The plasmid vectors, pBS2ndd and pBS3ndd, for versatile cloning with low background in Escherichia coli

Expression and characterization of a recombinant stevioside hydrolyzing β-glycosidase from Enterococcus casseliflavus

The demand for steviol glycosides, non-caloric sweet components of Stevia rebaudiana Bertoni (stevia) leaves, has increased considerably as a benefit to enhance human health. However, the supply has remained challenging due to limited production, with the lack of a specific steviol glycoside hydrolyzing enzyme. In this study, a novel β-glucosidase (EcBgl) from Enterococcus casseliflavus was cloned and expressed in Escherichia coli. An EcBgl consists of 721 amino acids corresponding to a molecular mass of 79.37 kDa. The EcBgl was purified to homogeneity, followed by enzyme characterization. The enzyme showed optimum pH and temperature at 6.0 and 37 °C, and exhibited the kinetic constants k_cat/K_m for pNPG and k_cat/K_m for stevioside of 8583 mM^-1s^-1 and 95.41 mM^-1s^-1, respectively. When compared to the stevioside hydrolyzing β-glycosidases previously reported, EcBgl was found to be the most efficient enzyme. EcBgl also rendered hydrolysis of the stevioside to produce rubusoside, a rare steviol glycoside with a pharmaceutical solubilizing property, by cleaving at the glucose moiety. In addition, the enzyme demonstrated substantial resistance against amygdalin, so it served as a potential enzyme in agricultural and pharmaceutical applications.

A novel series of high-efficiency vectors for TA cloning and blunt-end cloning of PCR products

An efficient PCR cloning method is indispensable in modern molecular biology, as it can greatly improve the efficiency of DNA cloning processes. Here, I describe the development of three vectors for TA cloning and blunt-end cloning. Specifically, pCRT and pCRZeroT were designed to improve the efficiency of TA cloning. pCRZeroT can also be used with pCRZero to facilitate blunt-end cloning using the ccdB gene. Using pCRZero and pCRZeroT and applying the Golden Gate reaction, I developed a direct PCR cloning protocol with non-digested circular vectors and PCR products. This direct PCR cloning protocol yielded colony-formation rates and cloning efficiencies that are comparable with those obtained by conventional PCR cloning with pre-digested vectors and PCR products. The three plasmids I designed are available from Addgene (https://www.addgene.org/).