Structural Comparison of a Promiscuous and a Highly Specific Sucrose 6F-Phosphate Phosphorylase

High-yield synthesis of 2-O-α-D-glucosyl-D-glycerate by a bifunctional glycoside phosphorylase

Osmolytes are produced by various microorganisms as a defense mechanism to protect cells and macromolecules from damage caused by external stresses in harsh environments. Due to their useful stabilizing properties, these molecules are applied as active ingredients in a wide range of cosmetics and healthcare products. The metabolic pathways and biocatalytic syntheses of glycosidic osmolytes such as 2-O-α-D-glucosyl-D-glycerate often involve the action of a glycoside phosphorylase. Here, we report the discovery of a glucosylglycerate phosphorylase from carbohydrate-active enzyme family GH13 that is also active on sucrose, which contrasts the strict specificity of known glucosylglycerate phosphorylases that can only use α-D-glucose 1-phosphate as glycosyl donor in transglycosylation reactions. The novel enzyme can be distinguished from other phosphorylases from the same family by the presence of an atypical conserved sequence motif at specificity-determining positions in the active site. The promiscuity of the sucrose-active glucosylglycerate phosphorylase can be exploited for the high-yielding and rapid synthesis of 2-O-α-D-glucosyl-D-glycerate from sucrose and D-glycerate. KEY POINTS: • A Xylanimonas protaetiae glycoside phosphorylase can use both d-glycerate and fructose as glucosyl acceptor with high catalytic efficiency • Biocatalytic synthesis of the osmolyte 2-O-α-d-glucosyl-d-glycerate • Positions in the active site of GH13 phosphorylases act as convenient specificity fingerprints.

Architecture, Function, Regulation, and Evolution of α-Glucans Metabolic Enzymes in Prokaryotes

Bacteria have acquired sophisticated mechanisms for assembling and disassembling polysaccharides of different chemistry. α-d-Glucose homopolysaccharides, so-called α-glucans, are the most widespread polymers in nature being key components of microorganisms. Glycogen functions as an intracellular energy storage while some bacteria also produce extracellular assorted α-glucans. The classical bacterial glycogen metabolic pathway comprises the action of ADP-glucose pyrophosphorylase and glycogen synthase, whereas extracellular α-glucans are mostly related to peripheral enzymes dependent on sucrose. An alternative pathway of glycogen biosynthesis, operating via a maltose 1-phosphate polymerizing enzyme, displays an essential wiring with the trehalose metabolism to interconvert disaccharides into polysaccharides. Furthermore, some bacteria show a connection of intracellular glycogen metabolism with the genesis of extracellular capsular α-glucans, revealing a relationship between the storage and structural function of these compounds. Altogether, the current picture shows that bacteria have evolved an intricate α-glucan metabolism that ultimately relies on the evolution of a specific enzymatic machinery. The structural landscape of these enzymes exposes a limited number of core catalytic folds handling many different chemical reactions. In this Review, we present a rationale to explain how the chemical diversity of α-glucans emerged from these systems, highlighting the underlying structural evolution of the enzymes driving α-glucan bacterial metabolism.

Enhancing regioselectivity of sucrose phosphorylase by loop engineering for glycosylation of L-ascorbic acid

Sucrose phosphorylase (SPase) has a remarkable capacity to synthesize numerous glucosides from abundantly available sucrose under mild conditions but suffers from specificity and regioselectivity issues. In this study, a loop engineering strategy was introduced to enhance the regioselectivity and substrate specificity of SPase for the efficient synthesis of 2-O-α-D-glucopyranosyl-L-ascorbic acid (AA-2G) via L-ascorbic acid (L-AA). P134, L341, and L343 were identified as "hotspots" for modulating the flexibility of loops, which significantly influenced the H-bonding network of L-AA in the active site, as well as the entrance of the substrate channel, thereby altering the regioselectivity and substrate specificity. Finally, the mutant L341V/L343F, with near-perfect control of the selectivity synthesis of the 2-OH group of L-AA (> 99%), was obtained. The AA-2G production by the mutant reached 244 g L^-1 in a whole-cell biotransformation system, and the conversion rate of L-AA reached 64%, which is the highest level reported to date. Our work also provides a successful loop engineering case for modulating the regioselectivity and specificity of sucrose phosphorylase. KEY POINTS: • "Hotspots" were identified in the flexible loops of sucrose phosphorylase. • Mutants exhibited improved regioselectivity and specificity against L-ascorbic acid. • Synthesized AA-2G with high yield and regioselectivity by whole-cell of mutant.

