Unravelling Regioselectivity of Leuconostoc citreum ABK-1 Alternansucrase by Acceptor Site Engineering

Alternansucrase (ALT, EC 2.4.1.140) is a glucansucrase that can generate α-(1,3/1,6)-linked glucan from sucrose. Previously, the crystal structure of the first alternansucrase from Leuconostoc citreum NRRL B-1355 was successfully elucidated; it showed that alternansucrase might have two acceptor subsites (W675 and W543) responsible for the formation of alternating linked glucan. This work aimed to investigate the primary acceptor subsite (W675) by saturated mutagenesis using Leuconostoc citreum ABK-1 alternansucrase (LcALT). The substitution of other residues led to loss of overall activity, and formation of an alternan polymer with a nanoglucan was maintained when W675 was replaced with other aromatic residues. Conversely, substitution by nonaromatic residues led to the synthesis of oligosaccharides. Mutations at W675 could potentially cause LcALT to lose control of the acceptor molecule binding via maltose–acceptor reaction—as demonstrated by results from molecular dynamics simulations of the W675A variant. The formation of α-(1,2), α-(1,3), α-(1,4), and α-(1,6) linkages were detected from products of the W675A mutant. In contrast, the wild-type enzyme strictly synthesized α-(1,6) linkage on the maltose acceptor. This study examined the importance of W675 for transglycosylation, processivity, and regioselectivity of glucansucrases. Engineering glucansucrase active sites is one of the essential approaches to green tools for carbohydrate modification.

Preservation of the donor–acceptor character of a carbazole–phenalenone dyad upon adsorption on Pt(111)

The donor–acceptor character of a donor–bridge–acceptor molecule is traced along the complexation with a Pt adatom and adsorption on a Pt(111) substrate. The non-planarity enables the partial preservation of the donor–acceptor character.

Molecular Conformation Modulating Luminescence Switching between Delayed Fluorescence and Room-Temperature Phosphorescence

A new pure organic donor-acceptor molecule, (4-chlorophenyl)(5H-dibenzo[b,f]azepin-5-yl)methanone (IS-CBZ) was designed and synthesized, which demonstrates near ultraviolet (NUV) delayed fluorescence (DF) and dual emission of NUV DF and yellow room-temperature phosphorescence...

Applications of Oxidoreductases

Oxidoreductases comprise of a large group of enzymes catalyzing the transfer of electrons from an electron donor to an electron acceptor molecule, commonly taking nicotinamide adenine dinucleotide phosphate (NADP) or nicotinamide adenine dinucleotide (NAD) as cofactors. Research on the potential applications of oxidoreductases on the growth of oxidoreductase-based diagnostic tests and better biosensors, in the design of inventive systems for crucial coenzymes regeneration, and in the creation of oxidoreductase-based approaches for synthesis of polymers and oxyfunctionalized organic substrates have made great progress. This chapter focuses on biocatalytic applications of oxidoreductases, since many chemical and biochemical transformations involve oxidation/reduction processes, developing practical applications of oxidoreductases has long been a significant target in biotechnology. Oxidoreductases are appropriate catalysts owing to their biodegradability, specificity and efficiency and may be employed as improved biocatalysts to substitute the toxic/expensive chemicals, save on energy/resources consumption, generate novel functionalities, or reduce complicated impacts on environment.