title: 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.
abstract: 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.
authors.affiliation: MSD Animal Health Innovation GmbH, Zur Propstei, 55270 Schwabenheim, Germany. thomas.ilg@msd.de
authors.forename: Thomas
authors.initials: T
authors.lastname: Ilg
authors.forename: Michael
authors.initials: M
authors.lastname: Berger
authors.forename: Sandra
authors.initials: S
authors.lastname: Noack
authors.forename: Andreas
authors.initials: A
authors.lastname: Rohwer
authors.forename: Michael
authors.initials: M
authors.lastname: Gaßel
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D003001:Cloning, Molecular; D058251:Ctenocephalides / Q000737:chemistry / Q000201:enzymology* / Q000235:genetics / Q000254:growth & development; D004331:Drosophila melanogaster / Q000737:chemistry / Q000201:enzymology* / Q000235:genetics / Q000254:growth & development; D004353:Drug Evaluation, Preclinical; D004791:Enzyme Inhibitors / Q000494:pharmacology*; D018507:Gene Expression Regulation, Developmental; D005968:Glutamate Decarboxylase / Q000037:antagonists & inhibitors / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism; D057166:High-Throughput Screening Assays; D019476:Insect Proteins / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism; D051379:Mice; D008969:Molecular Sequence Data; D010802:Phylogeny; D048494:Rhipicephalus / Q000737:chemistry / Q000201:enzymology* / Q000235:genetics / Q000254:growth & development; D016415:Sequence Alignment
chemical_list: D004791:Enzyme Inhibitors; D019476:Insect Proteins; D005968:Glutamate Decarboxylase; C402565:glutamate decarboxylase 1