title: Characterization of glutamate decarboxylase from Synechocystis sp. PCC6803 and its role in nitrogen metabolism.
abstract: Glutamate decarboxylase (GAD) (EC 4.1.1.15), an enzyme responsible for the synthesis of γ-aminobutyric acid (GABA), from Synechocystis sp. PCC6803 was cloned and overexpressed in Escherichia coli BL21(DE3). The purified enzyme was expressed as a monomeric protein with a molecular mass of 53 and 55 kDa as determined by SDS-PAGE and gel filtration chromatography, respectively. The enzyme activity was pyridoxal-5'-phosphate dependent with an optimal activity at pH 6.0 and 30 °C. The catalytic properties of this enzyme were, Km = 19.6 mM; kcat = 100.7 s(-1); and kcat/Km = 5.1 mM(-1) s(-1). The transcription levels of genes involved in nitrogen metabolism were up-regulated in the Δgad strain. The mutant showed approximately 4- and 8-fold increases in the transcript levels of kgd and gabdh encoding a novel α-ketoglutarate decarboxylase and γ-aminobutanal dehydrogenase, respectively. Overall results suggested that in Synechocystis lacking a functional GAD, the γ-aminobutanal dehydrogenase might serve as an alternative catalytic pathway for GABA synthesis.
authors.affiliation: Laboratory of Cyanobacterial Biotechnology, Department of Biochemistry, Faculty of Science, Chulalongkorn University, Bangkok, 10330, Thailand.
authors.forename: Simab
authors.initials: S
authors.lastname: Kanwal
authors.affiliation: Laboratory of Cyanobacterial Biotechnology, Department of Biochemistry, Faculty of Science, Chulalongkorn University, Bangkok, 10330, Thailand. Electronic address: aran.i@chula.ac.th.
authors.forename: Aran
authors.initials: A
authors.lastname: Incharoensakdi
mesh_terms: D002384:Catalysis; D015964:Gene Expression Regulation, Bacterial; D005798:Genes, Bacterial / Q000235:genetics; D005968:Glutamate Decarboxylase / Q000235:genetics / Q000378:metabolism*; D009584:Nitrogen / Q000378:metabolism*; D046939:Synechocystis / Q000201:enzymology* / Q000235:genetics / Q000378:metabolism
chemical_list: D005968:Glutamate Decarboxylase; D009584:Nitrogen
keywords: GABA metabolism; Glutamate decarboxylase; Synechocystis; Transcription; Δgad strain