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Synthesis and evaluation of novel aromatic substrates and competitive inhibitors of GABA aminotransferase.

ABSTRACT: The design, synthesis, and evaluation of novel gamma-aminobutyric acid aminotransferase (GABA-AT) inhibitors and inactivators can lead to the discovery of new GABA-related therapeutics. To this end, a series of aromatic amino acid compounds was synthesized to aid in the design of new inhibitors and inactivators of GABA-AT. All compounds were tested as competitive inhibitors of GABA-AT. The amino acids with benzylic amines were also tested as substrates for GABA-AT. It was found that these compounds were all poor competitive inhibitors of GABA-AT, but some were substrates of the enzyme, suggesting their utility as scaffolds for potential GABA-AT mechanism-based inactivators. Computer modeling was used to rationalize the substrate activity of the various compounds.

SUBMITTER: Clift MD

PROVIDER: S-EPMC2480492 | biostudies-literature | 2008 May

REPOSITORIES: biostudies-literature

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Synthesis and evaluation of novel aromatic substrates and competitive inhibitors of GABA aminotransferase.

Clift Michael D MD Silverman Richard B RB

Bioorganic & medicinal chemistry letters 20071022 10

The design, synthesis, and evaluation of novel gamma-aminobutyric acid aminotransferase (GABA-AT) inhibitors and inactivators can lead to the discovery of new GABA-related therapeutics. To this end, a series of aromatic amino acid compounds was synthesized to aid in the design of new inhibitors and inactivators of GABA-AT. All compounds were tested as competitive inhibitors of GABA-AT. The amino acids with benzylic amines were also tested as substrates for GABA-AT. It was found that these compou ...[more]

PMID: 17988865

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Project description:Pseudomonas putida is a highly solvent-resistant microorganism and useful chassis for the production of value-added compounds from lignocellulosic residues, in particular aromatic compounds that are made from phenylalanine. The use of these agricultural residues requires a two-step treatment to release the components of the polysaccharides of cellulose and hemicellulose as monomeric sugars, the most abundant monomers being glucose and xylose. Pan-genomic studies have shown that Pseudomonas putida metabolizes glucose through three convergent pathways to yield 6-phosphogluconate and subsequently metabolizes it through the Entner-Doudoroff pathway, but the strains do not degrade xylose. The valorization of both sugars is critical from the point of view of economic viability of the process. For this reason, a P. putida strain was endowed with the ability to metabolize xylose via the xylose isomerase pathway, by incorporating heterologous catabolic genes that convert this C5 sugar into intermediates of the pentose phosphate cycle. In addition, the open reading frame T1E_2822, encoding glucose dehydrogenase, was knocked-out to avoid the production of the dead-end product xylonate. We generated a set of DOT-T1E-derived strains that metabolized glucose and xylose simultaneously in culture medium and that reached high cell density with generation times of around 100 min with glucose and around 300 min with xylose. The strains grew in 2G hydrolysates from diluted acid and steam explosion pretreated corn stover and sugarcane straw. During growth, the strains metabolized > 98% of glucose, > 96% xylose and > 85% acetic acid. In 2G hydrolysates P. putida 5PL, a DOT-T1E derivative strain that carries up to five independent mutations to avoid phenylalanine metabolism, accumulated this amino acid in the medium. We constructed P. putida 5PLΔgcd (xylABE) that produced up to 250 mg l-1 of phenylalanine when grown in 2G pretreated corn stover or sugarcane straw. These results support as a proof of concept the potential of P. putida as a chassis for 2G processes.

Project description:Gamma-aminobutyric acid aminotransferase (GABA-AT), a pyridoxal 5'-phosphate dependent enzyme, catalyzes the degradation of the inhibitory neurotransmitter gamma-aminobutyric acid (GABA) to succinic semialdehyde with concomitant conversion of pyridoxal 5'-phosphate (PLP) to pyridoxamine 5'-phosphate (PMP). The enzyme then catalyzes the conversion of alpha-ketoglutarate to the excitatory neurotransmitter L-glutamate. Racemic 4-amino-3-fluorobutanoic acid (3-F-GABA) was shown previously to act as a substrate for GABA-AT, not for transamination, but for HF elimination. Here we report studies of the reaction catalyzed by GABA-AT on (R)- and (S)-3-F-GABA. Neither enantiomer is a substrate for transamination. Very little elimination from the (S)-enantiomer was detected using a coupled enzyme assay; The rate of elimination of HF from the (R)-enantiomer is at least 10 times greater than that for the (S)-enantiomer. The (R)-enantiomer is about 20 times more efficient as a substrate for GABA-AT catalyzed HF elimination than GABA is a substrate for transamination. The (R)-enantiomer also inhibits the transamination of GABA 10 times more effectively than the (S)-enantiomer. Using a combination of computer modeling and the knowledge that vicinal C-F and C-NH3+ bonds have a strong preference to align gauche rather than anti to each other, it is concluded that on binding of free 3-F-GABA to GABA-AT the optimal conformation places the C-NH3+ and C-F bonds gauche in the (R)-enantiomer but anti in the (S)-enantiomer. Furthermore, the dynamic binding process and the bioactive conformation of GABA bound to GABA-AT have been inferred on the basis of the different biological behavior of the two enantiomers of 3-F-GABA when they bind to the enzyme. The present study suggests that the C-F bond can be utilized as a conformational probe to explore the dynamic binding process and provide insight into the bioactive conformation of substrates, which cannot be easily determined by other biophysical approaches.

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Synthesis and evaluation of novel aromatic substrates and competitive inhibitors of GABA aminotransferase.

Publications

Synthesis and evaluation of novel aromatic substrates and competitive inhibitors of GABA aminotransferase.

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