纤维素酶在纺织、造纸、新能源等领域具有广阔应用前景。现有纤维素酶多来自真菌，普遍存在碱性条件酶活低、不耐高温、生产成本较高等缺点。而细菌纤维素酶很好地弥补了真菌纤维素酶的上述缺点，因此对它的研究已成为纤维素酶研究中的一个热点。为从极端环境中的未培养微生物中寻找新型纤维素酶，本研究拟从中国最热地区-新疆火焰山的土壤样品中建立宏基因组文库，并筛库获得热稳定、高活性的细菌纤维素酶。然后联合应用易错PCR和DNA改组技术确定与酶的热稳定性相关的关键位点，并利用X-射线晶体衍射技术解析野生酶和突变酶的三维结构。最后，通过分析突变位点在蛋白质三维结构图上的分布和位置效应、突变位点的疏水效应、以及突变位点对氢键、二硫键和离子对形成的影响，阐明细菌纤维素酶热稳定的结构特征和分子机制。本研究为探索纤维素酶的热稳定机制以及开发极端环境中的纤维素酶资源提供了新的方法和思路，具有重要的理论意义和应用潜力。

Cellulases are relatively costly enzymes, and have wide industrial applictions in many field, such as textile, paper making, and bioenergy. Currently, most commercial celluases are of fungal origin (Trichoderma species and Aspergillus species), and these enzymes have some universal drawbacks, including low activity in alkaline condition, sensitive to high temperature, and high production cost. Recently, bacterial cellulases have become a hotspot of cellulase research due to its tolerance to high temperature, neutral or alkaline pH optimum, and low production cost. To find novel cellulases from unculturable microorganisms in extreme environment, metagenomic libraries will be constructed in this study using soil samples from the Flame Mountain of Xinjiang province-the hottest place in China. Library screening will be performed subsequently to obtain bacterial cellulase with thermostability and high-activity, followed by error-prone PCR and DNA shuffling to discover the key sites underlying thermostability of the cellulase. Then, x-ray diffraction technology will be used to analyze the three-dimensional structures of wild-type and mutated enzyme. Finally, the structural features and molecular mechanisms related to thermostablility of bacterial cellulases will be elucidated by analyzing the distribution and location effect as well as the hydrophobic effect of mutation sites, and effects of mutation sites on the form of hydrogen bonding, disulfide bonding, and ion pairing.This study will provide a new method and insight for studying thermostable mechanism of cellulases and exploiting cellulase resources from extreme environments, and thus has theoretical significance and tremendous application potential.