title: The Saccharomyces cerevisiae PHM8 gene encodes a soluble magnesium-dependent lysophosphatidic acid phosphatase.
abstract: Phosphate is the essential macronutrient required for the growth of all organisms. In Saccharomyces cerevisiae, phosphatases are up-regulated, and the level of lysophosphatidic acid (LPA) is drastically decreased under phosphate-starved conditions. The reduction in the LPA level is attributed to PHM8, a gene of unknown function. phm8Delta yeast showed a decreased LPA-hydrolyzing activity under phosphate-limiting conditions. Overexpression of PHM8 in yeast resulted in an increase in the LPA phosphatase activity in vivo. In vitro assays of the purified recombinant Phm8p revealed magnesium-dependent LPA phosphatase activity, with maximal activity at pH 6.5. The purified Phm8p did not hydrolyze any lipid phosphates other than LPA. In silico analysis suggest that Phm8p is a soluble protein with no transmembrane domain. Site-directed mutational studies revealed that aspartate residues in a DXDXT motif are important for the catalysis. These findings indicated that LPA plays a direct role in phosphate starvation. This is the first report of the identification and characterization of magnesium-dependent soluble LPA phosphatase.
authors.affiliation: Lipid Laboratory, Department of Biochemistry, Indian Institute of Science, Bangalore 560012, India.
authors.forename: Venky Sreedhar
authors.initials: VS
authors.lastname: Reddy
authors.forename: Arjun Kumar
authors.initials: AK
authors.lastname: Singh
authors.forename: Ram
authors.initials: R
authors.lastname: Rajasekharan
mesh_terms: D020816:Amino Acid Motifs / Q000502:physiology; D017353:Gene Deletion; D006863:Hydrogen-Ion Concentration; D006868:Hydrolysis; D008246:Lysophospholipids / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D008274:Magnesium / Q000737:chemistry / Q000378:metabolism*; D016297:Mutagenesis, Site-Directed; D010710:Phosphates / Q000378:metabolism; D010744:Phosphoric Monoester Hydrolases / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D017434:Protein Structure, Tertiary / Q000502:physiology; D012441:Saccharomyces cerevisiae / Q000201:enzymology* / Q000235:genetics; D029701:Saccharomyces cerevisiae Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*
chemical_list: D008246:Lysophospholipids; D010710:Phosphates; D029701:Saccharomyces cerevisiae Proteins; C076020:lysophosphatidic acid phosphatase; D010744:Phosphoric Monoester Hydrolases; D008274:Magnesium; C032881:lysophosphatidic acid