Partial purification of Drosophila glutamate decarboxylase

Unraveling the Potential of γ-Aminobutyric Acid: Insights into Its Biosynthesis and Biotechnological Applications

γ-Aminobutyric acid (GABA) is a widely distributed non-protein amino acid that serves as a crucial inhibitory neurotransmitter in the brain, regulating various physiological functions. As a result of its potential benefits, GABA has gained substantial interest in the functional food and pharmaceutical industries. The enzyme responsible for GABA production is glutamic acid decarboxylase (GAD), which catalyzes the irreversible decarboxylation of glutamate. Understanding the crystal structure and catalytic mechanism of GAD is pivotal in advancing our knowledge of GABA production. This article provides an overview of GAD's sources, structure, and catalytic mechanism, and explores strategies for enhancing GABA production through fermentation optimization, metabolic engineering, and genetic engineering. Furthermore, the effects of GABA on the physiological functions of animal organisms are also discussed. To meet the increasing demand for GABA, various strategies have been investigated to enhance its production, including optimizing fermentation conditions to facilitate GAD activity. Additionally, metabolic engineering techniques have been employed to increase the availability of glutamate as a precursor for GABA biosynthesis. By fine-tuning fermentation conditions and utilizing metabolic and genetic engineering techniques, it is possible to achieve higher yields of GABA, thus opening up new avenues for its application in functional foods and pharmaceuticals. Continuous research in this field holds immense promise for harnessing the potential of GABA in addressing various health-related challenges.

Activity and coexpression of Drosophila black with ebony in fly optic lobes reveals putative cooperative tasks in vision that evade electroretinographic detection

Drosophila mutants black and ebony show pigmentation defects in the adult cuticle, which disclose their cooperative activity in β-alanyl-dopamine formation. In visual signal transduction, Ebony conjugates β-alanine to histamine, forming β-alanyl-histamine or carcinine. Mutation of ebony disrupts signal transduction and reveals an electroretinogram (ERG) phenotype. In contrast to the corresponding cuticle phenotype of black and ebony, there is no ERG phenotype observed when black expression is disrupted. This discrepancy calls into question the longstanding assumption of Black and Ebony interaction. The purpose of this study was to investigate the role of Black and Ebony in fly optic lobes. We excluded a presynaptic histamine uptake pathway and confirmed histamine recycling via carcinine formation in glia. β-Alanine supply for this pathway is independent of enzymatic synthesis by Black and β-alanine synthase Pyd3. Two versions of Black are expressed in vivo. Black is a specific aspartate decarboxylase with no activity on glutamate. RNA in situ hybridization and anti-Black antisera localized Black expression in the head. Immunolabeling revealed expression in lamina glia, in large medulla glia, in glia of the ocellar ganglion, and in astrocyte-like glia below the ocellar ganglion. In these glia types, Black expression is strictly accompanied by Ebony expression. Activity, localization, and strict coexpression with Ebony strongly indicate a specific mode of functional interaction that, however, evades ERG detection.

Glutamate decarboxylase of the parasitic arthropods Ctenocephalides felis and Rhipicephalus microplus: gene identification, cloning, expression, assay development, identification of inhibitors by high throughput screening and comparison with the orthologs from Drosophila melanogaster and mouse

Glutamate decarboxylase (l-glutamate 1-carboxylyase, E.C. 4.1.1.15, GAD) is the rate-limiting enzyme for the production of γ-aminobutyric acid (GABA), the major inhibitory neurotransmitter in vertebrates and invertebrates. We report the identification, isolation and characterization of cDNAs encoding GAD from the parasitic arthropods Ctenocephalides felis (cat flea) and Rhipicephalus microplus (cattle tick). Expression of the parasite GAD genes and the corresponding Drosophila melanogaster (fruit fly) GAD1 as well as the mouse GAD(65) and GAD(67) genes in Escherichia coli as maltose binding protein fusions resulted in functional enzymes in quantities compatible with the needs of high throughput inhibitor screening (HTS). A novel continuous coupled spectrophotometric assay for GAD activity based on the detection cascade GABA transaminase/succinic semialdehyde dehydrogenase was developed, adapted to HTS, and a corresponding screen was performed with cat flea, cattle tick and fruit fly GAD. Counter-screening of the selected 38 hit substances on mouse GAD(65) and GAD(67) resulted in the identification of non-specific compounds as well as inhibitors with preferences for arthropod GAD, insect GAD, tick GAD and the two mouse GAD forms. Half of the identified hits most likely belong to known classes of GAD inhibitors, but several substances have not been described previously as GAD inhibitors and may represent lead optimization entry points for the design of arthropod-specific parasiticidal compounds.

