The β-Fructofuranosidase from Rhodotorula dairenensis: Molecular Cloning, Heterologous Expression, and Evaluation of Its Transferase Activity

Insights into the transglucosylation activity of α-glucosidase from Schwanniomyces occidentalis

The α-glucosidase from Schwanniomyces occidentalis (GAM1p) was expressed in Komagataella phaffii to about 70 mg/L, and its transferase activity studied in detail. Several isomaltooligosaccharides (IMOS) were formed using 200 g/L maltose. The major production of IMOS (81.3 g/L) was obtained when 98% maltose was hydrolysed, of which 34.8 g/L corresponded to isomaltose, 26.9 g/L to isomaltotriose, and 19.6 g/L to panose. The addition of glucose shifted the IMOS synthesis towards products containing exclusively α(1 → 6)-linkages, increasing the production of isomaltose and isomaltotriose about 2-4 fold, enabling the formation of isomaltotetraose, and inhibiting that of panose to about 12 times. In addition, the potential of this enzyme to glycosylate 12 possible hydroxylated acceptors, including eight sugars and four phenolic compounds, was evaluated. Among them, only sucrose, xylose, and piceid (a monoglucosylated derivative of resveratrol) were glucosylated, and the main synthesised products were purified and characterised by MS and NMR. Theanderose, α(1 → 4)-D-glucosyl-xylose, and a mixture of piceid mono- and diglucoside were obtained with sucrose, xylose, and piceid as acceptors, respectively. Maximum production of theanderose reached 81.7 g/L and that of the glucosyl-xylose 26.5 g/L, whereas 3.4 g/L and only 1 g/L were produced of the piceid mono- and diglucoside respectively. KEY POINTS: • Overexpression of a yeast α-glucosidase producing novel molecules. • Yeast enzyme producing the heterooligosaccharides theanderose and glucosyl-xylose. • Glycosylation of the polyphenol piceid by a yeast α-glucosidase.

Insights into the Structure of the Highly Glycosylated Ffase from Rhodotorula dairenensis Enhance Its Biotechnological Potential

Rhodotorula dairenensis β-fructofuranosidase is a highly glycosylated enzyme with broad substrate specificity that catalyzes the synthesis of 6-kestose and a mixture of the three series of fructooligosaccharides (FOS), fructosylating a variety of carbohydrates and other molecules as alditols. We report here its three-dimensional structure, showing the expected bimodular arrangement and also a unique long elongation at its N-terminus containing extensive O-glycosylation sites that form a peculiar arrangement with a protruding loop within the dimer. This region is not required for activity but could provide a molecular tool to target the dimeric protein to its receptor cellular compartment in the yeast. A truncated inactivated form was used to obtain complexes with fructose, sucrose and raffinose, and a Bis-Tris molecule was trapped, mimicking a putative acceptor substrate. The crystal structure of the complexes reveals the major traits of the active site, with Asn387 controlling the substrate binding mode. Relevant residues were selected for mutagenesis, the variants being biochemically characterized through their hydrolytic and transfructosylating activity. All changes decrease the hydrolytic efficiency against sucrose, proving their key role in the activity. Moreover, some of the generated variants exhibit redesigned transfructosylating specificity, which may be used for biotechnological purposes to produce novel fructosyl-derivatives.

Tailoring fructooligosaccharides composition with engineered Zymomonas mobilis ZM4

Zymomonas mobilis ZM4 is an attractive host for the development of microbial cell factories to synthesize high-value compounds, including prebiotics. In this study, a straightforward process to produce fructooligosaccharides (FOS) from sucrose was established. To control the relative FOS composition, recombinant Z. mobilis strains secreting a native levansucrase (encoded by sacB) or a mutated β-fructofuranosidase (Ffase-Leu196) from Schwanniomyces occidentalis were constructed. Both strains were able to produce a FOS mixture with high concentration of 6-kestose. The best results were obtained with Z. mobilis ZM4 pB1-sacB that was able to produce 73.4 ± 1.6 g L^-1 of FOS, with a productivity of 1.53 ± 0.03 g L^-1 h^-1 and a yield of 0.31 ± 0.03 g_FOS g_sucrose^-1. This is the first report on the FOS production using a mutant Z. mobilis ZM4 strain in a one-step process. KEY POINTS: • Zymomonas mobilis was engineered to produce FOS in a one-step fermentation process. • Mutant strains produced FOS mixtures with high concentration of 6-kestose. • A new route to produce tailor-made FOS mixtures was presented.

Purification of Aspergillus tamarii mycelial fructosyltransferase (m-FTase), optimized FOS production, and evaluation of its anticancer potential

In the present study, generation of prebiotic fructooligosaccharides (FOS) using Aspergillus tamarii FTase was optimized by applying response surface methodology. Optimal FOS (251 g L^-1 ) was generated at 28.4°C, pH 7.0 and 50% (w/v) sucrose leading to 1.97-fold yield enhancement. The m-FTase was purified using ultrafiltration followed by HiTrap Q HP anion exchange chromatography resulting in 2.15-fold purified FTase with 12.76 U mg^-1 specific activity. Purified FTase (75 kDa) had K_m and V_max values of 1049.717 mM and 2.094 µmol min^-1  mg^-1 , respectively. FOS incorporation led to upregulation of caspase 3, caspase 9, and Bax genes suggesting mitochondrial apoptosis activation in cancer cells. The study describes characteristics of purified FTase from A. tamarii, production optimization of FOS and unravels the role of FOS in anticancer activity against HT-29 cells. PRACTICAL APPLICATION: This study provides detailed insights of kinetic and thermodynamic characteristics of purified FTase, a prebiotic FOS-generating enzyme. Moreover, the role of the apoptotic genes involved in anticancer activity, and the prebiotic potential of FOS is also investigated. These findings are important in the context of FOS applications, and the optimized production strategies make it useful for industrial application.