The tetratricopeptide repeat domains of human, tobacco, and nematode PEX5 proteins are functionally interchangeable with the analogous native domain for peroxisomal import of PTS1-terminated proteins in yeast

Abstract

In the yeast Saccharomyces cerevisiae, beta-oxidation of fatty acids is compartmentalised in peroxisomes. Most yeast peroxisomal matrix proteins contain a type 1C-terminal peroxisomal targeting signal (PTS1) consisting of the tripeptide SKL or a conservative variant thereof. PTS1-terminated proteins are imported by Pex5p, which interacts with the targeting signal via a tetratricopeptide repeat (TPR) domain. Yeast cells devoid of Pex5p are unable to import PTS1-containing proteins and cannot degrade fatty acids. Here, the PEX5-TPR domains from human, tobacco, and nematode were inserted into a TPR-less yeast Pex5p construct to generate Pex5p chimaeras. These hybrid proteins were examined for functional complementation of the pex5delta mutant phenotype. Expression of the Pex5p chimaeras in pex5delta mutant cells restored peroxisomal import of PTS1-terminated proteins. Chimaera expression also re-established degradation of oleic acid, allowing growth on this fatty acid as a sole carbon source. We conclude that, in the context of Pex5p chimaeras, the human, tobacco, and nematode Pex5p-TPR domains are functionally interchangeable with the native domain for the peroxisomal import of yeast proteins terminating with canonical PTS1s. Non-conserved yeast PTS1s, such as HRL and HKL, did not interact with the tobacco PEX5-TPR domain in the two-hybrid system. HRL occurs at the C-terminus of the peroxisomal protein Eci1p, which is required for growth on unsaturated fatty acids. Although mutant pex5delta cells expressing a yeast/tobacco Pex5p chimaera failed to import a GFP-Eci1p reporter protein, they were able to grow on oleic acid. We reason that this is due to a cryptic PTS in native Eci1p that can function in a redundant system with the C-terminal HRL.

Genome-wide analysis of the U-box E3 ligases gene family in potato (Solanum tuberosum L.) and overexpress StPUB25 enhance drought tolerance in transgenic Arabidopsis

“…Tetrapeptide repeat (TPR) motifs are protein–protein interaction modules that are present many functionally diverse proteins and contribute to specific interactions with chaperone proteins [ 54 , 55 ]. Previous studies found that AtCHIP (AT3G07370) interacts with molecular chaperones such as Hsc70 through its TPRs and may therefore regulate the switch from molecular chaperon-assisted protein folding to proteasomal degradation.…”

Ubiquitin-conjugating activity by PEX4 is required for efficient protein transport to peroxisomes in Arabidopsis thaliana

“…PEROXIN ( PEX ) genes are responsible for peroxisome biogenesis, including protein transport from yeast, mammalian cultured cells, and plants ( 13 , 14 , 15 , 16 , 17 , 18 , 19 ). PEX5 and PEX7 function as the PTS1 and PTS2 receptors, respectively, in yeast ( 20 , 21 ), mammals ( 22 , 23 ), and plants ( 24 , 25 , 26 , 27 , 28 , 29 , 30 ). These receptors recognize PTS1 or PTS2, bind to them in the cytosol, and direct them to the transport machinery consisting of PEX14 ( 31 ), PEX12 ( 16 , 32 ), PEX13 ( 16 , 32 ), and other unidentified factors on the peroxisomal membrane.…”