Novel mechanisms in nutrient activation of the yeast protein kinase A pathway.
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.
Thevelein
Johan M
JM
Laboratory of Molecular Cell Biology, Institute of Botany and Microbiology, Katholieke Universiteit Leuven, Belgium. johan.thevelein@bio.kuleuven.be
Bonini
Beatriz Monge
BM
Castermans
Dries
D
Haesendonckx
Steven
S
Kriel
Johan
J
Louwet
Wendy
W
Thayumanavan
Palvannan
P
Popova
Yulia
Y
Rubio-Texeira
Marta
M
Schepers
Wim
W
Vandormael
Patrick
P
Van Zeebroeck
Griet
G
Verhaert
Peter
P
Versele
Matthias
M
Voordeckers
Karin
K
D017868:Cyclic AMP-Dependent Protein Kinases / Q000378:metabolism*; D005502:Food; D005656:Fungal Proteins; D012440:Saccharomyces / Q000502:physiology*; D015398:Signal Transduction
D005656:Fungal Proteins; D017868:Cyclic AMP-Dependent Protein Kinases