Enzymes, biocatalysis and chemical biology

Chemical transformations that take advantage of biocatalysis are of great interest to chemists. The specific activity and selectivity of the enzymes allow them to perform different chemical reactions with high regio- and stereoselectivity, and a large number of biocatalyzed industrial processes have been already established. At the same time, we can observe the emergence of chemical biology, namely the scientific discipline spanning the fields of chemistry and biology and dealing with chemistry applied to biology. The aim of this Special Issue is to collect studies focused on biocatalysis applied to organic synthesis, as well as research related to chemical biology. The obtained contributions dealing with biotransformations, enzymology, the stereoselective synthesis of bioactive chemical compounds, active pharmaceutical ingredients, natural products and flavours have been collected in the present Issue. Overall, the Issue has gathered ten research articles. Two of these papers deal with fungal metabolism and fungi-mediated biotransformations. A first paper from Liu et al. [1]investigates themRNA and protein expressionlevels and the activities of?-glutamyl transpeptidase and L-cysteine sulfoxide lyase in correlation with the endogenous formaldehyde content in the edible mushroom Lentinula edodes at different growth stages. Formaldehyde is classified as a human carcinogen and can be found in natural and processed foods. Therefore, this research provided a molecular basis for understanding and controlling the endogenous formaldehyde formation in shiitake mushroom. A second paper from Serra and De Simeis [2] describes a study on the biotransformation of seven natural occurring apocarotenoids by means of eleven selected fungal species. The substrates, namely ionone (?-, ?- and ?-isomers), 3,4-dehydroionone, damascone (?- and ?-isomers) and theaspirane are relevant flavour and fragrances components. The observed transformations are mainly oxidation reactions that afford oxygenated products such as hydroxy- keto- or epoxy-derivatives. A very significant feature of the study concerns the prospective applicability of the fungi-mediated biotransformation of apocarotenoids for the synthesis of high value natural flavours. Since some ionone, damascone and theaspirane isomers are available in natural form and the biotransformation of a natural precursor is considered a "natural method" of synthesis, the flavours obtained by means of the fungi-mediated reactions possess natural status and could be commercialized accordingly. Four relevant works exploit the potential of some specific enzymes in biocatalyzed reactions. A first contribution from Wang et al. [3] reports on the glucosylation of ganoderic acid A, a bioactive triterpenoid isolated from the medicinal fungus Ganoderma lucidum. A new ganoderic acid A-26-O-?-glucoside was produced from the O-glucosylation with recombinant BsGT110, a glycosyltransferase isolated from Bacillus subtilis ATCC 6633. BsGT110 was the first glycosyltransferases identified as catalyzing the glycosylation of triterpenoid at the C-26 position. Since triterpenoid glycosides may improve the bioactivity of the triterpenoid aglycone, this study could be regarded as a new tool in natural product synthesis. The reduction of conjugated double bonds of citral using old yellow enzyme (OYE)-mediated biotransformation was studied by Ying et al. [4]. These researchers established that a significant increase of (R)-enantioselectivity in the (E/Z)-citral reduction was achieved by saturation mutagenesis of P76 Molecules 2020, 25, 2354; doi:10.3390/molecules25102354 www.mdpi.com/journal/molecules Molecules 2020, 25, 2354 2 of 3 and R330 in OYE2y. Remarkably, the variants P76M/R330H, P76G/R330H and P76S/R330H exhibited full (R)-enan