Abstract
The enzymatic hydrolysis of complex plant biomass is a major societal goal of the 21st century in order to deliver renewable energy from nonpetroleum and nonfood sources. One of the major problems in many industrial processes, including the production of second-generation biofuels from lignocellulose, is the presence of `hemicelluloses' such as xylans which block access to the cellulosic biomass. Xylans, with a polymeric β-1,4-xylose backbone, are frequently decorated with acetyl, glucuronyl and arabinofuranosyl `side-chain' substituents, all of which need to be removed for complete degradation of the xylan. As such, there is interest in side-chain-cleaving enzymes and their action on polymeric substrates. Here, the 1.25 Å resolution structure of the Talaromyces pinophilus arabinofuranosidase in complex with the inhibitor AraDNJ, which binds with a Kd of 24 ± 0.4 µM, is reported. Positively charged iminosugars are generally considered to be potent inhibitors of retaining glycosidases by virtue of their ability to interact with both acid/base and nucleophilic carboxylates. Here, AraDNJ shows good inhibition of an inverting enzyme, allowing further insight into the structural basis for arabinoxylan recognition and degradation.
Highlights
The production of ‘second-generation’ biofuels, i.e. from nonfood plants, is a major societal goal as we move away from petroleum-based energy towards secure and renewable energy
The 1.25 Aresolution structure of the Talaromyces pinophilus arabinofuranosidase in complex with the inhibitor AraDNJ, which binds with a Kd of 24 Æ 0.4 mM, is reported
The majority of polysaccharide biomass in plants is cellulose, the cellulose fibres are coated with hemicelluloses such as xylan, which render access to the cellulose more difficult
Summary
The production of ‘second-generation’ biofuels, i.e. from nonfood plants, is a major societal goal as we move away from petroleum-based energy towards secure and renewable energy. Given that arabinoxylan degradation requires a consortium of enzymes acting in partial synergy, most elegantly emphasized through Gilbert’s recent work on xylan degradation by the microbiota (Rogowski et al, 2015), there is much interest in the structure, mechanism and specificity of xylan-active enzymes, with a special focus on side-chain-cleaving enzymes and their potential synergy with backbone-cleaving xylanases. This potential synergy is further complicated by the differing capacities of the endoxylanases themselves to accommodate side chains. The complex sheds light on the active site and, in light of previously published data, allows analysis of how the enzyme interacts with arabinoxylan substrates, serving to remove these side chains from the xylan backbone
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