Os04g0447800

Glutamate decarboxylase (GAD) converts L-glutamate to g-aminobutyric acid (GABA), which is a non-protein amino acid present in all organisms. Plant GADs carry a C-terminal extension that binds to Ca2+/calmodulin(CaM) to modulate enzyme activity.

Annotated Information

Function

• Plant GADs carry a C-terminal extension that binds to Ca2+/calmodulin(CaM) to modulate enzyme activity.Glutamate decarboxylase (GAD) is an enzyme that catalyses the conversion of L-glutamate to c-aminobutyric acid (GABA), which is a non-protein amino acid that is commonly present in both prokaryotes and eukaryotes. In animals, GABA is known to be a major inhibitory neurotransmitter.

Expression

• Recent sequencing of the rice genome revealed the presence of five GAD isoforms, including OsGAD1 and OsGAD2 (International Rice Genome Sequencing Project,2005). All five isoforms are at least transcriptionally active, given the presence of corresponding EST clones.Figure 1 shows the amino acid sequences of the C-terminal regions of the five rice GADs and the petunia GAD (PhGAD), which is currently the most intensively analysed GAD (Baum et al., 1993).

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• Data presented here show that the mutant GAD2 gene contributes to the extremely high level of GABA accumulated in cells. First, the mutant GAD2 enzyme had a much higher level of Ca2+/CaM-independent activity than the wild-type enzyme in vitro (Table. 1). Second,RT-PCR analysis indicated overexpression of the transgene at the RNA level (Fig. 5A). Third, western blot analysis using an anti-GAD2 antibody indicated a positive correlation between GAD2DC protein concentration and GABA accumulation (Fig. 5B).

Evolution

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Labs working on this gene

• Department of Biological Science, Shimane University, Nishikawatsu 1060, Matsue, Shimane 690-8504, Japan
• Transgenic Crop Research and Development Center, National Institute of Agrobiological Sciences,Kannondai 2-1-2, Tsukuba, Ibaraki 305-8602, Japan

References

• Akama K, Akihiro T, Kitagawa M, Takaiwa F. 2001. Rice(Oryza sativa) contains a novel isoform of glutamate decarboxylase that lacks an authentic calmodulin-binding domain at the C-terminus. Biochimica et Biophysica Acta 1522, 143–150.