Cloning and Characterization of a Ginsenoside-Hydrolyzing α-L-Arabinofuranosidase, CaAraf51, From Cellulosimicrobium aquatile Lyp51

A Versatile β-Glycosidase from Petroclostridium xylanilyticum Prefers the Conversion of Ginsenoside Rb3 over Rb1, Rb2, and Rc to Rd by Its Specific Cleavage Activity toward 1,6-Glycosidic Linkages

To convert ginsenosides Rb1, Rb2, Rb3, and Rc into Rd by a single enzyme, a putative β-glycosidase (Pxbgl) from the xylan-degrading bacterium Petroclostridium xylanilyticum was identified and used. The kcat/Km value of Pxbgl for Rb3 was 18.18 ± 0.07 mM-1/s, which was significantly higher than those of Pxbgl for other ginsenosides. Pxbgl converted almost all Rb3 to Rd with a productivity of 5884 μM/h, which was 346-fold higher than that of only β-xylosidase from Thermoascus aurantiacus. The productivity of Rd from the Panax ginseng root and Panax notoginseng leaf was 146 and 995 μM/h, respectively. Mutants N293 K and I447L from site-directed mutagenesis based on bioinformatics analysis showed an increase in specific activity of 29 and 7% toward Rb3, respectively. This is the first report of a β-glycosidase that can simultaneously remove four different glycosyls at the C-20 position of natural PPD-type ginsenosides and produce Rd as the sole product from P. notoginseng leaf extracts with the highest productivity.

Purification and characterization of an α-l-arabinofuranosidase, α-l-AFase, for hydrolyzed ginsenoside Rc from Bacillus subtilis

Natural ginsenoside needs to be converted into rare ginsenoside before it can be readily absorbed into the bloodstream for action. In this study, an α-l-arabinofuranosidase (α-l-AFase) gene Bsafs2 was cloned from Bacillus subtilis (B. subtilis). Bsafs2 was ligated to the expression vector pET28a(+), and the expression vector was constructed and transformed into Escherichia coli (E. coli) BL21 heterologous recombinant expression to obtain α-l-AFase. α-l-AFase can hydrolyze at the C20 site of Ginsenoside Rc to obtain rare ginsenoside Rd. Studies on the enzymatic property showed that α-l-AFase had good tolerance to ethanol, glucose, and l-arabinose. The optimum temperature of α-l-AFase was 40 °C and pH = 5.5. Kinetic parameters Km of α-l-AFase for pNPαAraf and Ginsenoside Rc were 1.93 and 8.9 mmol/L, the Vmax were 26 and 154 μmol/min/mg, the Kcat were 24.14 and 1.48 S-1, respectively. This study provides the enzyme source for the biotransformation of Ginsenoside Rc.

Molecular cloning, expression, purification, and characterization of Bacillus subtilis hydrolyzed ginsenoside Rc of α-L-arabinofuranosidase in Escherichia coli

The α-L-arabinofuranosidase enzyme plays a crucial role in the degradation of ginsenosides. In this study, we successfully cloned and expressed a novel α-L-arabinofuranosidase bsafs gene (1503 bp, 501 amino acids, 55 kDa, and pI = 5.4) belonging to glycosyl hydrolase (GH) family 51 from Bacillus subtilis genome in Escherichia coli BL21 cells. The recombinant protein Bsafs was purified using Ni2+ sepharose fastflow affinity chromatography and exhibited a specific activity of 2.91 U/mg. Bsafs effectively hydrolyzed the α-L-arabinofuranoside at C20 site of ginsenoside Rc to produce Rd as the product. The Km values for hydrolysis of pNP-α-L-arabinofuranoside (pNPαAraf) and ginsenoside Rc were determined as 0.74 and 4.59 mmol/L, respectively; while the Vmax values for these substrates were found to be 24 and 164 μmol/min/mg, respectively; furthermore, the Kcat values for these enzymes were calculated as 22.3 and 1.58 S-1 correspondingly.

Microbial α-L-arabinofuranosidases: diversity, properties, and biotechnological applications

Arabinoxylans (AXs) are hemicellulosic polysaccharides consisting of a linear backbone of β-1,4-linked xylose residues branched by high content of α-L-arabinofuranosyl (Araf) residues along with other side-chain substituents, and are abundantly found in various agricultural crops especially cereals. The efficient bioconversion of AXs into monosaccharides, oligosaccharides and/or other chemicals depends on the synergism of main-chain enzymes and de-branching enzymes. Exo-α-L-arabinofuranosidases (ABFs) catalyze the hydrolysis of terminal non-reducing α-1,2-, α-1,3- or α-1,5- linked α-L-Araf residues from arabinose-substituted polysaccharides or oligosaccharides. ABFs are critically de-branching enzymes in bioconversion of agricultural biomass, and have received special attention due to their application potentials in biotechnological industries. In recent years, the researches on microbial ABFs have developed quickly in the aspects of the gene mining, properties of novel members, catalytic mechanisms, methodologies, and application technologies. In this review, we systematically summarize the latest advances in microbial ABFs, and discuss the future perspectives of the enzyme research.

