Contents lists available at ScienceDirect Biomass and Bioenergy journal homepage: www.elsevier.com/locate/biombioe Research paper Why does GH10 xylanase have better performance than GH11 xylanase for the deconstruction of pretreated biomass? Jinguang Hu a,b,* , Jack N. Saddler a a Forest Products Biotechnology and Bioenergy Group, Department of Wood Science, Faculty of Forestry, The University of British Columbia, 2424 Main Mall, Vancouver, BC, Canada b State Key Laboratory of Bioreactor Engineering, East China University of Science and Technology, 130 Meilong Road, Shanghai, 200237, China ARTICLE INFO Keywords: GH10 xylanase GH11 xylanase Synergism Bioconversion Lignocellulose Enzymatic hydrolysis ABSTRACT One approach to improve biomass deconstruction is to formulate a more efficient cellulase cocktail by adding “accessory enzymes” (e.g. xylanase/LPMO/laccases). Among different xylanases, glycoside hydrolase family 10 endo-xylanase (GH10EX) shows better performance than family 11 endo-xylanase (GH11EX) even though GH11EX has better kinetic activity on various xylan substrates. To better understand this phenomenon, the xylan accessibility of GH10/11 xylanases was assessed on various “model” and realistic cellulosic substrates and their thermostability was also compared during time course of hydrolysis. It showed that GH10EX had higher ac- cessibility towards the xylan backbone within pretreated biomass, especially for these with higher acetyl group content. Acetyl group removal could greatly intensify the synergistic cooperation between GH11EX and cellu- lases. Additionally, the higher thermostability of GH10EX appeared to be another reason for its outstanding potential during biomass decomposition. This work provides further insights for engineering better biocatalysts to enhance the economic viability of enzyme based biorefinery. 1. Introduction The cost-effective production of sugars from biomass continues to remain challenging, partly due to the relatively high enzyme/protein loading required to effectively hydrolyse the insoluble polysaccharides within the pretreated lignocellulosic substrates [1,2]. One way to re- duce the amount of enzyme usage is to improve the hydrolytic efficacy of “cellulase” mixtures by stimulating the cooperation among cellulases and various accessory enzymes such as xylanases and AA9 [3–7]. We and others have shown that the synergistic cooperation between cel- lulases and xylanases not only substantially enhanced the hydrolysis extent of both the glucan and xylan present in various pretreated lig- nocellulosic substrates, but also dramatically reduce the required cel- lulase dosage needed to achieve high cellulose hydrolysis yields (> 80%) [4,8,9]. Interestingly, when different glycoside hydrolase (GH) family endo-xylanases were compared, it appeared that family 10 endo-xylanase (GH10 EX) showed better synergistic cooperation with canonical hydrolytic cellulases than family 11 endo-xylanase (GH11 EX) on various pretreated substrates [8], even though GH11 EX was initially expected to be a better candidate for biomass deconstruction since it has relatively small size (easily access the xylan within the complex cellulose-hemicellulose-lignin matrix) and also higher cata- lytic activities on the “model” xylanolytic substrates such as the isolated birch wood and oat spelt xylan [8,10,11]. One of the major roles of xylanases was believed to remove xylan, which significantly restricts the accessibility of cellulose within the biomass to cellulase enzymes [4,10]. Xylan, the major hemicellulose component in hardwood and annual plants, is a diverse group of highly branched heteropolymers with a backbone of β-1,4-linked xylose re- sidues [12,13]. Xylan are often substituted with glucuronosyl or 4-O- methyl glucuronosyl residues at the C-2 position, in glucuronoxylans (GX), or substituted with arabinofuranosyl residues at the C-3 position, in arabinoxylan and/or glucuronoarabinoxylans (AX) [11,12,14]. In addition, most xylans are acetylated to various degrees (up to 10:7 ratio of xylose to acetyl), normally at the C-3 position on xylopyranose [13]. Although the commonly used thermochemical pretreatment processes can remove some of these xylan branches especially the glucuronosyl and arabinofuranosyl residues, leftover might still significantly impede the accessibility of the xylan backbone to the xylanase enzymes. Variants of steam-explosion pretreatments are currently utilized in several commercial biorefineries, such as Inbicon/Beta-renewables in Europe, Abengoa/Dupont/Poet-DSM in the United States, and GrandBio https://doi.org/10.1016/j.biombioe.2018.01.007 Received 4 November 2017; Received in revised form 1 January 2018; Accepted 17 January 2018 * Corresponding author. Forest Products Biotechnology and Bioenergy Group, Department of Wood Science, Faculty of Forestry, The University of British Columbia, 2424 Main Mall, Vancouver, BC, Canada. E-mail address: jinguang@mail.ubc.ca (J. Hu). Biomass and Bioenergy 110 (2018) 13–16 0961-9534/ © 2018 Elsevier Ltd. All rights reserved. T