Ammonium permease-based sensing mechanism for rapid ammonium activation of the protein kinase A pathway in yeast.
In the yeast Saccharomyces cerevisiae starvation for nitrogen on a glucose-containing medium causes entrance into G0 and downregulation of all targets of the PKA pathway. Re-addition of a nitrogen source in the presence of glucose causes rapid activation of trehalase and other PKA targets. Trehalase activation upon ammonium re-supplementation is dependent on PKA activity, but not on its regulatory subunit nor is it associated with an increase in cAMP. In nitrogen-starved cells, ammonium transport and activation of trehalase are most active in strains expressing either the Mep2 or Mep1 ammonium permease, as opposed to Mep3. The non-metabolizable ammonium analogue, methylamine, also triggers activation of trehalase when transported by Mep2 but not when taken up by diffusion. Inhibition of ammonium incorporation into metabolism did not prevent signalling. Extensive site-directed mutagenesis of Mep2 showed that transport and signalling were generally affected in a similar way, although they could be separated partially by specific mutations. Our results suggest an ammonium permease-based sensing mechanism for rapid activation of the PKA pathway. Mutagenesis of Asn246 to Ala in Mep2 abolished transport and signalling with methylamine but had no effect with ammonium. The plant AtAmt1;1, AtAmt1;2, AtAmt1;3 and AtAmt2 ammonium transporters sustained transport and trehalase activation to different extents. Specific mutations in Mep2 affected the activation of trehalase differently from induction of pseudohyphal differentiation. We also show that Mep permease involvement in PKA control is different from their role in haploid invasive growth, in which Mep1 sustains and Mep2 inhibits, in a way independent of the ammonium level in the medium.
Van Nuland
An
A
Laboratory of Molecular Cell Biology, Institute of Botany and Microbiology, Katholieke Universiteit Leuven, Kasteelpark Arenberg 31, B-3001 Leuven-Heverlee, Flanders, Belgium.
Vandormael
Patrick
P
Donaton
Monica
M
Alenquer
Marta
M
Lourenço
Artur
A
Quintino
Edgar
E
Versele
Matthias
M
Thevelein
Johan M
JM
D000595:Amino Acid Sequence; D001692:Biological Transport; D027682:Cation Transport Proteins / Q000235:genetics / Q000378:metabolism*; D000242:Cyclic AMP / Q000378:metabolism; D017868:Cyclic AMP-Dependent Protein Kinases / Q000378:metabolism*; D004171:Diploidy; D006238:Haploidy; D008744:Methylamines / Q000378:metabolism; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D009154:Mutation; D010940:Plant Proteins / Q000378:metabolism; D000644:Quaternary Ammonium Compounds / Q000378:metabolism* / Q000494:pharmacology; D012441:Saccharomyces cerevisiae / Q000187:drug effects / Q000235:genetics / Q000378:metabolism*; D029701:Saccharomyces cerevisiae Proteins / Q000235:genetics / Q000378:metabolism*; D015398:Signal Transduction
D027682:Cation Transport Proteins; C088951:MEP1 protein, S cerevisiae; C107270:MEP2 protein, S cerevisiae; D008744:Methylamines; D010940:Plant Proteins; D000644:Quaternary Ammonium Compounds; D029701:Saccharomyces cerevisiae Proteins; C088952:ammonium transporters, plant; C027451:methylamine; D000242:Cyclic AMP; D017868:Cyclic AMP-Dependent Protein Kinases