title: Loss of the major isoform of phosphoglucomutase results in altered calcium homeostasis in Saccharomyces cerevisiae.
abstract: Phosphoglucomutase (PGM) is a key enzyme in glucose metabolism, where it catalyzes the interconversion of glucose 1-phosphate (Glc-1-P) and glucose 6-phosphate (Glc-6-P). In this study, we make the novel observation that PGM is also involved in the regulation of cellular Ca(2+) homeostasis in Saccharomyces cerevisiae. When a strain lacking the major isoform of PGM (pgm2Delta) was grown on media containing galactose as sole carbon source, its rate of Ca(2+) uptake was 5-fold higher than an isogenic wild-type strain. This increased rate of Ca(2+) uptake resulted in a 9-fold increase in the steady-state total cellular Ca(2+) level. The fraction of cellular Ca(2+) located in the exchangeable pool in the pgm2Delta strain was found to be as large as the exchangeable fraction observed in wild-type cells, suggesting that the depletion of Golgi Ca(2+) stores is not responsible for the increased rate of Ca(2+) uptake. We also found that growth of the pgm2Delta strain on galactose media is inhibited by 10 microM cyclosporin A, suggesting that activation of the calmodulin/calcineurin signaling pathway is required to activate the Ca(2+) transporters that sequester the increased cytosolic Ca(2+) load caused by this high rate of Ca(2+) uptake. We propose that these Ca(2+)-related alterations are attributable to a reduced metabolic flux between Glc-1-P and Glc-6-P due to a limitation of PGM enzymatic activity in the pgm2Delta strain. Consistent with this hypothesis, we found that this "metabolic bottleneck" resulted in an 8-fold increase in the Glc-1-P level compared with the wild-type strain, while the Glc-6-P and ATP levels were normal. These results suggest that Glc-1-P (or a related metabolite) may participate in the control of Ca(2+) uptake from the environment.
authors.affiliation: Department of Microbiology, University of Alabama at Birmingham, Birmingham, Alabama 35294, USA.
authors.forename: L
authors.initials: L
authors.lastname: Fu
authors.forename: A
authors.initials: A
authors.lastname: Miseta
authors.forename: D
authors.initials: D
authors.lastname: Hunton
authors.forename: R B
authors.initials: RB
authors.lastname: Marchase
authors.forename: D M
authors.initials: DM
authors.lastname: Bedwell
mesh_terms: D002118:Calcium / Q000493:pharmacokinetics*; D002268:Carboxypeptidases / Q000378:metabolism; D043402:Cathepsin A; D004721:Endoplasmic Reticulum / Q000378:metabolism; D005690:Galactose / Q000378:metabolism; D006026:Glycoside Hydrolases / Q000378:metabolism; D006031:Glycosylation; D006056:Golgi Apparatus / Q000378:metabolism; D016296:Mutagenesis; D010641:Phenotype; D010733:Phosphoglucomutase / Q000737:chemistry* / Q000235:genetics; D020033:Protein Isoforms; D012441:Saccharomyces cerevisiae / Q000201:enzymology*; D013997:Time Factors; D043324:beta-Fructofuranosidase
chemical_list: D020033:Protein Isoforms; D006026:Glycoside Hydrolases; D043324:beta-Fructofuranosidase; D002268:Carboxypeptidases; D043402:Cathepsin A; D010733:Phosphoglucomutase; D002118:Calcium; D005690:Galactose