Nicole R. Brown

Covalent bond formation between amino acids and lignin: Cross-coupling between proteins and lignin

The present study characterized the products formed from the reaction of amino acids and in turn, proteins, with lignin resulting in cross-coupling. When added to reaction mixtures containing coniferyl alcohol, horseradish peroxidase and H2O2, three amino acids (Cys, Tyr, and Thr) are able to form adducts. The low molecular weight products were analyzed by HPLC and from each reaction mixture, one product was isolated and analyzed by LC/MS. LC/MS results are consistent with bond formation between the polar side-chain of these amino acids with Cα. These results are consistent with the cross-coupling of Cys, Tyr and Thr through a quinone methide intermediate. In addition to the free amino acids, it was found that the cross-coupling of proteins with protolignin through Cys or Tyr residues. The findings provide a mechanism by which proteins and lignin can cross-couple in the plant cell wall.

Microtubule asters as templates for nanomaterials assembly.

Self organization of the kinesin-microtubule system was implemented as a novel template to create percolated nanofiber networks. Asters of microtubule seeds were immobilized on glass surfaces and their growth was recorded over time. The individual aster islands became interconnected as microtubules grew and overlapped, resulting in a highly percolated network. Cellulose nanowhiskers were used to demonstrate the application of this system to nanomaterials organization. The size distribution of the cellulose nanowhiskers was comparable to that of microtubules. To link cellulose nanowhiskers to microtubules, the nanowhiskers were functionalized by biotin using cellulose binding domains. Fluorescence studies confirmed biotinylation of cellulose nanowhiskers and binding of cellulose nanowhiskers to biotinylated microtubules.

Towards lignin-protein crosslinking: amino acid adducts of a lignin model quinone methide

The polyaromatic structure of lignin has long been recognized as a key contributor to the rigidity of plant vascular tissues. Although lignin structure was once conceptualized as a highly networked, heterogeneous, high molecular weight polymer, recent studies have suggested a very different configuration may exist in planta. These findings, coupled with the increasing attention and interest in efficiently utilizing lignocellulosic materials for green materials and energy applications, have renewed interest in lignin chemistry. Here we focus on quinone methides (QMs)—key intermediates in lignin polymerization—that are quenched via reaction with cell-wall-available nucleophiles. Reactions with alcohol and uronic acid groups of hemicelluloses, for example, can lead to lignin-carbohydrate crosslinks. Our work is a first step toward exploring potential QM reactions with nucleophilic groups in cell wall proteins. We conducted a model compound study wherein the lignin model compound guaiacylglycerol-β-guaiacyl ether 1, was converted to its QM 2, then reacted with amino acids bearing nucleophilic side-groups. Yields for the QM-amino acid adducts ranged from quantitative in the case of QM-lysine 3, to zero (no reaction) in the cases of QM-threonine (Thr) 10 and QM-hydroxyproline (Hyp) 11. The structures of the QM-amino acid adducts were confirmed via 1D and 2D nuclear magnetic resonance (NMR) spectroscopy and density functional theory (DFT) calculations, thereby extending the lignin NMR database to include amino acid crosslinks. Some of the QM-amino acid adducts formed both syn- and anti-isomers, whereas others favored only one isomer. Because the QM-Thr 10 and QM-Hyp 11 compounds could not be experimentally prepared under conditions described here but could potentially form in vivo, we used DFT to calculate their NMR shifts. Characterization of these model adducts extends the lignin NMR database to aid in the identification of lignin-protein linkages in more complex in vitro and in vivo systems, and may allow for the identification of such linkages in planta.

Wood chemistry analysis and expression profiling of a poplar clone expressing a tyrosine-rich peptide