An examination of aspartate decarboxylase and glutamate decarboxylase activity in mosquitoes

A major pathway of beta-alanine synthesis in insects is through the alpha-decarboxylation of aspartate, but the enzyme involved in the decarboxylation of aspartate has not been clearly defined in mosquitoes and characterized in any insect species. In this study, we expressed two putative mosquito glutamate decarboxylase-like enzymes of mosquitoes and critically analyzed their substrate specificity and biochemical properties. Our results provide clear biochemical evidence establishing that one of them is an aspartate decarboxylase and the other is a glutamate decarboxylase. The mosquito aspartate decarboxylase functions exclusively on the production of beta-alanine with no activity with glutamate. Likewise the mosquito glutamate decarboxylase is highly specific to glutamate with essentially no activity with aspartate. Although insect aspartate decarboxylase shares high sequence identity with glutamate decarboxylase, we are able to closely predict aspartate decarboxylase from glutamate decarboxylase based on the difference of their active site residues.

Molecular cloning, partial genomic structure and functional characterization of succinic semialdehyde dehydrogenase genes from the parasitic insects Lucilia cuprina and Ctenocephalides felis

The enzyme succinic semialdehyde dehydrogenase (SSADH; EC1.2.1.24) is a component of the gamma-aminobutyric acid degradation pathway in mammals and is essential for development and function of the nervous system. Here we report the identification, cDNA cloning and functional expression of SSADH from the parasitic insects Lucilia cuprina and Ctenocephalides felis. The recombinant proteins possess potent NAD+-dependent SSADH activity, while their catalytic efficiency for other aldehyde substrates is lower. A genomic copy of the L. cuprina SSADH gene contains two introns, while a genomic gene version of C. felis is devoid of introns. In contrast to the single copy SSADH genes in Drosophila melanogaster and mammals, in L. cuprina and C. felis, multiple SSADH gene copies are present in the genome.

The Drosophila black enigma: the molecular and behavioural characterization of the black1 mutant allele

The cuticular melanization phenotype of black flies is rescued by beta-alanine, but beta-alanine production, by aspartate decarboxylation, was reported to be normal in assays of black mutants, and although black/Dgad2 is expressed in the lamina, the first optic ganglion, no electroretinogram (ERG) or other visual defect has been demonstrated in black flies. The purpose of this study was to investigate the black gene, and protein, in black(1) mutants of Drosophila melanogaster in order to resolve the apparent paradox of the black phenotype. Using black(1) mutant flies we show that (1) aspartate decarboxylase activity is significantly reduced in adults and at puparium formation, consistent with defects in cuticular and non-cuticular processes, (2) that the black(1) mutation is a frameshift, and black(1) flies are nulls for the black/DGAD2 protein, and (3) that behavioural experiments using Buridan's paradigm, demonstrate that black responds abnormally to visual cues. No ERG, or target recognition defects can be demonstrated suggesting a problem with higher order visual functions in black mutants.

A neural gene from Drosophila melanogaster with homology to vertebrate and invertebrate glutamate decarboxylases

Cross-species hybridization has been used to isolate a second Drosophila gene, with homology to a feline glutamate decarboxylase (Gad) cDNA. The gene differs in sequence, chromosomal location, and spatial expression from the previously reported Drosophila Gad gene, but both encode proteins of 58 kDa. The derived amino acid sequence reveals a typical pyridoxal phosphate binding site and sequence homology consistent with a glutamate decarboxylase function. The protein includes an amino-terminal polyasparagine sequence, and a beta-pleated sheet region, with regularly spaced glutamine and arginine residues, not found in other decarboxylases. Expression in the adult is limited to the neuropil of the first optic ganglion and to regions of the thoracic musculature that may correspond to the location of motor neuron axons. This is consistent with a glial localization for the transcript. There is no overlap with the reported expression of Drosophila Gad. Although the molecular evidence suggests that this gene encodes a pyridoxal phosphate-dependent decarboxylase, glutamate decarboxylase activity associated with this gene could not be demonstrated, and the in vivo substrate is unknown. It is possible that the protein encoded by this gene is novel, not only in sequence and spatial expression, but also in substrate specificity.

