β-Xylosidases: Structural Diversity, Catalytic Mechanism, and Inhibition by Monosaccharides

Abstract

Xylan, a prominent component of cellulosic biomass, has a high potential for degradation into reducing sugars, and subsequent conversion into bioethanol. This process requires a range of xylanolytic enzymes. Among them, β-xylosidases are crucial, because they hydrolyze more glycosidic bonds than any of the other xylanolytic enzymes. They also enhance the efficiency of the process by degrading xylooligosaccharides, which are potent inhibitors of other hemicellulose-/xylan-converting enzymes. On the other hand, the β-xylosidase itself is also inhibited by monosaccharides that may be generated in high concentrations during the saccharification process. Structurally, β-xylosidases are diverse enzymes with different substrate specificities and enzyme mechanisms. Here, we review the structural diversity and catalytic mechanisms of β-xylosidases, and discuss their inhibition by monosaccharides.

Xylanolytic Extremozymes Retrieved From Environmental Metagenomes: Characteristics, Genetic Engineering, and Applications

“…Existing β-xylosidases are associated with several limitations, such as poor efficiency, low thermostability, salt sensitivity, and by-product inhibition (Bao et al, 2012;Anand et al, 2013). Therefore, efforts have been made to discover novel candidates of β-xylosidases using metagenomic approaches, with which little success has been achieved (Wagschal et al, 2009;Jordan et al, 2016;Cheng et al, 2017;Sato et al, 2017;Liu et al, 2018;Rohman et al, 2019; Table 2). Of the available metagenomic β-xylosidases, fewer than 20 have been extensively characterized to date.…”

“…Several β-xylosidases and metagenomic β-xylosidases have also been identified for their bifunctional enzymatic activities ( DeCastro et al, 2016 ; Rohman et al, 2019 ). Such β-xylosidases find applicability in bioethanol production along with the endo-xylanases for efficient release of sugars from the hemicellulose component of agro-residues ( Sae-Lee and Boonmee, 2014 ; Wang et al, 2015 ).…”

Characterisation of the Effect of the Spatial Organisation of Hemicellulases on the Hydrolysis of Plant Biomass Polymer

“…It is clear that X 3 is produced at the very first step of the reaction, while X 1 started to be accumulated after 60 min of reaction ( Figure S7). Accumulation of X 3 by a xylan GH11 degrading enzyme is a marker of a xylanase activity [56], just like X 1 is for GH43 [57]. This observation reflects the fact that enough small oligosaccharides have to be produced by the xylanase first before being hydrolysed by the xylosidase.…”

Co-production of Xylooligosaccharides and Xylose From Poplar Sawdust by Recombinant Endo-1,4-β-Xylanase and β-Xylosidase Mixture Hydrolysis

“…Merely, the thermostability of endo-1,4-β-xylanases from filamentous fungi can be improved by genetic engineering; thereby, the application scope of the filamentous fungi endo-1,4-β-xylanases is greatly extended (Li et al, 2019c ). All the β-xylosidases are mainly divided into GH1, GH3, GH30, GH39, GH43, GH52, GH54, and GH120 (Rohman et al, 2019 ). However, most β-xylosidases, especially the β-xylosidases belonging to GH3, are sensitive and inhibited to xylose by feedback, which limits its practical application.…”