Key messageOur study has identified pathways and gene candidates that may be associated with the greater flexibility and digestibility of the poplar cell walls.AbstractWith the goal of facilitating lignin removal during the utilization of woody biomass as a biofuel feedstock, we previously transformed a hybrid poplar clone with a partial cDNA sequence encoding a tyrosine- and hydroxyproline-rich glycoprotein from parsley. A number of the transgenic lines released more polysaccharides following protease digestion and were more flexible than wild-type plants, but otherwise normal in phenotype. Here, we report that overexpression of the tyrosine-rich peptide encoding sequence in these transgenic poplar plants did not significantly alter total lignin quantity or quality (S/G lignin ratio), five- and six-carbon sugar contents, growth rate, or susceptibility to a major poplar fungal pathogen, Septoria musiva. Whole-genome microarray analysis revealed a total of 411 differentially expressed transcripts in transgenic lines, all with decreased transcript abundance relative to wild-type plants. Their corresponding genes were overrepresented in functional categories such as secondary metabolism, amino acid metabolism, and energy metabolism. Transcript abundance was decreased primarily for five types of genes encoding proteins involved in cell-wall organization and in lignin biosynthesis. The expression of a subset of 19 of the differentially regulated genes by qRT-PCR validated the microarray results. Our study has identified pathways and gene candidates that may be the underlying cause for the enhanced flexibility and digestibility of the stems of poplar plants expressing the TYR transgene.

Lignin Cross-Links with Cysteine- and Tyrosine-Containing Peptides under Biomimetic Conditions

The work presented here investigates the cross-linking of various nucleophilic amino acids with lignin under aqueous conditions, thus providing insight as to which amino acids might cross-link with lignin in planta. Lignin dehydrogenation polymer (DHP) was prepared in aqueous solutions that contained tripeptides with the general structure XGG, where X represents an amino acid with a nucleophilic side chain. Fourier-transform infrared spectroscopy and energy dispersive X-ray spectroscopy showed that peptides containing cysteine and tyrosine were incorporated into the DHP to form DHP-CGG and DHP-YGG adducts, whereas peptides containing other nucleophilic amino acids were not incorporated. Scanning electron microscopy showed that the physical morphology of DHP was altered by the presence of peptides in the aqueous solution, regardless of peptide incorporation into the DHP. Nuclear magnetic resonance (NMR) spectroscopy showed that cysteine-containing peptide cross-linked with lignin at the lignin α-position, whereas in the case of the lignin-tyrosine adduct the exact cross-linking pathway could not be determined. This is the first study to use NMR to confirm cross-linking between lignin and peptides under biomimetic conditions. The results of this study may indicate the potential for lignin-protein linkage formation in planta, particularly between lignin and cysteine- and/or tyrosine-rich proteins.

Resin Suppliers' Perspectives on the “Greening” of the North American Interior Wood Composite Panel Market

Eight North American resin suppliers, representing 100 percent of the polymeric diphenylmethane diisocyanate (pMDI) market and >95 percent of the urea-formaldehyde (UF) market for interior wood composite panels (IWCPs), participated in an exploratory phone survey conducted in July and August 2008 that was designed to better understand their product positioning and “green” resin strategies. These eight firms were identified as the largest suppliers to the IWCP industry, which includes particleboard, medium density fiberboard, hardwood plywood, and hardboard. In 2007, the IWCP resin industry was highly concentrated and dominated by UF resins. Resin suppliers rated research and development work and technical support as the most important competitive advantage factors they used. Moreover, resin suppliers perceived the following product and service attributes to have the greatest importance to their IWCP customers: low formaldehyde emissions from finished panels (4.8 of 5), fast resolution of customer complain...

Effect of maleic anhydride polypropylene copolymer addition on the physical and mechanical properties of polymeric diphenylmethane diisocyanate-bonded oriented strand board panels.

The effect of varying proportions of maleic anhydride polypropylene (MAPP) on the physical and mechanical properties of polymeric diphenylmethane diisocyanate (pMDI)-bonded oriented strand board panels was investigated. Additionally, two forms of MAPP (powder and emulsion) were used to determine the effect of MAPP type on panel properties. Panels were produced by combining southern yellow pine (Pinus spp.) flakes with 4 percent pMDI binder and 0, 1.5, 3, 4.5, or 6 percent powdered or emulsified MAPP. Addition of emulsified MAPP decreased panel mechanical properties regardless of addition level. Powdered MAPP had a negligible effect on panel modulus of elasticity and only produced significant decreases in panel modulus of rupture and internal bond strength at the highest addition level (6%). Emulsified MAPP effected greater reductions in panel mechanical properties relative to powdered MAPP. Increasing levels of emulsified MAPP caused undesirable increases in both 24-hour water absorption and thickness swelling. Powdered MAPP did not provide a significant improvement over control panels in water absorption and thickness swell tests. Addition of either powdered or emulsified MAPP appeared to have a negligible effect on panel permeance.