Restructuring the Crystalline Cellulose Hydrogen Bond Network Enhances Its Depolymerization Rate
Restructuring the Crystalline Cellulose Hydrogen Bond Network Enhances Its Depolymerization Rate
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DOI：
10.1021/ja2011115
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发表时间：
2011-07-27
影响因子：
15
通讯作者：
Dale, Bruce E.
中科院分区：
文献类型：
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作者：
Chundawat, Shishir P. S.;Bellesia, Giovanni;Dale, Bruce E.
由于纤维素结晶度对酶促糖化的有害影响，木质纤维素向生物燃料的转化部分是低效的。我们展示了如何通过改变结晶纤维素原纤维内的氢键网络来增强纤维素酶的协同活性。我们通过分子动力学（MD）模拟和酶分析提供了这些现象的分子尺度的解释。氨将天然存在的结晶异晶型I-β转化为IIII，这导致纤维素层内氢键的数量减少和层间氢键的数量增加。纤维素IIII内的氢键网络的这种重排，使暴露于溶剂的葡聚糖链与水的氢键的数量增加了约50%，同时糖化速率提高了5倍（最接近无定形纤维素），最大表面结合纤维素酶能力降低了60-70%。表观纤维素酶活性的增强归因于纤维素IIII原纤维表面的“无定形样”性质，其促进更容易的葡聚糖链提取。不受限制的基板访问某些内切纤维素酶家族的活性位点裂缝进一步加速解构纤维素IIII。纤维素IIII的结构和动力学特征，揭示了MD模拟，纤维素晶体结构对原纤维表面水合作用，影响界面酶结合的作用提供了额外的见解。纤维素氢键网络内的细微变化提供了一种有吸引力的方式来增强其解构，并提供了对纤维素重结晶性质的独特见解。这种方法可以导致开发新的预处理和工程纤维素酶的非常规途径，用于经济高效的生物燃料生产。
Conversion of lignocellulose to biofuels is partly inefficient due to the deleterious impact of cellulose crystallinity on enzymatic saccharification. We demonstrate how the synergistic activity of cellulases was enhanced by altering the hydrogen bond network within crystalline cellulose fibrils. We provide a molecular-scale explanation of these phenomena through molecular dynamics (MD) simulations and enzymatic assays. Ammonia transformed the naturally occurring crystalline allomorph I-beta to IIII, which led to a decrease in the number of cellulose intrasheet hydrogen bonds and an increase in the number of intersheet hydrogen bonds. This rearrangement of the hydrogen bond network within cellulose IIII, which increased the number of solvent-exposed glucan chain hydrogen bonds with water by similar to 50%, was accompanied by enhanced saccharification rates by up to 5-fold (closest to amorphous cellulose) and 60-70% lower maximum surface-bound cellulase capacity. The enhancement in apparent cellulase activity was attributed to the "amorphous-like" nature of the cellulose IIII fibril surface that facilitated easier glucan chain extraction. Unrestricted substrate accessibility to active-site clefts of certain endocellulase families further accelerated deconstruction of cellulose IIII. Structural and dynamical features of cellulose IIII, revealed by MD simulations, gave additional insights into the role of cellulose crystal structure on fibril surface hydration that influences interfacial enzyme binding. Subtle alterations within the cellulose hydrogen bond network provide an attractive way to enhance its deconstruction and offer unique insight into the nature of cellulose recalcitrance. This approach can lead to unconventional pathways for development of novel pretreatments and engineered cellulases for cost-effective biofuels production.