Purification of an amide hydrolase DamH from Delftia sp. T3-6 and its gene cloning, expression, and biochemical characterization

摘要

A highly active amide hydrolase (DamH) was purified from Delftia sp. T3-6 using ammonium sulfate precipitation, diethylaminoethyl anion exchange, hydrophobic interaction chromatography, and Sephadex G-200 gel filtration. The molecular mass of the purified enzyme was estimated to be 32 kDa by sodium dodecyl sulfate (SDS)–polyacrylamide gel electrophoresis. The sequence of the N-terminal 15 amino acid residues was determined to be Gly-Thr-Ser-Pro-Gln-Ser-Asp-Phe-Leu-Arg-Ala-Leu-Phe-Gln-Ser. Based on the Nterminal sequence and results of peptide mass fingerprints, the gene (damH) was cloned by PCR amplification and expressed in Escherichia coli BL21(DE3). DamH was a bifunctional hydrolase showing activity to amide and ester bonds. The specific activities of recombinant DamH were 5,036 U/mg for 2′-methyl-6′-ethyl-2-chloroacetanilide (CMEPA) (amide hydrolase function) and 612 U/mg for 4-nitrophenyl acetate (esterase function). The optimumsubstrate of DamH was CMEPA, with K_m and k_(cat) values of 0.197 mM and 2,804.32 s~(-1), respectively. DamH could also hydrolyze esters such as 4-nitrophenyl acetate, glycerol tributyrate, and caprolactone. The optimal pH and temperature for recombinant DamH were 6.5 and 35 °C, respectively; the enzyme was activated by Mn~(2+) and inhibited by Cu~(2+), Zn~(2+), Ni~(2+), and Fe~(2+). DamH was inhibited strongly by phenylmethylsulfonyl and SDS and weakly by ethylenediaminetetraacetic acid and dimethyl sulfoxide.