Cloning, expression and characterization of a glycoside hydrolase family 51 α-l-arabinofuranosidase from Thermoanaerobacterium thermosaccharolyticum DSM 571

The present study focused on the characterization of a glycoside hydrolase 51 family α-l-arabinofuranosidase named TtAbf51 from thermophile Thermoanaerobacterium thermosaccharolyticum DSM 571. The recombinant TtAbf51 with 497 amino acids was successfully expressed in Escherichia coli BL21(DE3) and purified via nickel affinity chromatography, and native protein was a dimer verified by size exclusion chromatography. The TtAbf51 showed an optimum pH and temperature of 5.5 and 55 °C, and was relatively stable at pH 5.0-8.0 and up to 60 °C for 2 h of incubation. In addition, TtAbf51 was significantly inhibited by Cu²⁺, Zn²⁺ and 1 mM or 10 mM SDS. In the presence of 800 mM arabinose, the residual activity remained over 40% of the initial activity. In addition, the recombinant enzyme possessed a good catalytic effect for both synthesized and natural substrates, and the specific enzyme activity toward CM-linear arabinan reached 426.5 μmol min^-1 mg^-1. In summary, this study provides an α-l-arabinofuranosidase with potential in the synergistic hydrolysis of hemicellulose to fermentable sugars in applications such as liquid biofuels, food and beverages, and related industries.

Functional Characterization of a New Bifunctional Terpene Synthase LpNES1 from a Medicinal Plant Laggera pter odonta

Laggera pterodonta, known in China as 'Choulingdan' for its stimulous odor, has long been used as traditional herbal medicine. The essential oil of L. pterodonta, which exhibits various pharmacological activities, is a rich resource of monoterpenes and sesquiterpenes. To date, however, the terpene synthases responsible for their production remain unknown. In present study, a new terpene synthase gene (LpNES1) was identified from L. pterodonta, transcript level of which was significantly upregulated in response to methyl jasmonate treatment. Recombinant LpNES1 could synthesize (E)-nerolidol and minor β-farnesene from farnesyl diphosphate and linalool from geranyl diphosphate in vitro. Whereas, only sesquiterpenes including (E)-nerolidol and minor β-farnesene were released when LpNES1 was reconstituted in yeast, even coexpressed with a geranyl diphosphate synthase (ERG20^WW). Combined with subcellular localization experiment, the result indicated that the cytosol-targeted LpNES1 was responsible for (E)-nerolidol biosynthesis exclusively in L. pterodonta. Additionally, the expression level of LpNES1 gene was more prominent in floral buds than that in other tissues. LpNES1 characterized in present study not only lays the molecular foundation for sesquiterpene biosynthesis of L. pterodonta, but provides a key element for further biosynthesis of bioactive compound in microbes.

Two Key Amino Acids Variant of α-l-arabinofuranosidase from Bacillus subtilis Str. 168 with Altered Activity for Selective Conversion Ginsenoside Rc to Rd

α-l-arabinofuranosidase is a subfamily of glycosidases involved in the hydrolysis of l-arabinofuranosidic bonds, especially in those of the terminal non-reducing arabinofuranosyl residues of glycosides, from which efficient glycoside hydrolases can be screened for the transformation of ginsenosides. In this study, the ginsenoside Rc-hydrolyzing α-l-arabinofuranosidase gene, BsAbfA, was cloned from Bacilus subtilis, and its codons were optimized for efficient expression in E. coli BL21 (DE3). The recombinant protein BsAbfA fused with an N-terminal His-tag was overexpressed and purified, and then subjected to enzymatic characterization. Site-directed mutagenesis of BsAbfA was performed to verify the catalytic site, and the molecular mechanism of BsAbfA catalyzing ginsenoside Rc was analyzed by molecular docking, using the homology model of sequence alignment with other β-glycosidases. The results show that the purified BsAbfA had a specific activity of 32.6 U/mg. Under optimal conditions (pH 5, 40 °C), the kinetic parameters K_m of BsAbfA for pNP-α-Araf and ginsenoside Rc were 0.6 mM and 0.4 mM, while the K_cat/K_m were 181.5 s^-1 mM^-1 and 197.8 s^-1 mM^-1, respectively. More than 90% of ginsenoside Rc could be transformed by 12 U/mL purified BsAbfA at 40 °C and pH 5 in 24 h. The results of molecular docking and site-directed mutagenesis suggested that the E173 and E292 variants for BsAbfA are important in recognizing ginsenoside Rc effectively, and to make it enter the active pocket to hydrolyze the outer arabinofuranosyl moieties at C₂₀ position. These remarkable properties and the catalytic mechanism of BsAbfA provide a good alternative for the effective biotransformation of the major ginsenoside Rc into Rd.