L-(-)-threo-3-Hydroxyaspartic acid

One-Pot Production of L-threo-3-Hydroxyaspartic Acid Using Asparaginase-Deficient Escherichia coli Expressing Asparagine Hydroxylase of Streptomyces coelicolor A3(2).[Pubmed:25795668]

Appl Environ Microbiol. 2015 Jun;81(11):3648-54.

We developed a novel process for efficient synthesis of L-threo-3-hydroxyaspartic acid (L-THA) using microbial hydroxylase and hydrolase. A well-characterized mutant of asparagine hydroxylase (AsnO-D241N) and its homologous enzyme (SCO2693-D246N) were adaptable to the direct hydroxylation of L-aspartic acid; however, the yields were strictly low. Therefore, the highly stable and efficient wild-type asparagine hydroxylases AsnO and SCO2693 were employed to synthesize L-THA. By using these recombinant enzymes, L-THA was obtained by L-asparagine hydroxylation by AsnO followed by amide hydrolysis by asparaginase via 3-hydroxyasparagine. Subsequently, the two-step reaction was adapted to one-pot bioconversion in a test tube. L-THA was obtained in a small amount with a molar yield of 0.076% by using intact Escherichia coli expressing the asnO gene, and thus, two asparaginase-deficient mutants of E. coli were investigated. A remarkably increased L-THA yield of 8.2% was obtained with the asparaginase I-deficient mutant. When the expression level of the asnO gene was enhanced by using the T7 promoter in E. coli instead of the lac promoter, the L-THA yield was significantly increased to 92%. By using a combination of the E. coli asparaginase I-deficient mutant and the T7 expression system, a whole-cell reaction in a jar fermentor was conducted, and consequently, L-THA was successfully obtained from L-asparagine with a maximum yield of 96% in less time than with test tube-scale production. These results indicate that asparagine hydroxylation followed by hydrolysis would be applicable to the efficient production of L-THA.

(2S,3S,4R)-2-(carboxycyclopropyl)glycine, a potent and competitive inhibitor of both glial and neuronal uptake of glutamate.[Pubmed:7901789]

Neuropharmacology. 1993 Sep;32(9):833-7.

The effects of several diastereoisomers of L-2-(carboxycyclopropyl)glycine (CCG) on L-glutamate uptake were compared among three different preparations, glial plasmalemmal vesicles (GPV), synaptosomes and cultured astrocytes from rat hippocampus. The (2S,3S,4R)-isomer (L-CCG-III) inhibited a Na(+)-dependent high-affinity L-glutamate uptake in GPV and synaptosomes in a dose dependent manner at a micromolar range. The potency was quite similar to that of L-threo-beta-hydroxyaspartate in both subcellular fractions and much higher than L-aspartate-beta-hydroxamate, which were known as potent inhibitors of glutamate uptake. The (2S,3R,4S)-isomer (L-CCG-IV) also inhibited the glutamate uptake in GPV and synaptosomes, but it was about 100 times less active than L-CCG-III. The (2S,3S,4S)- and (2S,3R,4R)-isomers (L-CCG-I and L-CCG-II, respectively) hardly showed any inhibitory action on the glutamate uptake. Dixon plot analysis of the initial uptake rate revealed that the inhibition was in a competitive manner and the value of the inhibition constant (Ki) was about 1 microM in both GPV and synaptosomes. L-CCG-III effectively inhibited the glutamate uptake by cultured hippocampal astrocytes as well. These results suggested that L-CCG-III inhibited the glutamate uptake in both neurones and glial cells of the mammalian central nervous system in a similar manner.

Neurotoxicity of L-glutamate and DL-threo-3-hydroxyaspartate in the rat striatum.[Pubmed:2856883]

J Neurochem. 1985 Jan;44(1):247-54.

Destruction of the glutamatergic corticostriatal pathway potentiates the neurotoxic action of 1 mumol L-glutamate injected into the rat striatum, whereas the toxic effects of 10 nmol kainate are markedly attenuated. Injection of 170 nmol of the glutamate uptake inhibitor, DL-threo-3-hydroxyaspartate, into the intact striatum also causes neuronal degeneration, which is accompanied by a reduction in markers for cholinergic and GABAergic neurones. Prior removal of the corticostriatal pathway destroys the ability of DL-threo-3-hydroxyaspartate to cause lesions in the striatum. These results indicate that removal, or blockade, of uptake sites for glutamate increase the vulnerability of striatal neurones to the toxic effects of synaptically released glutamate.