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[摘要]：Two site-directed Mutations within the wild-type 2-O-benzoyltransferase (tbt) cDNA, from Taxus cuspidata plants, yielded air encoded protein containing replacement amino acids at Q19P and N23K that trial) to a solvent-exposed loop region. The likely significant changes in the biophysical properties invoked by these mutations Caused the overexpressed, modified TBT (mTBT) to partition into the Soluble enzyme fraction about 5-fold greater than the wild-type enzyme. Sufficient protein could now be acquired to examine the scope of the substrate specificity of mTBT by incubation with 7,13-O,O-diacetyl-2-O-debenzoylbaceatin III that was mixed individually with various substituted benzoyls, alkanoyls, and (E)-butenoyl CoA donors. The mTBT catalyzed the conversion of each 7,13-O,O-diacetyl-2-O-debenzoylbaccatin III to several 7,13-O,O-diacetyl-2-O-acyl-2-O-debenzoylbaccatin III analogues. The relative catalytic efficiency of mTBT with the 7,13-O,O-diacetyl-2-O-debenzoyl surrogate Substrate and heterole carbonyl CoA substrates was slightly greater than with the natural aroyl substrate benzoyl CoA, While substituted benzoyl CoA thioesters were less productive. Short-chain hydrocarbon carbonyl and cyclohexanoyl CoA thioesters were also productive, where C-4 Substrates were transferred by mTBT with similar to 10- to 17-fold greater catalytic efficiency compared to the transfer of benzoyl. The described broad specificity of mTBT suggests (flat a plethora of 2-O-acyl variants of the antimitotic paclitaxel can be assembled through biocatalytic sequences. |
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