Nutrient transceptors physically interact with the yeast S6/protein kinase B homolog, Sch9, a TOR kinase target

Zhiqiang Zhang,Ines Cottignie,Griet Van Zeebroeck,Johan M Thevelein

doi:10.1042/bcj20200722

Zhiqiang Zhang, Ines Cottignie + Show 2 more

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https://doi.org/10.1042/bcj20200722

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Abstract

Multiple starvation-induced, high-affinity nutrient transporters in yeast function as receptors for activation of the protein kinase A (PKA) pathway upon re-addition of their substrate. We now show that these transceptors may play more extended roles in nutrient regulation. The Gap1 amino acid, Mep2 ammonium, Pho84 phosphate and Sul1 sulfate transceptors physically interact in vitro and in vivo with the PKA-related Sch9 protein kinase, the yeast homolog of mammalian S6 protein kinase and protein kinase B. Sch9 is a phosphorylation target of TOR and well known to affect nutrient-controlled cellular processes, such as growth rate. Mapping with peptide microarrays suggests specific interaction domains in Gap1 for Sch9 binding. Mutagenesis of the major domain affects the upstart of growth upon the addition of L-citrulline to nitrogen-starved cells to different extents but apparently does not affect in vitro binding. It also does not correlate with the drop in L-citrulline uptake capacity or transceptor activation of the PKA target trehalase by the Gap1 mutant forms. Our results reveal a nutrient transceptor–Sch9–TOR axis in which Sch9 accessibility for phosphorylation by TOR may be affected by nutrient transceptor–Sch9 interaction under conditions of nutrient starvation or other environmental challenges.

Highlights

The ability of yeast cells to sense nutrients and respond appropriately to their availability is crucial for real-time adaptation and survival in changing environments and for competition with other organisms
No Bimolecular fluorescence complementation (BiFC) signal could be observed in the cells during exponential growth (Supplementary Figure S1A), because of the repression of nutrient transceptor expression in the complete growth medium
To induce high expression of the respective nutrient transceptors, the cells were first grown to exponential phase after which they were starved for the substrate of the transceptor, as previously described [8,9,11,13]

Summary

Introduction

The ability of yeast cells to sense nutrients and respond appropriately to their availability is crucial for real-time adaptation and survival in changing environments and for competition with other organisms. Yeast cells have a wide array of nutrient-sensing systems for rapid adaptation to changes in the nutrient supply, including several types of plasma membrane nutrient sensors [1]. We have previously identified several high-affinity transporters that are strongly induced upon starvation for their substrate and display an additional receptor capacity, functioning as transporter-receptors or ‘transceptors’ They function in short-term activation of the protein kinase A (PKA) pathway [5] in nutrient-starved cells upon re-addition of their missing substrate: Gap for amino acids [6,7,8], Mep for ammonium [9], Pho for phosphate [10,11,12], Sul1/Sul for sulfate [13], Ftr for iron and Zrt for zinc [14]. Transceptors have been identified in other organisms but they generally regulate the transport and/or metabolism of the nutrient substrate of the transceptor, at least as far as is known [16]

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