Abstract
Carbohydrate-active enzymes are responsible for both the biosynthesis and breakdown of carbohydrates and glycoconjugates. They are involved in many metabolic pathways, in the biosynthesis and degradation of various biomolecules, such as bacterial exopolysaccharides, starch, cellulose, and lignin, and in the glycosylation of proteins and lipids. Their interesting reactions have attracted the attention of researchers belonging to different scientific fields ranging from basic research to biotechnology. Interest in carbohydrate-active enzymes is due not only to their ability to build and degrade biopolymers, which is highly relevant in biotechnology, but also because they are involved in bacterial biofilm formation, and in the glycosylation of proteins and lipids, which has important health implications. This Special Issue features a collection of research papers and reviews representing an up-to-date state of the art in this growing field of research to broaden our understanding about carbohydrate-active enzymes, their mutants, and their reaction products at the molecular level. Tindara Venuto et al. wrote a paper about alpha2,8-sialyltransferases from ray-finned fish and showed that, in tetrapods, duplicated st8sia genes like st8sia7, st8sia8, and st8sia9 have disappeared while orthologues are maintained in teleosts [1]. They reconstructed the evolutionary history of st8sia genes in fish genomes and by bioinformatics analysis showed changes in the conserved polysialyltransferase domain of the fish sequences possibly accounting for variable enzymatic activities [1]. PhNah20A, a β-N-acetylhexosaminidase from the marine bacterium Paraglaciecola hydrolytica S66T, was identified and characterized. By phylogenetic analysis, the authors discovered that PhNah20A is located outside clusters of other studied β-N-acetylhexosaminidases, in a unique position between bacterial and eukaryotic enzymes. PhNah20A is the first characterized member of a distinct subgroup within GH20 β-N-acetylhexosaminidases. The recombinant PhNah20A showed optimum hydrolytic activity on GlcNAc β-1,4 and β-1,3 linkages in chitobiose (GlcNAc)2 and GlcNAc-1,3-β-Gal-1,4-β-Glc (LNT2), the core structure of a human milk oligosaccharide, at pH 6.0 and 50 • C. Interestingly PhNah20A catalyzed the formation of LNT2, the non-reducing trisaccharide β-Gal-1,4-β-Glc-1,1-β-GlcNAc, and in low amounts the β-1,2-or β-1,3-linked trisaccharide β-Gal-1,4(β-GlcNAc)-1,x-Glc by a transglycosylation of lactose using 2-methyl-(1,2-dideoxy-α-d-glucopyrano)-oxazoline (NAG-oxazoline) as the donor [2]. The production of biofuels from lignocellulosic biomasses is hampered by the saccharification step of the biomasses requiring the concerted action of lignocellulose cellulases and hemicellulases. Zhang et al. characterized the secretome of Trichoderma harzianum EM0925 under induction of lignocellulose cellulases and hemicellulases [3]. Compared with the commercial enzyme preparations, the T. harzianum EM0925 enzyme cocktail presented significantly higher lignocellulolytic enzyme activities and hydrolysis efficiency against lignocellulosic biomasses. The enzyme mixture used on ultrafine grinding and alkali pretreated corn stover yielded 100% glucose and xylose. The authors suggest that natural cellulases mixed with the hemicellulases enzyme cocktail from T. harzianum Int.