Peroxisomal Pex11 is a pore-forming protein homologous to TRPM channels

Abstract

More than 30 proteins (Pex proteins) are known to participate in the biogenesis of peroxisomes-ubiquitous oxidative organelles involved in lipid and ROS metabolism. The Pex11 family of homologous proteins is responsible for division and proliferation of peroxisomes. We show that yeast Pex11 is a pore-forming protein sharing sequence similarity with TRPM cation-selective channels. The Pex11 channel with a conductance of Λ=4.1 nS in 1.0M KCl is moderately cation-selective (PK(+)/PCl(-)=1.85) and resistant to voltage-dependent closing. The estimated size of the channel's pore (r~0.6 nm) supports the notion that Pex11 conducts solutes with molecular mass below 300-400 Da. We localized the channel's selectivity determining sequence. Overexpression of Pex11 resulted in acceleration of fatty acids β-oxidation in intact cells but not in the corresponding lysates. The β-oxidation was affected in cells by expression of the Pex11 protein carrying point mutations in the selectivity determining sequence. These data suggest that the Pex11-dependent transmembrane traffic of metabolites may be a rate-limiting step in the β-oxidation of fatty acids. This conclusion was corroborated by analysis of the rate of β-oxidation in yeast strains expressing Pex11 with mutations mimicking constitutively phosphorylated (S165D, S167D) or unphosphorylated (S165A, S167A) protein. The results suggest that phosphorylation of Pex11 is a mechanism that can control the peroxisomal β-oxidation rate. Our results disclose an unexpected function of Pex11 as a non-selective channel responsible for transfer of metabolites across peroxisomal membrane. The data indicate that peroxins may be involved in peroxisomal metabolic processes in addition to their role in peroxisome biogenesis.

Hansenula polymorpha Pex37 is a peroxisomal membrane protein required for organelle fission and segregation

“…Methanol metabolism requires import of xylulose 5‐phosphate (230 Da) into peroxisomes, which apparently also does not require Pex37. Interestingly, a recent study in S. cerevisiae demonstrated that Pex11 forms a nonselective channel for the transfer of metabolites with size exclusion limit of 300–400 Da across the peroxisomal membrane . Hence, it is possible that Pex11 and Pex37 play redundant roles in metabolite transport, explaining why we did not observed growth defects for the pex37 mutant strain.…”

“…The broad range of peroxisomal metabolic pathways requires continuous metabolite exchange between the peroxisomal matrix and cytosol. So far, two pore‐forming proteins have been identified in peroxisomal membranes, namely mammalian PXMP2 and Saccharomyces cerevisiae Pex11 . Based on in vitro assays and biochemical studies, both proteins were proposed to enable free diffusion of molecules with molecular masses up to 300 Da.…”

Peroxisomes: versatile organelles with diverse roles in plants

“…Yeast Pex11 has a pore-forming function, but whether plant PEX11s also possess this function has not been reported (Mindthoff et al, 2016). Yeast Pex11 has a pore-forming function, but whether plant PEX11s also possess this function has not been reported (Mindthoff et al, 2016).…”

“…Non-selective peroxisomal membrane channels may allow the passage of small solutes, such as organic acids. Yeast Pex11 has a pore-forming function, but whether plant PEX11s also possess this function has not been reported (Mindthoff et al, 2016). Several additional peroxisomal membrane proteins, such as PMP22 (peroxisomal membrane protein of 22 kDa), CDC (Ca 2+ -dependent carrier) and SMP2 (short membrane protein 2), also have potential pore-forming activities (summarized in .…”

The novel peroxin Pex37: the Pxmp2 family joins the peroxisomal fission machinery

“…The idea that the Pxmp2 homolog Pex37 might potentially also have pore‐forming abilities is even more striking as also the other membrane protein factor required for peroxisomal fission, namely Pex11, can function as a nonselective channel as well in S. cerevisiae . Moreover, it has been assumed that Pxmp2 and Pex11β contribute to H 2 O 2 transport together with a yet unidentified channel in mammalian cells .…”