A Pseudomonas putida ATCC12633 gene, dpkA, encoding a putative protein annotated as malate/L-lactate dehydrogenase in various sequence data bases was disrupted by homologous recombination. The resultant dpkA ؊ mutant was deprived of the ability to use D-lysine and also D-proline as a sole carbon source. The dpkA gene was cloned and overexpressed in Escherichia coli, and the gene product was characterized. The enzyme showed neither malate dehydrogenase nor lactate dehydrogenase activity but catalyzed the NADPH-dependent reduction of such cyclic imines as ⌬ 1 -piperideine-2-carboxylate and ⌬ 1 -pyrroline-2-carboxylate to form L-pipecolate and L-proline, respectively. NADH also served as a hydrogen donor for both substrates, although the reaction rates were less than 1% of those with NADPH. The reverse reactions were also catalyzed by the enzyme but at much lower rates. Thus, the enzyme has dual metabolic functions, and we named the enzyme ⌬ 1 -piperideine-2-carboxylate/⌬ 1 -pyrroline-2-carboxylate reductase, the first member of a novel subclass in a large family of NAD(P)-dependent oxidoreductases.Lactate dehydrogenase (LDH) 1 and malate dehydrogenase (MDH) comprise a complex protein superfamily with multiple enzyme homologs found in eubacteria, Archaea, and eukaryotes (1). They catalyze NAD(P)-dependent interconversions between lactate and pyruvate and between malate and oxaloacetate, respectively. However, a new class of NAD(P)-dependent malate/L-lactate dehydrogenases with no sequence homology to "orthodox" MDH or LDH has been demonstrated (2, 3). Moreover, they have no Rossmann fold, which is a sixstranded parallel -sheet core surrounded on both sides by helices (4), in their NAD(P)-binding domains in contrast to the orthodox proteins. Consequently, the new class of malate/Llactate dehydrogenase family has been distinguished from the orthodox one as shown in protein data bases such as InterPro (www.ebi.ac.uk/interpro/index.html) (5) and Pfam (www.sanger. ac.uk/Software/Pfam/) (6). However, many of the family members are annotated without functional evidence as MDH or LDH only because of their sequence similarities to those of a few enzymes such as MDH from Methanothermus fervidus (2) and LDH from Alcaligenes eutrophus (3). In fact, three hypothetical MDHs of this family have been shown to be (S)-2-hydroxyacid dehydrogenase (7), ureidoglycolate dehydrogenase (8), and 2,3-diketo-L-gulonate reductase (9). The NAD(P) dependence is common to them, but no other functional similarities can be assigned among them. Thus, we expect the occurrence of various other proteins with new functions in this family even though they are annotated as MDH (or LDH) in protein data bases.Pseudomonas strains use both enantiomers of lysine as a sole source of carbon (as well as nitrogen) (10, 11). L-Lysine is catabolized by Pseudomonas putida through the ␦-aminovalerate pathway (11), whereas D-lysine is catabolized through the pipecolate pathway involving a series of reactions through six-carbon cyclic intermediates (12, 13) (Fig. 1)...
We identified ergothionase, which catalyzes conversion of ergothioneine to thiolurocanic acid and trimethylamine, in a newly isolated ergothioneine-utilizing strain, Burkholderia sp. HME13. The enzyme was purified and its N-terminal amino acid sequence was determined. Based on the amino acid sequence, the gene encoding the enzyme was cloned and expressed in Escherichia coli. The recombinant enzyme was purified to homogeneity and characterized. The enzyme consisted of four identical 55-kDa subunits. The enzyme showed maximum activity at pH 8.0 and 65 °C and was stable between pH 7.0 and pH 10.0 and up to 60 °C. The enzyme acted on ergothioneine (K m: 19 μM, V max: 270 μmol/min/mg), but not D-histidine, L-histidine, D-tyrosine, L-tyrosine, D-phenylalanine, or L-phenylalanine. The enzyme was activated by BaCl2 and strongly inhibited by CuSO4, ZnSO4, and HgCl2. The amino acid sequence of ergothionase showed 23 % similarity to histidine ammonia-lyase (HAL) from Pseudomonas putida and 17 % similarity to phenylalanine ammonia-lyase (PAL) from parsley. However, the tripeptide sequence, Ala-Ser-Gly, which is important for catalysis in both HAL and PAL, was not conserved in ergothionase. The application of ergothionase for the quantification of ergothioneine contained in practical food and blood samples was investigated by performing a recovery test. Satisfactory recovery data (98.7-104 %) were obtained when ergothioneine was added to extract of tamogitake and hemolysis blood.
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