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. 2016 Oct 31;113(46):E7307–E7316. doi: 10.1073/pnas.1613530113

Fig. 7.

Fig. 7.

A working model for SP1’s role in peroxisome protein import in Arabidopsis. PEX5 and PEX7 are cytosolic receptors for peroxisome matrix proteins. The cargo-receptor complexes dock to the docking site formed by two membrane proteins, PEX13 and PEX14. The exact function of the E3 ubiquitin ligases PEX2, PEX10, and PEX12 in Arabidopsis is still unclear. The export of PEX5 to the cytosol is dependent on the ubiquitin-conjugating enzyme PEX4, which needs PEX22 as its membrane anchor, and the AAA ATPases PEX6 and PEX1, which are tethered to the membrane by APEM9. The balance between cargo translocation and receptor recycling is also important for the function of the machinery. SP1 interacts with PEX13, PEX14, and PEX2 in co-IP. SP1 promotes the ubiquitination and destabilization of PEX13 and promotes the destabilization of PEX14, PEX2, PEX10, and PEX12, at least in tobacco. Therefore, SP1 regulates peroxisome biogenesis by associating with and destabilizing PEX13 and possibly several other peroxins in peroxisome matrix protein import. Double-ended arrows indicate a physical interaction in co-IP. Dashed arrows indicate hypothesized SP1-mediated ubiquitination. PEX13 is shown in bold because it is the most likely target of SP1.