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Analysis of Lignin Interactions and Breakdown in Plant Cell Walls by Solid-State Nuclear Magnetic Resonance: Towards More Efficient Biomass Pathways

Primary Supervisor: Professor Steven P. Brown, Department of Physics

Secondary supervisor: Professor Tim Bugg, Department of Chemistry

PhD project title: Analysis of Lignin Interactions and Breakdown in Plant Cell Walls by Solid-State Nuclear Magnetic Resonance: Towards More Efficient Biomass Pathways

University of Registration: University of Warwick

Project outline:

Yielding insight into structure and dynamics at atomic scale in complex biological systems is a major challenge for analytical science. Nuclear magnetic resonance (NMR) is a powerful probe of structure and dynamics that exploits the inherent magnetism of atomic nuclei and their fine sensitivity to local magnetic fields arising from their electronic environment as well as the presence of other nearby magnetic nuclei. A great strength of NMR is hence the potential for exquisite atomic-scale resolution. This project will apply NMR in the solid state to a key biological application, namely to understand the role of lignin in plant cell walls, in particular with the aim of better understanding enzymatic breakdown pathways that target the lignin; this is of key importance for improving the process of freeing up energy from plant biomass, but has more general relevance for enhancing our understanding of plant cell wall make-up more widely.

This project builds upon world-leading expertise in experimental solid-state NMR, plant cell walls and lignin breakdown enzymes in the groups of Professors Brown and Bugg in the Departments of Physics and Chemistry, respectively, at the University of Warwick and our key collaborator, Professor Dupree in the Department of Biochemistry at the University of Cambridge. You will access state-of-the-art infrastructure in the exceptionally well equipped University of Warwick solid-state NMR laboratory that hosts the UK High-Field Solid-State NMR National Research Facility (a 1 GHz instrument, the highest magnetic field for NMR in the UK, is at field since 2020).

13C labelling is a pre-requisite for the application of advanced solid-state NMR methodologies to plant cell walls. As an example of the power of this methodology, the Dupree and Brown and groups in Cambridge and Warwick have unearthed unambiguous experimental evidence for a specific mode of xylose-cellulose interaction in plant cell walls [1]. This project will focus on the spatial relationship between lignin and polysaccharides in cell walls: the Cambridge laboratory will provide samples such as 13C labelled spruce and pine wood, which has G-lignin that consists of polymerised coniferyl alcohol, as well as the model Arabidopsis plant: mutants with altered lignin structures can be grown, providing useful controls and samples to understand enzyme specificity and action, for example comparing cad2/6 aldehyde-rich lignin to wild-type plants with both S and G lignin. The feasibility of our approach is illustrated by a recent publication by the Wang group in the U.S. which tabulates 13C solid-state NMR chemical shifts of G, S and H lignin in arabidopsis, maize, and rice plants [2]. There is scope to complement experimental work with calculations based on molecular dynamics and density-functional theory (as employed, e.g. in ref. [1]).

In complementary research, the Bugg group has identified various bacterial lignin-oxidising enzymes, e.g., an unusual manganese superoxide dismutase enzyme from Sphingobacterium ap. T2 that can attack polymeric lignin [3]. Although the Bugg group have used these enzymes to generate low molecular weight products from lignin oxidation, much less is known about the often insoluble residual oxidised high molecular weight lignin residue. A starting point for solid-state NMR analysis will be an already-prepared synthetic DHP lignin containing a 13C label at the b-carbon of the aliphatic sidechain. Treatment of this 13C-labelled lignin with different lignin-oxidising enzymes would allow us to determine which mode of lignin oxidation was taking place.

In summary, through this multi-disciplinary project, you will gain expertise in plant cell wall and lignin biochemistry and biophysics, and develop skills and experience in advanced solid-state NMR as well as related experimental and computational approaches.

References:

  1. Folding of xylan onto cellulose fibrils in plant cell walls revealed by solid-state NMR"

    Simmons et al, Nature Communications 7, 13902 (2016)

  2. Lignin-polysaccharide interactions in plant secondary cell walls revealed by solid-state NMR" Kang et al, Nature Communications 10, 347 (2019)

  3. Sphingobacterium sp. T2 manganese superoxide dismutase catalyses the oxidative demethylation of polymeric lignin via generation of hydroxyl radical"

    Rashid et al, ACS Chem. Biol., 13, 2920 (2018)

BBSRC Strategic Research Priority: Sustainable Agriculture and Food: Plant and Crop Science. Renewable Resources and Clean Growth: Bio-energy. Understanding the Rules of Life: Plant Science

    Techniques that will be undertaken during the project:

    In Brown’s group: experimental solid-state Nuclear Magnetic Resonance (NMR) and Related computational analysis, e.g., using density-functional theory and molecular dynamics; In Bugg’s group, enzyme purification and biotransformations.

    Contact: Professor Steven Brown, University of Warwick