initiate a decrease in the expression of seven additional nucleoporins, ultimately affecting the localization of the Ran GTPase and subsequent cellular toxicity in C9orf72 iPSNs. Thus, the expression of expanded C9orf72 ALS/FTD repeat RNA affects nuclear POM121 expression in the initiation of a pathological cascade affecting nucleoporin levels within neuronal nuclei and ultimately downstream neuronal survival (Coyne et al. 2020).  

Accession Number:O00505
Protein Name:Importin subunit alpha-4
Length:521
Molecular Weight:57811.00
Species:Homo sapiens (Human) [9606]
Number of TMSs:2
Location1 / Topology2 / Orientation3: Cytoplasm1
Substrate proteins, RNA

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FASTA formatted sequence
1:	MAENPSLENH RIKSFKNKGR DVETMRRHRN EVTVELRKNK RDEHLLKKRN VPQEESLEDS 
61:	DVDADFKAQN VTLEAILQNA TSDNPVVQLS AVQAARKLLS SDRNPPIDDL IKSGILPILV 
121:	KCLERDDNPS LQFEAAWALT NIASGTSAQT QAVVQSNAVP LFLRLLRSPH QNVCEQAVWA 
181:	LGNIIGDGPQ CRDYVISLGV VKPLLSFISP SIPITFLRNV TWVIVNLCRN KDPPPPMETV 
241:	QEILPALCVL IYHTDINILV DTVWALSYLT DGGNEQIQMV IDSGVVPFLV PLLSHQEVKV 
301:	QTAALRAVGN IVTGTDEQTQ VVLNCDVLSH FPNLLSHPKE KINKEAVWFL SNITAGNQQQ 
361:	VQAVIDAGLI PMIIHQLAKG DFGTQKEAAW AISNLTISGR KDQVEYLVQQ NVIPPFCNLL 
421:	SVKDSQVVQV VLDGLKNILI MAGDEASTIA EIIEECGGLE KIEVLQQHEN EDIYKLAFEI 
481:	IDQYFSGDDI DEDPCLIPEA TQGGTYNFDP TANLQTKEFN F