Novel mechanisms in nutrient activation of the yeast Protein Kinase A pathway

Thevelein, Johan M. and Monge Bonini, Beatriz and Castermans, Dries and Haesendonckx, Steven and Kriel, Johan and Louwet, Wendy and Thayumanavan, Palvannan and Popova, Yulia and Rubio-Texeira, Marta and Schepers, Wim and Vandormael, Patrick and Zeebroeck, Griet Van and Verhaert, Peter and Versele, Matthias and Voordeckers, Karin (2008) Novel mechanisms in nutrient activation of the yeast Protein Kinase A pathway. Acta Microbiologica et Immunologica Hungarica, 55 (2). pp. 75-89. ISSN 1217-8950

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Abstract

In yeast the Protein Kinase A (PKA) pathway can be activated by a variety of nutrients. Fermentable sugars, like glucose and sucrose, trigger a spike in the cAMP level, followed by activation of PKA and phosphorylation of target proteins causing a.o. mobilization of reserve carbohydrates, repression of stress-related genes and induction of growth-related genes. Glucose and sucrose are sensed by a G-protein coupled receptor system that activates adenylate cyclase and also activates a bypass pathway causing direct activation of PKA. Addition of other essential nutrients, like nitrogen sources or phosphate, to glucose-repressed nitrogen-or phosphate-starved cells, also triggers rapid activation of the PKA pathway. In these cases cAMP is not involved as a second messenger. Amino acids are sensed by the Gap1 transceptor, previously considered only as an amino acid transporter. Recent results indicate that the amino acid ligand has to induce a specific conformational change for signaling. The same amino acid binding site is involved in transport and signaling. Similar results have been obtained for Pho84 which acts as a transceptor for phosphate activation of the PKA pathway. Ammonium activation of the PKA pathway in nitrogen-starved cells is mediated mainly by the Mep2 transceptor, which belongs to a different class of transporter proteins. Hence, different types of sensing systems are involved in control of the yeast PKA pathway by nutrients.

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