Portal de Periódicos da CAPES

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

2008; Akadémiai Kiadó; Volume: 55; Issue: 2 Linguagem: Inglês

10.1556/amicr.55.2008.2.1

1588-2640

Johan M. Thevelein, Beatriz M. Bonini, Dries Castermans, Steven Haesendonckx, Johan Kriel, Wendy Louwet, Thayumanavan Palvannan, Yulia Popova, Marta Rubio‐Texeira, Wim Schepers, Patrick Vandormael, Griet Van Zeebroeck, Peter Verhaert, Matthias Versele, Karin Voordeckers,

Protein Kinase Regulation and GTPase Signaling

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.