Understanding Interactions between Chemical Catalysts and Cell Wall Molecules

Chemical CatalystsThe structure of the cellulose microfibril, its size, crystallinity and potential aggregation in macrofibrils in plant cell walls, is a major factor in the recalcitrance of biomass to deconstruction. As prelude to the modulation of cellulose microfibril structure via genetic control, we developed computational models of cellulose structure defining hydrogen bond patterns, twist, temperature effects, and the effect of microfibril size in order to understand and enable prediction of intermolecular polymer behavior (Matthews et al. 2011, 2012a,b). We discovered that pretreatment with iron ion catalysts leads to multi-scale breakdown of cellulose structure creating individual cellulose chains, sub-fibrillar fragments, and twisted fibrils that remain intact and recalcitrant to further digestion (Wei et al. 2011, Inouye et al. 2014). We have quantified the effectiveness and identified mechanisms of iron ion catalyst pretreatment by using a 3D architectural analysis of nano-scale deconstruction of lignin and cellulose and increased surface area of cell walls within the 3D electron density field in electron tomography data sets (Ciesielski et al. 2013). This has led to a new way to construct atomistic models of cellulose microfibrils that incorporate directly measured curvature and twist.

Cell Wall MoleculesDirect addition of iron catalysts in biomass pretreatment is diffusion-limited, would increase cost and complexity of biorefinery unit operations, and may have deleterious environmental impacts. In vitro impregnation of recombinant soybean ferritin-Fe3+ into maize stover significantly increased glucose and xylose yields (Wei et al. in review). Therefore, we developed a genetic engineering strategy to deliver metal catalysts throughout the cell wall structure and so increase the effective surface area for catalysis of cellulose and xylan. We generated Arabidopsis and rice transformants expressing iron-binding peptides or ferritin, targeted intracellularly, or to the cell wall, and demonstrated increased Fe accumulation and sugar yields from these transgenic materials (Wei et al. in review, Yang et al. in review). Transgenic plants show significant increases in iron accumulation, biomass yield, and conversion efficiency relative to controls. In addition, transgenic rice grains show a 40% increase in seed yield and 35% increase in iron, and could potentially be used to address iron deficiency, the most common and widespread nutritional disorder according to the World Health Organization (Yang et al. in review).

References

Ciesielski PN, Matthews JF, Tucker MP, Beckham GT, Crowley MF, Himmel ME, Donohoe BS (2013) 3D electron tomography of pretreated biomass informs atomic modeling of cellulose microfibrils. ACS Nano 7:8011-8019.

Inouye H, Zhang Y, Yang L, Venugopalan N, Fischetti RF, Gleber SC, Vogt S, Fowle W, Makowski B, Tucker M, Ciesielski P, Donohoe B, Matthews J, Himmel ME, Makowski L (2014) Pretreatment deconstruction of nanoscale architecture in corn stover. Sci. Rep. 4: Art. No. 3756.

Matthews JF, Beckham GT, Bergenstråhle-Wohlert M, Brady JW, Himmel ME, Crowley MF (2012a) Comparison of cellulose Iβ simulations with three carbohydrate force fields. J. Chem. Theor. Comp. 8:735-748.

Matthews JF, Bergenstråhle M, Beckham GT, Himmel ME, Nimlos MR, Brady JW, Crowley MF (2011). High-temperature behavior of cellulose I. J. Phys. Chem. B 115:2155-2166.

Matthews JF, Himmel ME, Crowley MF (2012b) Conversion of cellulose Ia to Ib via a high temperature intermediate (I-HT) and other cellulose phase transformations. Cellulose 19:297-306.

Wei H, Donohoe BS, Vinzant TB, Ciesielski PN, Wang W, Gedvilas LM, Yeng YX, Johnson DK, Ding S-Y, Himmel ME, Tucker MP (2011) Elucidating the role of ferrous ion cocatalyst in enhancing dilute acid pretreatment of lignocellulosic biomass. Biotech. Biofuels 4: Art. No. 48.

Wei H, Yang H, Ciesielski PN, Donohoe BS, McCann MC, Murphy AS, Peer WA, Ding S-Y, Himmel ME, Tucker MP. The bio-availability of iron in plant cell walls enhances thermal chemical  pretreatments and saccharification. Biomass & Bioenergy (in review)

Yang H, Wei H, Ma G, Antunes M, Cox J, Zhang X, Liu X, Himmel ME, Tucker MP, McCann MC, Murphy AS, Peer WA. Targeted iron delivery produces a dual system for enhancement of biomass conversion and iron nutrition in rice. Nature Biotechnology(in review)

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