Characterization of ergothionase from Burkholderia sp. HME13 and its application to enzymatic quantification of ergothioneine

Abstract

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: 19μM, V max: 270μmol/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.