Chu Yindi, Hao Zhenzhen, Wang Kaikai, Tu Tao, Huang Huoqing, Wang Yuan, Bai Ying Guo, Wang Yaru, Luo Huiying, Yao Bin, Su Xiaoyun
1Key Laboratory for Feed Biotechnology of the Ministry of Agriculture, Feed Research Institute, Chinese Academy of Agricultural Sciences, No. 12 South Zhongguancun Street, Beijing, 100081 China.
2Department of Microbiology and Parasitology, Institute of Basic Medical Sciences, Chinese Academy of Medical Sciences and Peking Union Medical College, 5# Dong Dan San Tiao, Beijing, 100005 China.
Biotechnol Biofuels. 2019 Dec 3;12:279. doi: 10.1186/s13068-019-1617-2. eCollection 2019.
Regarding plant cell wall polysaccharides degradation, multimodular glycoside hydrolases (GHs) with two catalytic domains separated by one or multiple carbohydrate-binding domains are rare in nature. This special mode of domain organization endows the CelA (GH9-CBM3c-CBM3b-CBM3b-GH48) remarkably high efficiency in hydrolyzing cellulose. Xyn10C/Cel48B from the same bacterium is also such an enzyme which has, however, evolved to target both xylan and cellulose. Intriguingly, the GH10 endoxylanase and GH48 cellobiohydrolase domains are both dual functional, raising the question if they can act synergistically in hydrolyzing cellulose and xylan, the two major components of plant cell wall.
In this study, we discovered that Xyn10C and Cel48B, which stood for the N- and C-terminal catalytic domains, respectively, cooperatively released much more cellobiose and cellotriose from cellulose. In addition, they displayed intramolecular synergy but only at the early stage of xylan hydrolysis by generating higher amounts of xylooligosaccharides including xylotriose, xylotetraose, and xylobiose. When complex lignocellulose corn straw was used as the substrate, the synergy was found only for cellulose but not xylan hydrolysis.
This is the first report to reveal the synergy between a GH10 and a GH48 domain. The synergy discovered in this study is helpful for understanding how captures energy from these recalcitrant plant cell wall polysaccharides. The insight also sheds light on designing robust and multi-functional enzymes for plant cell wall polysaccharides degradation.
关于植物细胞壁多糖的降解，具有两个催化结构域且由一个或多个碳水化合物结合结构域分隔的多模块糖苷水解酶（GHs）在自然界中很罕见。这种特殊的结构域组织模式赋予了CelA（GH9 - CBM3c - CBM3b - CBM3b - GH48）极高的纤维素水解效率。来自同一细菌的Xyn10C/Cel48B也是这样一种酶，然而，它已进化为靶向木聚糖和纤维素。有趣的是，GH10内切木聚糖酶和GH48纤维二糖水解酶结构域都是双功能的，这就提出了一个问题，即它们在水解植物细胞壁的两种主要成分纤维素和木聚糖时是否能协同作用。
在本研究中，我们发现分别代表N端和C端催化结构域的Xyn10C和Cel48B能协同从纤维素中释放出更多的纤维二糖和纤维三糖。此外，它们表现出分子内协同作用，但仅在木聚糖水解的早期阶段通过产生更多的木寡糖（包括木三糖、木四糖和木二糖）来实现。当使用复杂的木质纤维素玉米秸秆作为底物时，仅在纤维素水解中发现了协同作用，而在木聚糖水解中未发现。
这是第一份揭示GH10和GH48结构域之间协同作用的报告。本研究中发现的协同作用有助于理解[此处原文缺失相关内容]如何从这些顽固的植物细胞壁多糖中获取能量。这一见解也为设计用于植物细胞壁多糖降解的强大且多功能的酶提供了思路。
