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3.A.20.1.1
The peroxisomal importing translocon with receptors: Pex5p and Pex7p; and receptor facilitator: Pex4p. Peroxisomal biogenesis factor PEX26 is a membrane anchor for the multi-subunit PEX1-PEX6 protein complex that controls ubiquitination and dislocation of PEX5 cargo receptors for peroxisomal matrix protein import. PEX26 associates with the peroxisomal translocation pore via PEX14 (Guder et al. 2018). Luminal peroxisomal proteins are imported from the cytosol by mobile receptors, which then recycle back to the cytosol by a poorly understood process (Feng et al. 2022). Recycling requires receptor modification by a membrane-embedded ubiquitin ligase complex comprising three RING finger domain-containing proteins (Pex2, Pex10 and Pex12). Feng et al. 2022 reported a cryo-EM structure of the ligase complex, which together with biochemical and in vivo experiments reveals its function as a retrotranslocation channel for peroxisomal import receptors. Each subunit of the complex contributes five transmembrane segments that co-assemble into an open channel. The three ring finger domains form a cytosolic tower, with ring finger 2 (RF2) positioned above the channel pore. The N terminus of a recycling receptor is inserted from the peroxisomal lumen into the pore and monoubiquitylated by RF2 to enable extraction into the cytosol. If recycling is compromised, receptors are polyubiquitylated by the concerted action of RF10 and RF12 and degraded. This polyubiquitylation pathway also maintains the homeostasis of other peroxisomal import factors. Thus, a crucial step during peroxisomal protein import is clarified, and it explains why mutations in the ligase complex cause human disease (Feng et al. 2022).

Accession Number:Q7Z412
Protein Name:Peroxisome assembly protein 26
Length:305
Molecular Weight:33898.00
Species:Homo sapiens (Human) [9606]
Location1 / Topology2 / Orientation3: Peroxisome membrane1 / Single-pass type II membrane protein2
Substrate protein polypeptide chain

Cross database links:

RefSeq: NP_001121121.1    NP_060399.1   
Entrez Gene ID: 55670   
Pfam: PF07163   
OMIM: 202370  phenotype
214100  phenotype
266510  phenotype
601539  phenotype
608666  gene+phenotype
KEGG: hsa:55670   

Gene Ontology

GO:0005779 C:integral to peroxisomal membrane
GO:0008022 F:protein C-terminus binding
GO:0032403 F:protein complex binding
GO:0016558 P:protein import into peroxisome matrix
GO:0045046 P:protein import into peroxisome membrane

References (7)

[1] “The pathogenic peroxin Pex26p recruits the Pex1p-Pex6p AAA ATPase complexes to peroxisomes.”  Matsumoto N.et.al.   12717447
[2] “Mutations in novel peroxin gene PEX26 that cause peroxisome-biogenesis disorders of complementation group 8 provide a genotype-phenotype correlation.”  Matsumoto N.et.al.   12851857
[3] “Complete sequencing and characterization of 21,243 full-length human cDNAs.”  Ota T.et.al.   14702039
[4] “A genome annotation-driven approach to cloning the human ORFeome.”  Collins J.E.et.al.   15461802
[5] “The DNA sequence of human chromosome 22.”  Dunham I.et.al.   10591208
[6] “The status, quality, and expansion of the NIH full-length cDNA project: the Mammalian Gene Collection (MGC).”  The MGC Project Teamet.al.   15489334
[7] “Identification of novel mutations and sequence variation in the Zellweger syndrome spectrum of peroxisome biogenesis disorders.”  Yik W.Y.et.al.   19105186

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FASTA formatted sequence
1:	MKSDSSTSAA PLRGLGGPLR SSEPVRAVPA RAPAVDLLEE AADLLVVHLD FRAALETCER 
61:	AWQSLANHAV AEEPAGTSLE VKCSLCVVGI QALAEMDRWQ EVLSWVLQYY QVPEKLPPKV 
121:	LELCILLYSK MQEPGAVLDV VGAWLQDPAN QNLPEYGALA EFHVQRVLLP LGCLSEAEEL 
181:	VVGSAAFGEE RRLDVLQAIH TARQQQKQEH SGSEEAQKPN LEGSVSHKFL SLPMLVRQLW 
241:	DSAVSHFFSL PFKKSLLAAL ILCLLVVRFD PASPSSLHFL YKLAQLFRWI RKAAFSRLYQ 
301:	LRIRD