Abstract
For the efficient biotransformation of cucurbitacin B 2-o-β-d-glucoside (CuBg) to cucurbitacin B (CuB) in Cucumis melo pedicel extracts, the β-glucosidase gene bglS—consisting of 1344 bp (447 amino acids) from Streptomyces sp. RW-2—was cloned and expressed in Escherichia coli BL21(DE3). The activity of recombinant β-glucosidase with p-nitrophenyl-β-d-glucoside (pNPG) as a substrate was 3.48 U/mL in a culture. Using the recombinant β-glucosidase for the biotransformation of C. melo pedicel extracts, CuBg was converted into CuB with a conversion rate of 87.6% when the concentration of CuBg was 0.973 g/L in a reaction mixtures. The concentration of CuB in C. melo pedicel extracts was improved from 13.6 to 20.2 g/L after biotransformation. The present study provides high-efficiency technology for the production of CuB from its glycoside by biotransformation.
Highlights
Cucurbitacin B (CuB) has been reported to show various biological activities, such as anti-inflammatory, anticancer, antimicrobial, antidiabetic, antiobesity, and antihyperglycemic effects [1,2,3,4,5]
When C. melo pedicel extracts were used as the substrate, cucurbitacin B 2-O-β-D-glucoside (CuBg) was converted into CuB with an almost 100% conversion rate, and the concentration of CuB in C. melo pedicel extracts doubled after biotransformation
RW-2, and a sequence of approximately 1400 bp was obtained by polymerase chain reaction (PCR)
Summary
Cucurbitacin B (CuB) has been reported to show various biological activities, such as anti-inflammatory, anticancer, antimicrobial, antidiabetic, antiobesity, and antihyperglycemic effects [1,2,3,4,5]. Though CuB is not used worldwide as a drug at present, it has been considered to be the main active ingredient in extracts of Cucumis melo L. pedicel, which have been used as a traditional herbal medicine (HuLuSu Pian) for the digestive system and hepatic diseases for more than 20 years in China [7]. Our analysis showed that the contents of CuB and CuBg in C. melo pedicels from Bozhou (Anhui, China) were 13.6 and 9.73 mg/g, respectively. Due to the relatively low bioavailability of glycosides [10], CuBg is not considered to be an active ingredient in extracts of C. melo pedicel. When extracts from C. melo pedicels were treated by 0.1 mol/L acetic acid, the content of CuB was only increased by 7.46% [11]. Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations
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