We previously puri®ed a new esterase from the thermoacidophilic eubacterium Bacillus acidocaldarius whose N-terminal sequence corresponds to an open reading frame (ORF3) reported to show homology with the mammalian hormone-sensitive lipase (HSL)- like group of the esterase}lipase family. To compare the biochemical properties of this thermophilic enzyme with those of the homologous mesophilic and psychrophilic members of the HSL group, an overexpression system in Escherichia coli was established. The protein, expressed in soluble and active form at 10 mg}l E. coli culture, was puri®ed to homogeneity and characterized biochemically. The enzyme, a 34 kDa monomeric protein, was demonstrated to be a B§-type carboxylesterase (EC 3.1.1.1) on the basis of substrate speci®city and the action of inhibitors. Among the p-nitrophenyl (PNP) esters tested the best substrate was PNP-exanoate with Km and kcat values of 11³2 lM (mean³S.D., n¯3) and 6610³880 s−" (mean³S.D., n¯3)respectively at 70 °C and pH 7.1. In spite of relatively high sequence identity with the mammalian HSLs, the psychrophilic Moraxella TA144 lipase 2 and the human liver arylacetamide deacetylase, no lipase or amidase activity was detected. A series of substrates were tested for enantioselectivity. Substantial enantioselectivity was observed only in the resolution of (³)-3- bromo-5-(hydroxymethyl)-D#-isoxazoline, where the (R)-product was obtained with an 84% enantiomeric excess at 36% conversion. The enzyme was also able to synthesize acetyl esters when tested in vinyl acetate and toluene. Inactivation by diethylpyrocarbonate, diethyl-p-nitrophenyl phosphate, di-isopropylphospho ¯uoridate (DFP) and physostigmine, as well as labelling with [$H]DFP, supported our previous suggestion of a catalytic triad made up of Ser-His-Asp. The activity±stability± temperature relationship is discussed in relation to those of the homologous members of the HSL group.
Overexpression and properties of a new thermophilic and thermostable esterase from Bacillus acidocaldarius with sequence similarity to hormone-sensitive lipase subfamily
ADINOLFI, Elena;
1998
Abstract
We previously puri®ed a new esterase from the thermoacidophilic eubacterium Bacillus acidocaldarius whose N-terminal sequence corresponds to an open reading frame (ORF3) reported to show homology with the mammalian hormone-sensitive lipase (HSL)- like group of the esterase}lipase family. To compare the biochemical properties of this thermophilic enzyme with those of the homologous mesophilic and psychrophilic members of the HSL group, an overexpression system in Escherichia coli was established. The protein, expressed in soluble and active form at 10 mg}l E. coli culture, was puri®ed to homogeneity and characterized biochemically. The enzyme, a 34 kDa monomeric protein, was demonstrated to be a B§-type carboxylesterase (EC 3.1.1.1) on the basis of substrate speci®city and the action of inhibitors. Among the p-nitrophenyl (PNP) esters tested the best substrate was PNP-exanoate with Km and kcat values of 11³2 lM (mean³S.D., n¯3) and 6610³880 s−" (mean³S.D., n¯3)respectively at 70 °C and pH 7.1. In spite of relatively high sequence identity with the mammalian HSLs, the psychrophilic Moraxella TA144 lipase 2 and the human liver arylacetamide deacetylase, no lipase or amidase activity was detected. A series of substrates were tested for enantioselectivity. Substantial enantioselectivity was observed only in the resolution of (³)-3- bromo-5-(hydroxymethyl)-D#-isoxazoline, where the (R)-product was obtained with an 84% enantiomeric excess at 36% conversion. The enzyme was also able to synthesize acetyl esters when tested in vinyl acetate and toluene. Inactivation by diethylpyrocarbonate, diethyl-p-nitrophenyl phosphate, di-isopropylphospho ¯uoridate (DFP) and physostigmine, as well as labelling with [$H]DFP, supported our previous suggestion of a catalytic triad made up of Ser-His-Asp. The activity±stability± temperature relationship is discussed in relation to those of the homologous members of the HSL group.I documenti in SFERA sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
