Ppn2 endopolyphosphatase overexpressed in Saccharomyces cerevisiae: Comparison with Ppn1, Ppx1, and Ddp1 polyphosphatases

Abstract

Saccharomyces cerevisiae has high level of inorganic polyphosphate and a multicomponent system of its metabolism, including polyphosphatases Ppx1, Ppn1, Ddp1, and Ppn2. The aim of the study was to construct the yeast strain overexpressing Ppn2 and to compare the properties of Ppn2, Ppx1, Ppn1, and Ddp1 purified from overexpressing strains of S. cerevisiae. We overexpressed Ppn2 in S. cerevisiae under a strong constitutive promoter of the yeast glyceraldehyde-3-phosphate dehydrogenase-encoding gene and suggested biochemical criteria for distinguishing among yeast polyphosphatases, which is important for their identification and understanding of their functions. Ppn2, Ppn1, and Ddp1 had endopolyphosphatase activities, whereas Ppx1 did not. Ppx1 and Ppn1 exhibited high and Ddp1 and Ppn2 low exopolyphosphatase activity: 240, 500, 0.05 and 0.1 U/mg protein, respectively. The enzymes had distinct patterns of exopolyphosphatase activities stimulation by divalent metal ions. Ppn2, Ppn1 and Ddp1 displayed endopolyphosphatase activity in the presence of 1 mM Mg²⁺. The endopolyphosphatase activities of Ppn2 and Ppn1 were induced by 0.01 mM of Co²⁺ or Zn²⁺, whereas that of Ddp1 required 0.1 mM of these cations. The endopolyphosphatase activity of Ppn1 was inhibited by 0.01 mg mL^-1 of heparin, while endopolphosphatase activity of Ppn2 was weakly sensitive to 0.25 mg mL^-1 of heparin. The Ppx1 and Ppn1 activity with guanosine tetraphosphate was nearly 80% of activity with long-chain polyphosphates. The Ppn1 hydrolyzed dATP, while Ppx1 did not. The differences in the mode of polyphosphate hydrolysis, substrate specificity, metal ion dependence and cell localization suggest distinct roles of these enzymes in yeast.

Keywords: Divalent metal ions; Guanosine tetraphosphate; Polyphosphatase; Polyphosphate; Saccharomyces cerevisiae; dATP.