An international team of researchers has discovered a new family of enzymes found in fungi (fungal lytic polysaccharide monooxygenases, LPMOs) that are capable of breaking down xylans—a recalcitrant polysaccharide abundant in wood biomass.
The enzymes could now potentially be used to sustainably convert wood biomass into valuable chemical commodities such as biofuels. A paper on their discovery is published in the journal Nature Chemical Biology.
In bio-based industries, the use of wood is taking on a new importance, as it constitutes the most promising source for advanced biofuels and plant-derived products. Notwithstanding its potential, however, the cost-effective conversion of woody feedstocks is limited by a single key factor, the recalcitrance of the lignocellulosic matrix to degradation by enzyme cocktails. To overcome this recalcitrance, biorefineries utilize energy-demanding pretreatment processes to solubilize the inaccessible biomass components before enzymatic saccharification. The recalcitrant fraction reflects its heteroxylan content, which is known to be particularly resistant to xylanases due to extensive decoration and because these xylans can adopt a flat conformation, with their chains solidly adhering via hydrogen bonds to the surface of cellulose microfibrils. Finding sustainable means to overcome this resistance to degradation is one of the main challenges faced by modern biorefineries. Indeed, the xylan problem is so severe that consideration is being given to engineering energy crops modified to contain fewer recalcitrant xylans.
… Using comparative post-genomic approaches among fungal wood decayers, we identified the existence of a previously unknown family of LPMOs. This new family, to be termed AA14 in the CAZy classification, differs phylogenetically and structurally from the previous AA9, AA10, AA11 and AA13 families. The first characterized members from the white-rot basidiomycete fungus P. coccineus target xylan chains covering wood cellulose fibers, thus unlocking the enzymatic degradation of wood biomass.—Couturier et al.
Fungi play a significant role in ecosystems in breaking down wood within the carbon cycle, releasing nutrients back into soil. This property of fungi inspired the researchers to investigate the mechanisms that allow this process to take place.
Back in 2010 we made the key discovery that a group of enzymes found in fungi, contain copper – these enzymes are now known to be an important component in the decomposition of biomass by biology. This research builds on that work by identifying further enzymes from this class which have the ability to break down wood’s challenging molecular structure.
These enzymes may underpin the development of improved enzyme cocktails for biorefinery applications using wood—unlocking its conversion into a wide-range of valuable commodities in a sustainable way.—Professor Paul Walton from the Department of Chemistry at the University of York, co-author
The researchers isolated the enzymes from fungi that play a vital role in the terrestrial carbon cycle and dominate wood decomposition in forests.
Marie Couturier, Simon Ladevèze, Gerlind Sulzenbacher, Luisa Ciano, Mathieu Fanuel, Céline Moreau, Ana Villares, Bernard Cathala, Florence Chaspoul, Kristian E Frandsen, Aurore Labourel, Isabelle Herpoël-Gimbert, Sacha Grisel, Mireille Haon, Nicolas Lenfant, Hélène Rogniaux, David Ropartz, Gideon J Davies, Marie-Noëlle Rosso, Paul H Walton, Bernard Henrissat & Jean-Guy Berrin (2018) “Lytic xylan oxidases from wood-decay fungi unlock biomass degradation” Nature Chemical Biology volume 14, pages 306–310 doi: 10.1038/nchembio.2558