木质纤维素材料预处理过程中木质素结构和性质的变化及其对纤维素酶吸附的影响及机制

Due to the limited availability of fossil carbon,as well as environmental concerns, comprehensive utilization of lignocellulosics for fuel and chemical production has currently raised much interest. A key step for bioconversion of lignocellulosic materials to fuels and chemcials is that the cellulose and hemicelluloses are first hydrolyzed by enzymes to fermentable sugars. But the recalcitrant structure of lignocellulose, which is caused by avariety of factors such as the inaccessibility of the cellulose, due to its close association with the hemicelluloses and lignin, crystallinity, etc., makes it dif?cult to hydrolyze enzymatically.Therefore,lignocellulosic materials must ?rst be pretreated to improve enzymatic hydrolysis.In the proposed pretreatment methods, pretreatment with dilute sulfuric acid is common method. The hemicellulose was dissolved out during the acid pretreatment,and accessibility of cellulose was improved. However, the residual lignin remaining in the pretreated cellulosic substrates signi?cantly in?uences subsequent enzymatic hydrolysis as lignin acts as both a physical barrier,.restricting access of cellulases to cellulose, and as an attractant to cellulases,.resulting in non-productive binding. The physical/chemical characteristics of lignin were also changed by dilute acid pretreatment. It has been shown that the chemical and physical structure of lignin plays a significant role in determining the magnitude of inhibition it contributes to hydrolysis. But to date, less research has been conducted on the adsorption features of different protein in cellulase enzyme systems to ligin, the relationship between the structures and properties of lignin and adsorption of cellulase to lignin, and effect of pretreatment process on adsorption of cellulase to lignin.In the project, the residual lignin were isolated from dilute acid pretreated wood and nonwood biomass materials, and structurally characterized. The changes of lignin contents and properties of lignin in the cellulosic substrates before and after pretreatment, the adsorption rules of different protein in cellulase enzyme systems to lignin, and the effect of dilute acid preteatment on adsorption of cellulases to lignin and its mechanism,etc., were studied.It was valuable for finding suibable methods to decrease lignin inhibitory effect, improving enzymatic-hydrolysis of lignocellulose by adding essential enzyme components and reconstruction of the composition of the enzyme systems.

将资源丰富且可再生的木质纤维素通过生物转化生产液体燃料和大宗化学品，是当前研究的热点。生物质生物转化的关键步骤是首先将碳水化合物利用酶水解生成单糖。但木质素的存在抑制了纤维素的酶水解，因为它既作为物理屏障限制酶接近纤维素，又能吸附纤维素酶导致非反应性的结合。预处理是改善纤维素酶解性的最要一步，预处理过程中木质素的含量、结构和性质等将发生变化。但至今为止，木质素对纤维素酶复杂组分中不同蛋白的吸附特征尚不清楚，木质素结构和性质与纤维素酶吸附之间的相互关系以及预处理对木质素吸附纤维素酶的影响和机制尚未阐明。针对上述问题，本项目将系统地开展预处理对木材和非木材原料中木质素结构和性质等的影响、木质素对纤维素酶不同蛋白的吸附特征、预处理对木质素吸附蛋白的影响规律及机制等研究。这对完善木质纤维素酶解机制、设法减轻预处理后木质素对酶解的不利影响、有针对性地复配纤维素酶系或进行菌株改造等具有重要参考价值。

将木质纤维素通过酶水解生成可发酵糖，进而发酵生产液体燃料和大宗化学品，对缓解人类社会目前面临化石资源短缺、环境污染等问题具有重要意义。但木质素对纤维素酶的非生产性吸附影响了纤维素酶解效率。预处理是提高纤维素酶解性能的重要步骤，但预处理过程中木质素的含量、结构和性质等将发生变化。至今为止，木质素对纤维素酶及其不同酶组分的吸附特征尚不清楚，预处理过程中木质素结构和性质的变化规律及预处理对木质素吸附纤维素酶的影响和机制尚未阐明。本项目针对上述问题，较为系统地开展不同预处理对纤维原料酶解性能的改善及其机制、预处理过程中木质素结构和性质变化规律、以及预处理对木质素吸附纤维素酶的影响及机制研究。结果表明：高温热水、稀硫酸、碱性预处理、酸性亚硫酸盐等不同方法预处理对不同纤维原料的酶解性能具有不同改善效果，这与预处理后原料在生物结构、化学组成、不同组成的结构和性质等方面发生的变化及其变化程度不同有关。针叶木、阔叶木、玉米秸秆和红麻等不同种类原料的木质素的结构和性质存在差异，对纤维素酶也表现出不同的吸附性能，研究表明木质素中的结构单元类型、酚羟基、羧酸、脂肪羟基等功能基类型和含量的差异，是造成不同原料木质素对纤维素酶具有不同吸附特征的可能原因。不同预处理过程中木质素的结构和性质发生不同的变化。木质素对纤维素酶的不同酶组分也表现出不同的吸附和抑制特征，其中木质素对CBH、木聚糖酶的影响大于对内切酶和葡萄糖苷酶的影响。与预处理前相比，预处理后木质素对纤维素酶的吸附能力和对不同酶活力的抑制作用增强，木质素与酶蛋白之间的疏水性作用和电荷作用或许是影响木素和纤维素酶吸附的主要因素。研究结果对完善木质纤维素酶解机制、设法根据具体情况有针对性地通过调整酶系等方法减轻木质素的不利影响、以及对菌株酶系进行改造等具有重要参考价值。