title: Nutrient control of yeast PKA activity involves opposing effects on phosphorylation of the Bcy1 regulatory subunit.
abstract: GPB1 and GPB2 encode kelch repeat-containing proteins that regulate protein kinase A (PKA) in yeast by a cAMP-independent process. Here we show that Gpb1 and Gpb2 stimulate phosphorylation of PKA regulatory subunit Bcy1 in low glucose concentrations, thereby promoting the inhibitory function of Bcy1 when nutrients are scarce and PKA activity is expected to be low. Gpb1 and Gpb2 stimulate Bcy1 phosphorylation at an unknown site, and this modification stabilizes Bcy1 that has been phosphorylated by PKA catalytic subunits at serine-145. The BCY1(S145A) mutation eliminates the effect of gpb1Δ gpb2Δ on Bcy1 stability but maintains their effect on phosphorylation and signaling, indicating that modulation of PKA activity by Gpb1 and Gpb2 is not solely due to increased levels of Bcy1. Inhibition of PKA catalytic subunits that are ATP analog-sensitive causes increased Bcy1 phosphorylation at the unknown site in high glucose. When PKA is inhibited, gpb1Δ gpb2Δ mutations have no effect on Bcy1 phosphorylation. Therefore, Gpb1 and Gpb2 oppose PKA activity by blocking the ability of PKA to inhibit Bcy1 phosphorylation at a site other than serine-145. Stimulation of Bcy1 phosphorylation by Gpb1 and Gpb2 produces a form of Bcy1 that is more stable and is a more effective PKA inhibitor.
authors.affiliation: Department of Pharmacology and Systems Therapeutics, Mount Sinai School of Medicine, New York, NY 10029, USA.
authors.forename: Roli
authors.initials: R
authors.lastname: Budhwar
authors.forename: Ailan
authors.initials: A
authors.lastname: Lu
authors.forename: Jeanne P
authors.initials: JP
authors.lastname: Hirsch
mesh_terms: D048868:Adaptor Proteins, Signal Transducing / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D020134:Catalytic Domain; D017868:Cyclic AMP-Dependent Protein Kinases / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D047908:Intracellular Signaling Peptides and Proteins / Q000378:metabolism; D010766:Phosphorylation; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism; D012441:Saccharomyces cerevisiae / Q000201:enzymology* / Q000235:genetics; D029701:Saccharomyces cerevisiae Proteins / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D015003:Yeasts / Q000201:enzymology* / Q000235:genetics / Q000378:metabolism; D018631:ras Proteins / Q000378:metabolism
chemical_list: D048868:Adaptor Proteins, Signal Transducing; C476991:GPB1 protein, S cerevisiae; C476990:Gpb2 protein, S cerevisiae; D047908:Intracellular Signaling Peptides and Proteins; D029701:Saccharomyces cerevisiae Proteins; D017346:Protein Serine-Threonine Kinases; C062391:YAK1 protein, S cerevisiae; D017868:Cyclic AMP-Dependent Protein Kinases; C489015:RAS2 protein, S cerevisiae; D018631:ras Proteins
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