Discovery and Biotechnological Exploitation of Glycoside-Phosphorylases

Among carbohydrate active enzymes, glycoside phosphorylases (GPs) are valuable catalysts for white biotechnologies, due to their exquisite capacity to efficiently re-modulate oligo- and poly-saccharides, without the need for costly activated sugars as substrates. The reversibility of the phosphorolysis reaction, indeed, makes them attractive tools for glycodiversification. However, discovery of new GP functions is hindered by the difficulty in identifying them in sequence databases, and, rather, relies on extensive and tedious biochemical characterization studies. Nevertheless, recent advances in automated tools have led to major improvements in GP mining, activity predictions, and functional screening. Implementation of GPs into innovative in vitro and in cellulo bioproduction strategies has also made substantial advances. Herein, we propose to discuss the latest developments in the strategies employed to efficiently discover GPs and make the best use of their exceptional catalytic properties for glycoside bioproduction.

Development of thermostable sucrose phosphorylase by semi-rational design for efficient biosynthesis of alpha-D-glucosylglycerol

Abstract

Sucrose phosphorylase (SPase) can specifically catalyze transglycosylation reactions and can be used to enzymatically synthesize α-D-glycosides. However, the low thermostability of SPase has been a bottleneck for its industrial application. In this study, a SPase gene from Leuconostoc mesenteroides ATCC 12,291 (LmSPase) was synthesized with optimized codons and overexpressed successfully in Escherichia coli. A semi-rational design strategy that combined the FireProt (a web server designing thermostable proteins), structure–function analysis, and molecular dynamic simulations was used to improve the thermostability of LmSPase. Finally, one single-point mutation T219L and a combination mutation I31F/T219L/T263L/S360A (Mut4) with improved thermostability were obtained. The half-lives at 50 °C of T219L and Mut4 both increased approximately two-fold compared to that of wild-type LmSPase (WT). Furthermore, the two variants T219L and Mut4 were used to produce α-D-glucosylglycerol (αGG) from sucrose and glycerol by incubating with 40 U/mL crude extracts at 37 °C for 60 h and achieved the product concentration of 193.2 ± 12.9 g/L and 195.8 ± 13.1 g/L, respectively, which were approximately 1.3-fold higher than that of WT (150.4 ± 10.0 g/L). This study provides an effective strategy for improving the thermostability of an industrial enzyme.

Key points

• Predicted potential hotspot residues directing the thermostability of LmSPase by semi-rational design

• Screened two positive variants with higher thermostability and higher activity

• Synthesized α-D-glucosylglycerol to a high level by two screened positive variants

Supplementary Information

The online version contains supplementary material available at 10.1007/s00253-021-11551-0.

Sucrose Phosphorylase and Related Enzymes in Glycoside Hydrolase Family 13: Discovery, Application and Engineering

Sucrose phosphorylases are carbohydrate-active enzymes with outstanding potential for the biocatalytic conversion of common table sugar into products with attractive properties. They belong to the glycoside hydrolase family GH13, where they are found in subfamily 18. In bacteria, these enzymes catalyse the phosphorolysis of sucrose to yield α-glucose 1-phosphate and fructose. However, sucrose phosphorylases can also be applied as versatile transglucosylases for the synthesis of valuable glycosides and sugars because their broad promiscuity allows them to transfer the glucosyl group of sucrose to a diverse collection of compounds other than phosphate. Numerous process and enzyme engineering studies have expanded the range of possible applications of sucrose phosphorylases ever further. Moreover, it has recently been discovered that family GH13 also contains a few novel phosphorylases that are specialised in the phosphorolysis of sucrose 6F-phosphate, glucosylglycerol or glucosylglycerate. In this review, we provide an overview of the progress that has been made in our understanding and exploitation of sucrose phosphorylases and related enzymes over the past ten years.