GABA transaminases from Saccharomyces cerevisiae and Arabidopsis thaliana complement function in cytosol and mitochondria

Yeast. 2013 Jul;30(7):279-89. doi: 10.1002/yea.2962. Epub 2013 Jun 21.

Abstract

GABA transaminase (GABA-T) catalyses the conversion of GABA to succinate semialdehyde (SSA) in the GABA shunt pathway. The GABA-T from Saccharomyces cerevisiae (ScGABA-TKG) is an α-ketoglutarate-dependent enzyme encoded by the UGA1 gene, while higher plant GABA-T is a pyruvate/glyoxylate-dependent enzyme encoded by POP2 in Arabidopsis thaliana (AtGABA-T). The GABA-T from A. thaliana is localized in mitochondria and mediated by an 18-amino acid N-terminal mitochondrial targeting peptide predicated by both web-based utilities TargetP 1.1 and PSORT. Yeast UGA1 appears to lack a mitochondrial targeting peptide and is localized in the cytosol. To verify this bioinformatic analysis and examine the significance of ScGABA-TKG and AtGABA-T compartmentation and substrate specificity on physiological function, expression vectors were constructed to modify both ScGABA-TKG and AtGABA-T, so that they express in yeast mitochondria and cytosol. Physiological function was evaluated by complementing yeast ScGABA-TKG deletion mutant Δuga1 with AtGABA-T or ScGABA-TKG targeted to the cytosol or mitochondria for the phenotypes of GABA growth defect, thermosensitivity and heat-induced production of reactive oxygen species (ROS). This study demonstrates that AtGABA-T is functionally interchangeable with ScGABA-TKG for GABA growth, thermotolerance and limiting production of ROS, regardless of location in mitochondria or cytosol of yeast cells, but AtGABA-T is about half as efficient in doing so as ScGABA-TKG. These results are consistent with the hypothesis that pyruvate/glyoxylate-limited production of NADPH mediates the effect of the GABA shunt in moderating heat stress in Saccharomyces.

Keywords: Arabidopsis; GABA transaminase; Saccharomyces; cytosol; mitochondria.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • 4-Aminobutyrate Transaminase / genetics
  • 4-Aminobutyrate Transaminase / metabolism*
  • Arabidopsis / enzymology*
  • Arabidopsis / genetics
  • Arabidopsis / physiology
  • Arabidopsis Proteins / genetics
  • Arabidopsis Proteins / metabolism*
  • Cytosol / enzymology*
  • Genetic Complementation Test
  • Glyoxylates / metabolism
  • Ketoglutaric Acids / metabolism
  • Mitochondria / enzymology*
  • Phenotype
  • Protein Sorting Signals
  • Protein Transport
  • Pyruvic Acid / metabolism
  • Reactive Oxygen Species / metabolism
  • Saccharomyces cerevisiae / enzymology*
  • Saccharomyces cerevisiae / genetics
  • Saccharomyces cerevisiae / physiology
  • Saccharomyces cerevisiae Proteins / genetics
  • Saccharomyces cerevisiae Proteins / metabolism*
  • Sequence Deletion
  • Transaminases / genetics
  • Transaminases / metabolism*

Substances

  • Arabidopsis Proteins
  • Glyoxylates
  • Ketoglutaric Acids
  • Protein Sorting Signals
  • Reactive Oxygen Species
  • Saccharomyces cerevisiae Proteins
  • Pyruvic Acid
  • Transaminases
  • 4-Aminobutyrate Transaminase
  • POP2 protein, Arabidopsis
  • UGA1 protein, S cerevisiae