Transcriptional organization of a Drosophila glutamic acid decarboxylase gene

We previously described the sequence and expression pattern of a Drosophila mRMA (Gad) that encodes the major soluble form of glutamic acid decarboxylase (GAD). We now report the transcriptional organization of the Drosophila Gad gene. Based on a combination of DNA sequence, RNase protection, primer extension, and polymerase chain reaction analyses, we conclude that the transcription unit for a 3.1-kb Gad mRNA is composed of eight exons that span approximately 17-kb genomic interval. By this analysis, the site of Gad transcript initiation overlaps with a recognition sequence that confers binding of the zeste transcription factor to other promoter elements. We emphasize that our analysis of the Gad transcription unit provides no evidence for alternative RNA splicing as a mechanism for the generation of GAD isoforms. Thus, the several GAD-immunoreactive proteins (putative GAD isoforms) that can be detected in Drosophila extracts are probably encoded by distinct genes.

Drosophila GABAergic systems: sequence and expression of glutamic acid decarboxylase

A mammalian glutamic acid decarboxylase (GAD) cDNA probe has been utilized to isolate Drosophila cDNA clones that represent a genomic locus in chromosome region 64A. Deletion analysis indicates that this chromosomal locus encodes an enzymatically active GAD protein. The in vitro translation of cRNA representing a Drosophila cDNA clone yields a 57-kDa protein that can be immunoprecipitated by an anti-GAD antiserum. A GAD-immunoreactive protein of the same size can also be detected in Drosophila head extracts. The nucleotide sequence derived from two overlapping Drosophila cDNA clones predicts a 57,759-dalton protein composed of 510 residues that is 53% identical to mammalian GAD. Sequence comparisons of mammalian and Drosophila GAD identify two highly conserved regions (greater than or equal to 70% identity), one of which encompasses a putative co-factor-binding domain. Transcriptional analyses show that expression of the Drosophila Gad gene commences early in embryonic development (4-8 h) and continues in all later developmental stages. A 3.1-kb class of mRNA is detected throughout embryogenesis, in all three larval stages, in pupae, and in adults. This transcript class has a widespread distribution in the adult CNS. A smaller 2.6-kb transcript is expressed in a developmentally regulated manner; it is detected only in embryos and pupae.

A rapid purification of L-glutamic acid decarboxylase from the brain of the locust Schistocerca gregaria

L-Glutamic acid decarboxylase (GAD; EC 4.1.1.15) was purified to apparent homogeneity from the brain of the locust Schistocerca gregaria using a combination of chromatofocusing (Mono P) and gel filtration (Superose 12) media. The homogeneity of the enzyme preparation was established by native polyacrylamide gel electrophoresis (PAGE) with silver staining. The molecular weight of the purified enzyme was estimated from native gradient gel electrophoresis and gel filtration chromatography to be 97,000 +/- 4,000 and 93,000 +/- 5,000, respectively. When analysed by sodium dodecyl sulphate-PAGE, the enzyme was found to be composed of two distinct subunits of Mr 51,000 +/- 1,000 and 44,000 +/- 1,500. Tryptic peptide maps of iodinated preparations of these two subunits showed considerable homology, suggesting that the native enzyme is a dimer of closely related subunits. The purified enzyme had a pH optimum of 7.0-7.4 in 100 mM potassium phosphate buffer and an apparent Km for glutamate of 5.0 mM. The enzyme was strongly inhibited by the carbonyl-trapping reagent aminooxyacetic acid with an I50 value of 0.2 microM.

Assay and properties of glutamic acid decarboxylase in homogenates of crayfish nervous tissue

The activity of glutamic acid decarboxylase (GAD) was measured in homogenates of crayfish nervous tissue. Radioactive GABA and CO2 were formed from radioactive glutamic acid in approximately equimolar amounts. Product formation was linear for 9.5 hr at 11-32 degrees C with about 1-30 micrograms homogenate protein. Enzyme activity remained high at pH 7-10 but declined steeply above pH 10.5 and below pH 7. Enzyme activity was stimulated by pyridoxal phosphate, 2-mercaptoethanol, and potassium phosphate; at higher than optimal concentrations of each the activity was reduced. Sodium phosphate altered the stimulatory effect of potassium phosphate. Crayfish GAD behaves like a typical neural GAD but is distinguishable biochemically from GAD of other species.