Zhang Jian, Kang Lin, Shen Wei, Collings Cynthia, Gong Heng, Vander Meulen Kirk, Fox Brian G, Gilcher Elise, Dumesic James A, Ding Shi-You
School of Biotechnology, East China University of Science and Technology, 130 Meilong Road, Shanghai 200237, China.
Department of Plant Biology, Michigan State University, East Lansing, Michigan 48824, United States.
ACS Sustain Chem Eng. 2025 May 20;13(21):7781-7788. doi: 10.1021/acssuschemeng.5c00692. eCollection 2025 Jun 2.
The γ-valerolactone (GVL) pretreatment is one of the leading solvent-based methods for producing high-quality lignin under mild conditions. However, the glucan conversion yield from GVL pretreated biomass remains unsatisfactory. To explore the discrepancies between the relatively low glucan conversion and high lignin extraction, we conducted GVL-HCl and NaOH pretreatments on poplar and investigated their effects on lignin content and location, as well as on enzymatic hydrolysis of poplar cell walls at the subcellular level. Under designated pretreatment conditions of GVL-HCl (90% GVL, 0.1 M HCl, 100 °C, 1 h) and NaOH (1 M, 121 °C, 2 h), the glucan conversion yields were 69.4% and 95.8%, with lignin removal rates of 67.8% and 47.7%, respectively. Four types of GFP-labeled carbohydrate binding modules were used to identify different forms of cellulose in the pretreated cell walls. The overall binding intensities to pretreated poplar were stronger for NaOH compared to GVL-HCl pretreatment. Stimulated Raman scattering microscopy imaging revealed that GVL-HCl preferentially extracted lignin from the compound middle lamella and cell corner areas, while NaOH effectively dissolved lignin in the secondary cell walls. Real-time imaging of cellulase degradation of pretreated cell walls further indicated that digestion started from both the cell lumen and the compound middle lamella areas for GVL, whereas it occurred uniformly across the secondary cell walls for NaOH. Our findings suggest that the location of lignin removal during pretreatment is crucial for enzymatic cellulose degradation, in addition to the total amount of lignin extraction.
γ-戊内酯（GVL）预处理是在温和条件下生产高质量木质素的主要溶剂法之一。然而，GVL预处理生物质的葡聚糖转化率仍不尽人意。为了探究相对较低的葡聚糖转化率与高木质素提取率之间的差异，我们对杨树进行了GVL-HCl和NaOH预处理，并在亚细胞水平上研究了它们对木质素含量和位置以及杨树细胞壁酶解的影响。在GVL-HCl（90% GVL，0.1 M HCl，100 °C，1 h）和NaOH（1 M，121 °C，2 h）的指定预处理条件下，葡聚糖转化率分别为69.4%和95.8%，木质素去除率分别为67.8%和47.7%。使用四种类型的绿色荧光蛋白标记的碳水化合物结合模块来识别预处理细胞壁中不同形式的纤维素。与GVL-HCl预处理相比，NaOH对预处理杨树的总体结合强度更强。受激拉曼散射显微镜成像显示，GVL-HCl优先从复合中层和细胞角区域提取木质素，而NaOH有效地溶解了次生细胞壁中的木质素。预处理细胞壁纤维素酶降解的实时成像进一步表明，GVL处理时消化从细胞腔和复合中层区域开始，而NaOH处理时在次生细胞壁上均匀发生。我们的研究结果表明，除了木质素提取总量外，预处理过程中木质素去除的位置对纤维素酶降解至关重要。
