The pattern of xylan acetylation suggests xylan may interact with cellulose microfibrils as a twofold helical screw in the secondary plant cell wall of Arabidopsis thaliana.

The interaction between xylan and cellulose microfibrils is important for secondary cell wall properties in vascular plants; however, the molecular arrangement of xylan in the cell wall and the nature of the molecular bonding between the polysaccharides are unknown. In dicots, the xylan backbone of β-(1,4)-linked xylosyl residues is decorated by occasional glucuronic acid, and approximately one-half of the xylosyl residues are O-acetylated at C-2 or C-3. We recently proposed that the even, periodic spacing of GlcA residues in the major domain of dicot xylan might allow the xylan backbone to fold as a twofold helical screw to facilitate alignment along, and stable interaction with, cellulose fibrils; however, such an interaction might be adversely impacted by random acetylation of the xylan backbone. Here, we investigated the arrangement of acetyl residues in Arabidopsis xylan using mass spectrometry and NMR. Alternate xylosyl residues along the backbone are acetylated. Using molecular dynamics simulation, we found that a twofold helical screw conformation of xylan is stable in interactions with both hydrophilic and hydrophobic cellulose faces. Tight docking of xylan on the hydrophilic faces is feasible only for xylan decorated on alternate residues and folded as a twofold helical screw. The findings suggest an explanation for the importance of acetylation for xylan-cellulose interactions, and also have implications for our understanding of cell wall molecular architecture and properties, and biological degradation by pathogens and fungi. They will also impact strategies to improve lignocellulose processing for biorefining and bioenergy.The work conducted by TT and NN was supported by a grant from the BBSRC: BB/G016240/1 BBSRC Sustainable Energy Centre Cell Wall Sugars Programme (BSBEC) to PD and DNB. The work of PD was supported by the European Community’s Seventh Framework Programme SUNLIBB (FP7/2007-2013) under the grant agreement #251132. The NMR facility infrastructure was supported by the BBSRC and the Wellcome Trust. TCFG thanks CNPq (Brazil) for a graduate fellowship (grant # 140978/2009-7). MSS thanks CEPROBIO (grant # 490022/2009- 0) and FAPESP for funding (grant #2013/08293-7).This is the accepted version of the following article: "Busse-Wicher, M; Gomes, T.C.F; Tryfona, T; Nikolovski, N; Stott, K; Grantham, N.J; Bolam, D.N; Skaf, M.S; Dupree, P. (2014) "The pattern of xylan acetylation suggests xylan may interact with cellulose microfibrils as a two-fold helical screw in the secondary plant cell wall of Arabidopsis thaliana." The Plant Journal. Accepted article [electronic] 10.1111/tpj.12575", which has been published in final form at http://onlinelibrary.wiley.com/doi/10.1111/tpj.12575/abstrac

Glycan complexity dictates microbial resource allocation in the large intestine.

The structure of the human gut microbiota is controlled primarily through the degradation of complex dietary carbohydrates, but the extent to which carbohydrate breakdown products are shared between members of the microbiota is unclear. We show here, using xylan as a model, that sharing the breakdown products of complex carbohydrates by key members of the microbiota, such as Bacteroides ovatus, is dependent on the complexity of the target glycan. Characterization of the extensive xylan degrading apparatus expressed by B. ovatus reveals that the breakdown of the polysaccharide by the human gut microbiota is significantly more complex than previous models suggested, which were based on the deconstruction of xylans containing limited monosaccharide side chains. Our report presents a highly complex and dynamic xylan degrading apparatus that is fine-tuned to recognize the different forms of the polysaccharide presented to the human gut microbiota.This work was supported in part by grants to D.N.B. (BBSRC BB/G016186/1) and H.J.G. (Wellcome Trust WT097907AIA).This is the final version. It was first published by NPG at http://dx.doi.org/10.1038/ncomms848

Structure and boosting activity of a starch-degrading lytic polysaccharide monooxygenase.

Lytic polysaccharide monooxygenases (LPMOs) are recently discovered enzymes that oxidatively deconstruct polysaccharides. LPMOs are fundamental in the effective utilization of these substrates by bacteria and fungi; moreover, the enzymes have significant industrial importance. We report here the activity, spectroscopy and three-dimensional structure of a starch-active LPMO, a representative of the new CAZy AA13 family. We demonstrate that these enzymes generate aldonic acid-terminated malto-oligosaccharides from retrograded starch and boost significantly the conversion of this recalcitrant substrate to maltose by β-amylase. The detailed structure of the enzyme's active site yields insights into the mechanism of action of this important class of enzymes.This work was supported by a grant from the European Research Agency—Industrial Biotechnology Initiative as financed by the national research councils: Biotechnology and Biological Sciences Research Council (grant number BB/L000423) and Agence Française de l'Environnement et de la Maîtrise de l'Energie (grant number 1201C102). The Danish Council for Strategic Research (grant numbers 12-134923 and 12-134922). The Danish Ministry of Higher Education and Science through the Instrument Center DANSCATT and the European Community’s Seventh Framework Programme (FP7/2007-2013) under BioStruct-X (grant agreement N°283570) funded travel to synchrotrons. P.H.W. acknowledges the experimental assistance of Rebecca Gregory and Dr Victor Chechik. L.L.L. acknowledges the experimental assistance of Dorthe Boelskifte and the ESRF and MAXLAB staff for assistance with data collection.This is the final version of the article. It first appeared from NPG via http://dx.doi.org/10.1038/ncomms696

CHOROCHRONOS - Research on spatio-temporal database systems

Spatiotemporal database management systems can be-come an enabling technology for important applications such as Geographic Information Systems (GIS), environ-mental information systems, and multimedia. In this paper we address research issues in spatiotemporal databases, by providing an analysis of the challenges set, the prob-lems encountered, as well as the proposed solutions and the envisioned research areas open to investigation in the EU funded project CHOROCHRONOS. 1