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

In the yeast Saccharomyces cerevisiae, beta -oxidation of fatty acids is co mpartmentalised in peroxisomes. Nest yeast peroxisomal matrix proteins cont ain a type 1 C-terminal peroxisomal targeting signal (PTS1) consisting of t he tripeptide SKL or a conservative variant thereof. PTS1-terminated protei ns are imported by Pex5p, which interacts with the targeting signal via a t etratricopeptide repeat (TPR) domain. Yeast cells devoid of Pex5p are unabl e 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 p roteins were examined for functional complementation of the pex5 Delta muta nt phenotype. Expression of the Pex5p chimaeras in pex5 Delta mutant cells restored peroxisomal import of PTS1-terminated proteins. Chimaera expressio n also re-established degradation of oleic acid, allowing growth on this fa tty acid as a sole carbon source. We conclude that, in the context of Pex5p chimaeras, the human, tobacco, and nematode Pex5p-TPR domains are function ally interchangeable with the native domain for the peroxisomal import of y east 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 prot ein Eci Ip, which is required for growth on unsaturated fatty acids, Althou gh mutant pex5 Delta cells expressing a yeast/tobacco Pex5p chimaera failed to import a GFP-Eci1p reporter protein, they were able to grow on oleic ac id. We reason that this is due to a cryptic PTS in native Eci1p that can fu nction in a redundant system with the C-terminal HRL.