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The derivation of second-generation biofuels from non-edible biomass is viewed as crucial for establishing a sustainable bio-based economy for the future. The inertness of lignocellulosic biomass makes its breakdown for conversion into fuels and other compounds a challenge. Enzyme cocktails can be utilized in the bio-refinery for lignocellulose deconstruction but until recently their costs were regarded as high. Lytic polysaccharide monooxygenases (LPMOs) offer tremendous promise for further process improvements owing to their ability to boost the activity of biomass-degrading enzyme consortia. Combining data from multiple disciplines, progress has been made in understanding the biochemistry of LPMOs. We review the academic literature in this area and highlight some of the key questions that remain., (Copyright © 2015 Elsevier Ltd. All rights reserved.)

The biological conversion of lignocellulosic matter into high‐value chemicals or biofuels is of increasing industrial importance as the sector slowly transitions away from nonrenewable sources. Many industrial processes involve the use of cellulolytic enzyme cocktails – a selection of glycoside hydrolases and, increasingly, polysaccharide oxygenases – to break down recalcitrant plant polysaccharides. ORFs from the genome of Teredinibacter turnerae, a symbiont hosted within the gills of marine shipworms, were identified in order to search for enzymes with desirable traits. Here, a putative T. turnerae glycoside hydrolase from family 8, hereafter referred to as TtGH8, is analysed. The enzyme is shown to be active against β‐1,4‐xylan and mixed‐linkage (β‐1,3,β‐1,4) marine xylan. Kinetic parameters, obtained using high‐performance anion‐exchange chromatography with pulsed amperometric detection and 3,5‐dinitrosalicyclic acid reducing‐sugar assays, show that TtGH8 catalyses the hydrolysis of β‐1,4‐xylohexaose with a kcat/Km of 7.5 × 107 M−1 min−1 but displays maximal activity against mixed‐linkage polymeric xylans, hinting at a primary role in the degradation of marine polysaccharides. The three‐dimensional structure of TtGH8 was solved in uncomplexed and xylobiose‐, xylotriose‐ and xylohexaose‐bound forms at approximately 1.5 Å resolution; the latter was consistent with the greater kcat/Km for hexasaccharide substrates. A 2,5B boat conformation observed in the −1 position of bound xylotriose is consistent with the proposed conformational itinerary for this class of enzyme. This work shows TtGH8 to be effective at the degradation of xylan‐based substrates, notably marine xylan, further exemplifying the potential of T. turnerae for effective and diverse biomass degradation. [ABSTRACT FROM AUTHOR]

The enzymatic deconstruction of recalcitrant polysaccharide biomass is central to the conversion of these substrates for societal benefit, such as in biofuels. Traditional models for enzyme-catalysed polysaccharide degradation involved the synergistic action of endo-, exo- and processive glycoside hydrolases working in concert to hydrolyse the substrate. More recently this model has been succeeded by one featuring a newly discovered class of mononuclear copper enzymes: lytic polysaccharide monooxygenases (LPMOs; classified as Auxiliary Activity (AA) enzymes in the CAZy classification). In 2013, the structure of an LPMO from Bacillus amyloliquefaciens, BaAA10, was solved with the Cu centre photoreduced to Cu(i) in the X-ray beam. Here we present the catalytic activity of BaAA10. We show that it is a chitin-active LPMO, active on both α and β chitin, with the Cu(ii) binding with low nM KD, and the substrate greatly increasing the thermal stability of the enzyme. A spiral data collection strategy has been used to facilitate access to the previously unobservable Cu(ii) state of the active centre, revealing a coordination geometry around the copper which is distorted from axial symmetry, consistent with the previous findings from EPR spectroscopy. [ABSTRACT FROM AUTHOR]

Complex carbohydrates are ubiquitous in all kingdoms of life. As major components of the plant cell wall they constitute both a rich renewable carbon source for biotechnological transformation into fuels, chemicals and materials, and also form an important energy source as part of a healthy human diet. In both contexts, there has been significant, sustained interest in understanding how microbes transform these substrates. Classical perspectives of microbial polysaccharide degradation are currently being augmented by recent advances in the discovery of lytic polysaccharide monooxygenases (LPMOs) and polysaccharide utilization loci (PULs). Fundamental discoveries in carbohydrate enzymology are both advancing biological understanding, as well as informing applications in industrial biomass conversion and modulation of the human gut microbiota to mediate health benefits. [ABSTRACT FROM AUTHOR]