SusChEM: Integrated Studies on Interactions between Lignocellulosic Fine Structure and Hydrolytic Enzymes toward Efficient Hydrolysis

木质纤维素植物生物质，如草秸秆和农业残留物，已被认为是一种低成本、丰富和可再生的可发酵糖来源，可用于生产燃料酒精和其他增值化学品。目前在纤维素生物燃料设施中部署的工艺使用酶的混合物将纤维素馏分转化为可发酵的糖。然而，这个过程仍然相当缓慢，并且是纤维素生物燃料生产中最昂贵的一步，部分原因是木质纤维素生物质对酶的攻击和分解是不耐受的。这种顽固性是由于木质纤维素在分子和微观水平上结构的复杂性。因此，在酶处理之前，对木质纤维素生物质进行预处理，通常使用蒸汽和化学物质的组合，以打开生物质中的孔隙，使酶更有效。有必要对生物质分解过程进行更好的分子水平的理解，以确定优化或消除预处理的新策略，提高转化率以实现成本降低。该项目的目标是在酶处理过程中对木质纤维素生物质如何分解或解构有一个基本的了解，以便确定这些新的节省成本的策略。本研究的创新之处在于将分子建模和分子化学成像相结合，以发现更多关于这一复杂过程的信息。与此项目相关的教育活动的特点是编写了一本关于将生物质转化为生物燃料的工作手册，用于夏季青年项目。木质纤维素生物质是纤维素、半纤维素和木质素的三维生物聚合物基质，从分子尺度到微观尺度都是有序的。长期以来，木质纤维素基质的复杂性一直被认为是制约其酶解成可发酵糖效率的关键因素。本研究将动态建模和分子成像相结合，以获得木质纤维素在使用水解酶混合物将生物质转化为糖的过程中分子和精细结构变化的实时动态的新见解。为了实现这一目标，本研究有三个目标。第一个目标是获得对木质纤维素生物质精细结构抵抗酶攻击的分子机制的基本定量理解。第二个目标是建立细胞壁成分组成和分子结构组织与水解工艺条件之间的关系，并将这些关系与生物质解构效率联系起来。第三个目标是开发一个机制建模框架，能够在综合考虑底物形态和成分分布的情况下模拟现实水解条件下的生物质解构。这些目标将通过原子力显微镜（AFM）的单分子成像和酶处理过程中生物质解构过程的受激拉曼散射（SRS）的化学成像来实现。该研究成果将有助于合理设计酶混合物和处理条件，以克服减缓水解反应的因素，从而优化水解生物反应器系统的设计，降低纤维素生物燃料制造系统的成本。

Lignocellulosic plant biomass such as grass straw and agricultural residues has been recognized a low-cost, abundant, and renewable source of fermentable sugars for production of fuel alcohol and other value-added chemicals. Current processes deployed in cellulosic biofuel facilities use a mixture of enzymes to convert the cellulosic fractions to fermentable sugars. However, this process is still fairly slow and is the most expensive step in cellulosic biofuels production, in part because lignocellulosic biomass is recalcitrant to enzymatic attack and breakdown. This recalcitrance is due to the complexity of lignocellulose structure at the molecular and microscopic levels. Therefore, before enzyme treatment, the lignocellulosic biomass is pretreated, typically with a combination of steam and chemicals, to open up the pores in the biomass so that the enzyme can be more effective. There is a need to develop a better, molecular level understanding of the biomass breakdown processes to identify new strategies optimize or eliminate pretreatment and improve the rate of conversion to realize cost reduction. The goal of this project is to develop a fundamental understanding of how lignocellulosic biomass is broken down, or deconstructed, during enzyme treatment so that these new cost-saving strategies can be identified. The innovative aspect of this study is the combination of molecular modeling and molecular chemical imaging to discover more about this complex process. The educational activities associated with this project feature the development of a workbook on the conversion of biomass to biofuels for use in summer youth programs.Lignocellulosic biomass is a three-dimensional biopolymer matrix of cellulose, hemicellulose, and lignin ordered at multiple scales ranging from the molecular scale to the microscale. The complexity of the lignocellulosic matrix has long been recognized as a key limiting factor in the efficiency of its enzymatic hydrolysis to fermentable sugars. This research will combine dynamic modeling and molecular imaging to gain new insights into the real-time dynamics of lignocellulosic molecular and fine structure changes during the conversion of lignocellulosic biomass to sugars using mixtures of hydrolytic enzymes. To accomplish this goal, the research has three objectives. The first objective is to gain a fundamental, quantitative understanding of the molecular mechanisms underlying the recalcitrance lignocellulosic biomass fine structure to enzymatic attack. The second objective is to establish relationships between cell wall component composition and molecular structural organization with hydrolysis processing conditions and correlate these relationships to biomass deconstruction efficiency. The third objective is to develop a mechanistic modeling framework capable of simulating biomass deconstruction under realistic hydrolysis conditions with comprehensive consideration of substrate morphology and component distribution. These objectives will be enabled through single-molecule imaging via Atomic Force Microscopy (AFM) and chemical imaging via Stimulated Raman Scattering (SRS) of the biomass deconstruction process during enzymatic treatment. Outcomes from the proposed research will enable the rational design of enzyme cocktails and processing conditions to overcome the factors that slow down the hydrolytic reactions, leading to optimal design of the hydrolysis bioreactor systems and cost reduction of cellulosic biofuel manufacturing systems.