PgmNr Y3018: GPH1 over-expression rescues glycogen and calcium accumulation defects in a pgm2∆ mutant strain of Saccharomyces cerevisiae.

Authors:
K. Ngo; A. Charales; R. McDonald; V. Bahram; A. Selvamani; D. Aiello


Institutes
Austin College, Sherman, TX.


Keyword: Cell Cycle/Growth Control/Metabolism

Abstract:

Phosphoglucomutase (PGM) plays an important role in yeast carbohydrate metabolism. It is responsible for interconverting glucose-1-phosphate (G1P) and glucose-6-phosphate (G6P). Pgm2 is the major isoform of PGM in Saccharomyces cerevisiae. Yeast that lack PGM2 exhibit slow growth, sensitivity to cyclosporine A, high glycogen accumulation, and calcium homeostasis defects when metabolizing galactose. The purpose of this investigation is to determine whether or not hyperaccumulation of glycogen contributes to other phenotypes observed in the pgm2Δ mutants. The high glycogen accumulation can be rescued using two different approaches: decreasing glycogen synthesis or increasing glycogen breakdown. To decrease glycogen synthesis, knockouts of the two known glycogen synthase enzymes, gsy1∆ and gsy2∆, were constructed in both wt and pgm2∆ strains, alone and in combination.  GPH1, encoding glycogen phosphorylase, was over-expressed to enhance glycogen breakdown in the context of the wt and pgm2∆ strains alone, and in combination with the gsy1∆ and gsy2∆ mutants. Gph1 is responsible for catalyzing the breakdown of glycogen to G1P. The growth, glycogen accumulation, and calcium accumulation phenotypes of each strain were analyzed. Glycogen accumulation was monitored by both iodine vapor staining and by quantitative enzymatic assay. Loss of either isoform of glycogen synthase (gsy1∆ or gsy2∆) failed to rescue pgm2∆ defects.  However, we report here that GPH1 over-expression partially rescues the pgm2Δ cyclosporine A growth defect when metabolizing galactose as a carbon source. Additionally, GPH1 over-expression rescues the high calcium and glycogen accumulation defects observed in pgm2∆ mutants.



Yeast Database Genetic Index
1. gene symbol: PGM2; systematic name: YMR105C
2. gene symbol: GSY1; systematic name: YFR015C
3. gene symbol: GSY2; systematic name: YLR258W
4. gene symbol: GPH1; systematic name: YPR160W