Enzymatic synthesis of polysaccharide-based copolymers

Abstract

The design of enzymatic routes for the production of biosourced copolymers represents an attractive alternative to chemical synthesis from fossil carbon. In this paper, we explore the potential of glycosynthesizing enzymes to produce novel block copolymers composed of various covalently-linked α-glucans with contrasting structures and physicochemical properties. To this end, various glucansucrases able to synthesize α-glucans with different types of α-osidic bonds from sucrose were tested for their ability to elongate oligosaccharide and polysaccharide acceptors with different structures from the native polymer synthesized by each enzyme. We showed that two enzymes -namely, the alternansucrase from Leuconostoc mesenteroides NRRL B-1355 (specific for α(1 → 6)/α(1 → 3)-linked alternan synthesis) and the dextransucrase DSR-MΔ1 from Leuconostoc citreum NRRL B-1299 (specific for α(1 → 6)-linked dextran formation) -were able to elongate α(1 → 4)-linked amylose and α(1 → 6)/α(1 → 3)-linked alternan respectively. Carrying out stepwise acceptor reactions, and after optimization of the acceptor size and donor/acceptor ratio, two types of diblock copolymers were synthesized -a dextran-b-alternan and an alternan-b-amylose -as well as the triblock copolymer dextran-b-alternan-b-amylose. Their structural characterization, performed by combining chromatographic, NMR and permethylation analyses, showed that the copolymer polymerization degree ranged from 29 to 170, which is the highest degree of polymerization ever reported for an enzymatically synthesized polysaccharide-based copolymer. The addition of dextran and alternan blocks to amylose resulted in conformational modifications and related flexibility changes, as demonstrated by small angle X-ray scattering.

Bacterial α-Glucan and Branching Sucrases from GH70 Family: Discovery, Structure–Function Relationship Studies and Engineering

“…These properties are exploited to produce functional oligosaccharides [ 28 ] in particular isomaltooligosaccharides [ 29 ], oligoalternans (oligosaccharides with alternating α-1,6 and α-1,3 linkages) [ 30 , 31 , 32 , 33 ], oligoreuterans with α-1,6 and α-1,4 linkages [ 34 ] or α-1,2 branched gluco oligosaccharides [ 35 , 36 , 37 , 38 , 39 ] commercialized under the brand name BioEcolans ® (Solabia) for food, healthcare or cosmetic applications. Furthermore, GSs and BRSs can also be used to produce glucoderivatives such as flavonoid glucosides [ 40 , 41 , 42 , 43 ] or glyco-co-polymers [ 44 , 45 ]. In family GH70, other types of polymerases have been recently discovered i.e., the 4,6 and 4,3-α-glucanotransferases [ 46 , 47 ].…”

Synthesis and Biopharmaceutical Applications of Sugar-Based Polymers: New Advances and Future Prospects

“…Two enzymes, alternansucrase and the dextransucrase DSR-MΔ1, were found to elongate amylose and alternan, respectively. 44 Therefore, diblock copolymers, i.e., a dextranb-alternan and an alternan-b-amylose, and a triblock copolymer, dextran-b-alternan-b-amylose, were synthesized. The highest DP enzymatically obtainable in the laboratory at present reached 170 for a glycan copolymer.…”

Extracellular polysaccharides produced by bacteria of the Leuconostoc genus

“…Alternan as low viscosity bulking agent and extender (Pilling and Frohberg 2009) can be used in a wide variety of foodstuffs (sauces, cream, yoghurt, jelly, ice cream, soups, baked products) in the form of powder or paste (0.1% w/w and above). The uses of alternan, including in food, have been mentioned and summarized in many reports and reviews (Gangoiti et al 2018;Giavasis 2013;Grimaud et al 2018;Harutoshi 2013;Park and Khan 2009;Patel et al 2012;Wangpaiboon et al 2018;Zannini et al 2015). It is mentioned that alternan could also replace polydextrose, maltodextrins and gum arabic for use as inks, glues, cosmetic creams and ointments (Côté 1992;Park and Khan 2009).…”