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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).

Metazoa, Chordata
The peroxisomal translocon of Homo sapiens
Pex1p (Peroxisomal AAA-type ATPase) (O43933)
Pex2p (Peroxisome assembly factor 1, PAF1; RING finger protein) (P28328)
Pex4p (183 aas; 0-1 TMS) (P29340) (Saccharomyces cerevisiae)
Pex5p (639 aas; 0-1 TMS) (O09012) (mouse)
Pex6p (Peroxisomal AAA-type ATPase) (Q13608)
Pex7p (323 aas; 0-2 TMSs) (O00628)
Pex10p (326 aas; 3-5 TMSs) (O60683)
Pex12p (359 aas; 2-4 TMSs) (O00623)
Pex13p (403 aas; 1-2 TMSs) (Q92968)
Pex14p (377 aas; 0-1 TMS) (O75381)
Pex26 (305 aas; 5-6 TMSs) (Q7Z412)
Uba1 (Ubc9; UbcE9; Ube21) (158aas; 0 TMSs) (P63279)
Ubc4 (UbD2/E2) (147aas; 0 TMSs) (P62837) 

The peroxin complex for the import of proteins into the matrix of peroxisomes (Prestele et al., 2010). Note: PexII has five paralogues, PexIIA-E.

Viridiplantae, Streptophyta
Peroxin (PEX) complex of Arabidopsis thaliana
Pex1 (Q9LJ64)
Pex2 (Q9XIB6)
Pex3 (Q9XIL9)
Pex4 (O81765)
Pex5 (Q9FMA3)
Pex6 (Q8RY16)
Pex7 (Q9LP54)
Pex10 (Q9SYU4)
Pex11A (Q9FZF1)
Pex12 (Q9M841)
Pex13 (Q9SRR0)
Pex14 (Q9FE40)

Glycosomal membrane protein insertion apparatus.  Two proteins included in the system are PEX14 and PEX19 which target to the peroxisome in several other organisms, but in T. brucei, they target to the glycosome.  By contrast, PEX10 and PEX12 are involved in targetting to the peroxisome (Saveria et al. 2007). Altogether, PEX1, 2, 5, 6, 10, 11, 12, 14, 16, and 19 have been identified in T. brucei and are listed here. Inhibitors of PEX14 block protein import into glycosomes and kill Trypanosma parasites (Dawidowski et al. 2017). The glycosomal membrane-associated Leishmania donovani protein PEX14, which plays a crucial role in protein import from the cytosol to the glycosomal matrix, consists of three domains: an N-terminal domain where the signalling molecule binds, a transmembrane domain and an 84-residue coiled-coil domain (CC) that is responsible for oligomerization. CCs are versatile domains that participate in a variety of functions including supramolecular assembly, cellular signalling and transport (Shakya and Pratap 2020). Bioinformatic analyses indicate that the N-terminal region of TbPEX11 contains an amphiphilic helix and several putative TOM20 recognition motifs. Thus, the extreme N-terminal region of TbPEX11 contains a cryptic N-terminal signal that directs PEX11 to the mitochondrion if its glycosomal transport is blocked (Krishna et al. 2023).

Peroxisome/glycosome protein insertion apparatus of Trypanosoma brucei brucei
Pex1, 911 aas
Pex2, 332 aas
Pex5, 655 aas
Pex6, 982 aas
Pex10, 298 aas
Pex11, 218 aas
Pex12, 395 aas
Pex14, 366 aas
Pex16, 453 aas
Pex19, 285 aas

The peroxysomal protein import translocon

Peroxysomal protein import translocon of Leishmania major
Glycosome import protein (Q4Q9L4)
Peroxisomal targeting signal-2 receptor (Q4VQ66)
Putative peroxin 13 (Q4QDL4)
Putative peroxin 14 (Q4QBZ9)
Putative peroxisome assembly protein (Q4QD90)
RING finger protein (Q95ZB8)
Putative glycosomal membrane protein (Q4Q838)

The peroxisome complex for protein import into peroxisomes (Kiel et al. 2006).

Fungi, Ascomycota
Peroxin complex of Saccharomyces cerevisiae
PEX1 (P24004)
PEX2 (P32800)
PEX3 (P28795)
PEX4 (P29340)
PEX5 (P35056)
PEX6 (P33760)
PEX7 (P39108)
PEX8 (P53248)
PEX10 (Q05568)
PEX11 (Q12462)
PEX12 (Q04370)
PEX13 (P80667)
PEX14 (P53112)
PEX15 (Q08215)
PEX17 (P40155)
PEX18 (P38855)
PEX19 (Q07418)
PEX21 (P50091)
PEX22 (P39718)
PEX23 (Q06169)
PEX23-like (P40031)
PEX24 (P38848)
PEX25 (Q02969)
PEX27 (Q08580)
PEX28 (P38848)
PEX29 (Q03370)
PEX30 (Q06169)
PEX31 (P53203)
PEX32 (P38292)
PEX34 (P25584)