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The β-glucosidases (β-D-glucoside glucohydrolase, EC 3.2.1.21) hydrolyze glycosidic bonds of alkyl-, amino-, or aryl-β-D-glucosides, cyanogenic glucosides, disaccharides and short oligosaccharides and can also catalyze the synthesis of glycosyl-bonds between different molecules via transglycosylation. Due to their ubiquitous phylogenetic distribution, substrate diversity and ability to both hydrolyze and synthesize glycosidic bonds, the catalysis and regulation of β-glucosidases have been extensively studied. Many β-glucosidases are inhibited by the reaction product glucose, and reduced catalytic activity may limit the biotechnological and industrial applications of these enzymes and this has stimulated the search for β-glucosidases that maintain their activity at high glucose concentrations. Studies of many glucose tolerant enzymes have been reported and due to the ongoing interest in these enzymes, here it has been reviewed this accumulated body of knowledge which provides valuable insights as to the kinetics, structure, regulation and evolution of glucose tolerant and glucose stimulated β-glucosidases. [ABSTRACT FROM AUTHOR]

The activity of the GH1 β-glucosidase from Humicola insolens (Bglhi) against p-nitrophenyl-β-D-glucopyranoside (pNP-Glc) and cellobiose is enhanced 2-fold by glucose and/or xylose. Kinetic and transglycosylation data showed that hydrolysis is preferred in the absence of monosaccharides. Stimulation involves allosteric interactions, increased transglycosylation and competition of the substrate and monosaccharides for the -1 glycone and the +1/+2 aglycone binding sites. Protein directed evolution has been used to generate 6 mutants of Bglhi with altered stimulation patterns. All mutants contain one of three substitutions (N235S, D237V or H307Y) clustered around the +1/+2 aglycone binding sites. Two mutants with the H307Y substitution preferentially followed the transglycosylation route in the absence of xylose or glucose. The strong stimulation of their pNP-glucosidase and cellobiase activities was accompanied by increased transglycosylation and higher monosaccharide tolerance. The D237V mutation favoured hydrolysis over transglycosylation and the pNP-glucosidase activity, but not the cellobiase activity, was stimulated by xylose. The substitution N235S abolished the preference for hydrolysis or transglycosylation; the cellobiase, but not the pNP-glucosidase activity of the mutants was strongly inhibited by xylose. Both the D237V and N235S mutations lowered tolerance to the monosaccharides. These results provide evidence that the fine modulation of the activity of Bglhi and mutants by glucose and/or xylose is regulated by the relative affinities of the glycone and aglycone binding sites for the substrate and the free monosaccharides. [ABSTRACT FROM AUTHOR]

Simple Summary: The most recent intergovernmental panel on climate change (IPCC 2021) has shown that the human influence on climate change has been unprecedented, predicting a global temperature increase of 1.5 °C in the earlies 2030s. The burning of fossil fuels has increased the emissions of nitrous oxide (N2O), methane (CH4), and carbon dioxide (CO2) to the atmosphere, amplifying the greenhouse effect in the last decades. In this scenario, the use of biorefineries, a renewable analog to petroleum refineries, has attracted a lot of attention since they use renewable sources as lignocellulosic feedstocks. However, climate change alters the temperature, rainfall patterns, drought, CO2 levels, and air moisture impacting biomass growth, productivity, chemical composition, and soil microbial community. Here, we discuss strategies to produce fuels and value-added products from biomass in a climate change scenario, potential feedstocks for bioenergy purposes, the chemical composition of lignocellulosic biomass, enzymes involved in biomass deconstruction, and other processes related to biomass production, processing, and conversion. Understanding these integrated factors involved in bioenergy production with plant responses to climate change shows that climate-smart agriculture is the only way to lower the negative impact of climate changes on crop adaptation and its use for bioenergy. The climate changes expected for the next decades will expose plants to increasing occurrences of combined abiotic stresses, including drought, higher temperatures, and elevated CO2 atmospheric concentrations. These abiotic stresses have significant consequences on photosynthesis and other plants' physiological processes and can lead to tolerance mechanisms that impact metabolism dynamics and limit plant productivity. Furthermore, due to the high carbohydrate content on the cell wall, plants represent a an essential source of lignocellulosic biomass for biofuels production. Thus, it is necessary to estimate their potential as feedstock for renewable energy production in future climate conditions since the synthesis of cell wall components seems to be affected by abiotic stresses. This review provides a brief overview of plant responses and the tolerance mechanisms applied in climate change scenarios that could impact its use as lignocellulosic biomass for bioenergy purposes. Important steps of biofuel production, which might influence the effects of climate change, besides biomass pretreatments and enzymatic biochemical conversions, are also discussed. We believe that this study may improve our understanding of the plant biological adaptations to combined abiotic stress and assist in the decision-making for selecting key agronomic crops that can be efficiently adapted to climate changes and applied in bioenergy production. [ABSTRACT FROM AUTHOR]