title: GABA transaminases from Saccharomyces cerevisiae and Arabidopsis thaliana complement function in cytosol and mitochondria.
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.
authors.affiliation: Department of Biological Sciences, Auburn University, Auburn, AL 36849, USA.
authors.forename: Juxiang
authors.initials: J
authors.lastname: Cao
authors.forename: Jose M
authors.initials: JM
authors.lastname: Barbosa
authors.forename: Narendra
authors.initials: N
authors.lastname: Singh
authors.forename: Robert D
authors.initials: RD
authors.lastname: Locy
mesh_terms: D000612:4-Aminobutyrate Transaminase / Q000235:genetics / Q000378:metabolism*; D017360:Arabidopsis / Q000201:enzymology* / Q000235:genetics / Q000502:physiology; D029681:Arabidopsis Proteins / Q000235:genetics / Q000378:metabolism*; D003600:Cytosol / Q000201:enzymology*; D005816:Genetic Complementation Test; D006038:Glyoxylates / Q000378:metabolism; D007656:Ketoglutaric Acids / Q000378:metabolism; D008928:Mitochondria / Q000201:enzymology*; D010641:Phenotype; D021382:Protein Sorting Signals; D021381:Protein Transport; D019289:Pyruvic Acid / Q000378:metabolism; D017382:Reactive Oxygen Species / Q000378:metabolism; D012441:Saccharomyces cerevisiae / Q000201:enzymology* / Q000235:genetics / Q000502:physiology; D029701:Saccharomyces cerevisiae Proteins / Q000235:genetics / Q000378:metabolism*; D017384:Sequence Deletion; D000637:Transaminases / Q000235:genetics / Q000378:metabolism*
chemical_list: D029681:Arabidopsis Proteins; D006038:Glyoxylates; D007656:Ketoglutaric Acids; D021382:Protein Sorting Signals; D017382:Reactive Oxygen Species; D029701:Saccharomyces cerevisiae Proteins; D019289:Pyruvic Acid; D000637:Transaminases; D000612:4-Aminobutyrate Transaminase; C489779:POP2 protein, Arabidopsis; C558424:UGA1 protein, S cerevisiae
keywords: Arabidopsis; GABA transaminase; Saccharomyces; cytosol; mitochondria