The Ubiquitin Ligase Ubr11 Is Essential for Oligopeptide Utilization in the Fission Yeast Schizosaccharomyces pombe

Abstract

c Uptake of extracellular oligopeptides in yeast is mediated mainly by specific transporters of the peptide transporter (PTR) and oligopeptide transporter (OPT) families. Here, we investigated the role of potential peptide transporters in the yeast Schizosaccharomyces pombe. Utilization of naturally occurring dipeptides required only Ptr2/SPBC13A2.04c and none of the other 3 OPT proteins (Isp4, Pgt1, and Opt3), whereas only Isp4 was indispensable for tetrapeptide utilization. Both Ptr2 and Isp4 localized to the cell surface, but under rich nutrient conditions Isp4 localized in the Golgi apparatus through the function of the ubiquitin ligase Pub1. Furthermore, the ubiquitin ligase Ubr11 played a significant role in oligopeptide utilization. The mRNA levels of both the ptr2 and isp4 genes were significantly reduced in ubr11⌬ cells, and the dipeptide utilization defect in the ubr11⌬ mutant was rescued by the forced expression of Ptr2. Consistent with its role in transcriptional regulation of peptide transporter genes, the Ubr11 protein was accumulated in the nucleus. Unlike the situation in Saccharomyces cerevisiae, the oligopeptide utilization defect in the S. pombe ubr11⌬ mutant was not rescued by inactivation of the Tup11/12 transcriptional corepressors, suggesting that the requirement for the Ubr ubiquitin ligase in the upregulation of peptide transporter mRNA levels is conserved in both yeasts; however, the actual mechanism underlying the control appears to be different. We also found that the peptidomimetic proteasome inhibitor MG132 was still operative in a strain lacking all known PTR and OPT peptide transporters. Therefore, irrespective of its peptide-like structure, MG132 is carried into cells independently of the representative peptide transporters.

The type‐2 N‐end rule peptide recognition activity of Ubr11 ubiquitin ligase is required for the expression of peptide transporters

“…Amount of Pk‐Ubr11‐m4 and ‐m5 proteins may be lower than others, but this is not conclusive because of the low expression levels of the endogenous Ubr11 protein (our unpublished results) and difficulty to prevent non‐specific proteolysis during sample preparation. Interestingly, all five ubr11 mutants failed to utilize dipeptides, as was previously reported for a ubr11Δ strain [12], regardless of whether the dipeptides were type‐1 (Lys‐Leu, Fig. 4A) or type‐2 (Leu‐Ala and Tyr‐Leu, data not shown).…”

“…The only physiological defect in the S. pombe ubr11 mutant known so far is the unavailability of extracellular peptides [12]. All five ubr11 mutants examined in this study failed to utilize peptides due to insufficient expression of peptide transporter genes.…”

“…1). Although Ubr ubiquitin ligase is essential for peptide transporter expression in both S. pombe and S. cerevisiae , regulation seems to be different between the two yeasts [12]. In particular, an apparent homolog of Cup9, which is a target substrate of Ubr1 for peptide utilization in S. cerevisiae , is not encoded in the S. pombe genome.…”

Functional Implications and Ubiquitin-Dependent Degradation of the Peptide Transporter Ptr2 in Saccharomyces cerevisiae

“…PTR2 has been analyzed extensively with respect to transcriptional regulation in S. cerevisiae (45)(46)(47) and Schizosaccharomyces pombe (48). Peptide import is upregulated by growth media containing poor nitrogen sources such as allantoin, isoleucine, or proline due to upregulation of PTR2 transcription (49).…”

Expression profiling and functional analyses of BghPTR2, a peptide transporter from Blumeria graminis f. sp. hordei

“…Nucleotide and amino acid sequence data of BghPTR2 is available in the GenBank/ EMBL/DDBJ databases under accession numbers AJ938049 and CAI79386.2 and Bgh05050 in the CDS sequences of BluGen database. The phylogenetic tree was constructed on the basis of BghPTR2, 17 PTR2s with highest similarity to BghPTR2 and nine fungal PTR2's described in the literature, including PTRs from Candida albicans (Basrai et al 1995;Dunkel et al 2013), Schizosaccharomyces pombe (Kitamura et al 2012), Stagonospora nodorum (Solomon et al 2003), Hebeloma cylindrosporum (Benjdia et al 2006), Trichoderma harzianum (Vizcaino et al 2006), Saccharomyces cerevisiae (Perry et al 1994) and Rhizophagus irregularis (Belmondo et al 2014). The neighbor joining method in the CLC Bio workbench was used.…”