Restriction enzymes, DNA polymerases, T4 DNA ligases and a site-directed mutagenesis kit were purchased from Takara (Dalian, China) and Vazyme (Nanjing, China). DNA purification kits, gel extraction kits, BCA-protein quantification assay kits, and plasmid extraction kits were purchased from Biomega (Shanghai, China). Protein marker (MM1397-500) was purchased from GenScript (Nanjing, China). ArEH gene synthesis was completed by Qinglan (Wuxi, China) and DNA sequencingwas performed by GENEWIZ (Suzhou, China). DNA manipulations including PCR, agarose gel electrophoresis, restriction enzyme digestion, ligation and transformation were performed following standard procedures from the manufacturers’ protocols.
Epoxide hydrolases (EHs) are attractive enzymes for producing enantiopure epoxides and diols, but do not display enough stability when lysates or Escherichia coli whole cells are used as biocatalysts. In this work, an organic-solvent tolerant strain Rhodococcus ruber THdAdN was utilized to overexpress an epoxide hydrolase from Agrobacterium radiobacter (ArEH), using E. coli BL21(DE3) as a control. The proportion of ArEH in all soluble proteins of R. ruber THdAdN(ArEH) reached 30.3%, which was comparable to that of E. coli BL21(DE3)(ArEH). Due to a higher cell density in flask cultivation, the maximum ArEH activity of R. ruber THdAdN(ArEH) toward epichlorohydrin (ECH) reached 5.4 U/mL, approximatel... More
Epoxide hydrolases (EHs) are attractive enzymes for producing enantiopure epoxides and diols, but do not display enough stability when lysates or Escherichia coli whole cells are used as biocatalysts. In this work, an organic-solvent tolerant strain Rhodococcus ruber THdAdN was utilized to overexpress an epoxide hydrolase from Agrobacterium radiobacter (ArEH), using E. coli BL21(DE3) as a control. The proportion of ArEH in all soluble proteins of R. ruber THdAdN(ArEH) reached 30.3%, which was comparable to that of E. coli BL21(DE3)(ArEH). Due to a higher cell density in flask cultivation, the maximum ArEH activity of R. ruber THdAdN(ArEH) toward epichlorohydrin (ECH) reached 5.4 U/mL, approximately 5-fold higher than that of E. coli BL21(DE3)(ArEH). More importantly, compared with E. coli BL21(DE3)(ArEH), ArEH in R. ruber THdAdN(ArEH) showed a 10-fold enhanced thermostability, better tolerance against alkali pH, and reduced substrate and product inhibition, which significantly improved its performance in the resolution of high concentration ECH. By substrate feeding, 98.5% ee (R)-ECH was obtained with a 35.5% yield from 512 mM racemic ECH hydrolyzed by R. ruberTHdAdN(ArEH). Compared with using free enzyme as biocatalysts, utilization of the R. ruber cells harboring ArEH improved the final (R)-ECH concentration by 46%.
关键词
Rhodococcus ruberWhole-cell biocatalystsEpoxide hydrolaseStability and organic-solvent toleranceChiral epoxides