- Optimization of the kinetic resolution of the DL-phospho-monoesters of threonine and serine by random mutagenesis of the acid phosphatase from Salmonella enterica
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Acid phosphatases are enzymes with a broad substrate specificity showing hydrolytic activity towards several different organic phosphate monoesters, such as nucleotides and sugar phosphates. The acid phosphatase from Salmonella enterica ser. typhimurium LT2 (PhoN-Se) is able to hydrolyze O-phospho-DL-threonine to yield L-threonine with a very high enantioselectivity (E > 200). When O-phospho-DL-serine was hydrolyzed by PhoN-Se, D-serine was formed, however, the ee values rapidly dropped to 50 %. Random mutagenesis by error-prone PCR was performed on the phosphatase in order to increase its enantioselectivity in the formation of D-serine. Two variants with increased selectivity from a library of 9600 mutants have been found, N151D and V78L showing E values of 18.1 and 4.1, respectively, compared to 3.4 for the wild-type (WT) enzyme.
- Van Herk, Teunie,Hartog, Aloysius F.,Ruijssenaars, Harald J.,Kerkman, Richard,Schoemaker, Hans E.,Wever, Ron
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p. 1349 - 1352
(2008/09/16)
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- Enzymatic synthesis of β-hydroxy-α-amino acids based on recombinant D- and L-threonine aldolases
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To exploit the enzymatic method for the synthesis of β-hydroxy-α-amino acids, the genes coding for the Escherichia coli L-threonine aldolase (LTA; EC 2.1.2.1) and Xanthomonus oryzae D-threonine aldolase (DTA) were cloned and overexpressed in E. coli through primer-directed polymerase chain reactions. The purified recombinant enzymes were studied with respect to kinetics, specificity, stability, additive requirement, temperature profile, and pH dependency. DTA requires magnesium ion as a cofactor, while LTA needs no metal ions. These enzymes work well in the presence of DMSO with concentration up to 40%, and DMSO-induced rate acceleration of LTA-catalyzed reaction was observed. Both enzymes use pyridoxal phosphate coenzyme to activate glycine to react with a wide range of aldehydes. LTA gave erythro-β-hydroxy-α-L-amino acids with aliphatic aldehydes and the threo isomer with aromatic aldehydes as kinetically controlled products. On the other hand, DTA formed threo-β-hydroxy-α-D-amino acids as kinetically controlled products with aliphatic and aromatic aldehydes but the diastereoselectivity was lower than that of LTA. Under optimal conditions, several β-hydroxy-α-amino acid derivatives (3-hydroxyleucines, γ-benzyloxythreonines, γ-benzyloxymethylthreonines, and poplyoxamic acids) have been stereoselectively synthesized on preparative scales using these enzymes. Also, the tandem use of DTA and phosphatases has made possible the synthesis and separation of D-allo-threonine phosphate and D-threonine.
- Kimura, Teiji,Vassilev, Vassil P.,Shen, Gwo-Jenn,Wong, Chi-Huey
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p. 11734 - 11742
(2007/10/03)
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