CSIR-Institute Of Microbial Technology, Council Of Scientific and Industrial Research (CSIR), Sector 39 A, Chandigarh 160036, India.
Sci Rep. 2016 Dec 23;6:39634. doi: 10.1038/srep39634.
Cellulase catalyzes the hydrolysis of β-1,4-linkages of cellulose to produce industrially relevant monomeric subunits. Cellulases find their applications in pulp and paper, laundry, food and feed, textile, brewing industry and in biofuel production. These industries always have great demand for cellulases that can work efficiently even in harsh conditions such as high salt, heat, and acidic environments. While, cellulases with high thermal and acidic stability are already in use, existence of a high halotolerant cellulase is still elusive. Here, we report a novel cellulase Cel5R, obtained from soil metagenome that shows high halotolerance and thermal stability. The biochemical and functional characterization of Cel5R revealed its endoglucanase activity and high halostability. In addition, the crystal structure of Cel5R determined at 2.2 Å resolution reveals a large number of acidic residues on the surface of the protein that contribute to the halophilic nature of this enzyme. Moreover, we demonstrate that the four free and non-conserved cysteine residues (C65, C90, C231 and C273) contributes to the thermal stability of Cel5R by alanine scanning experiments. Thus, the newly identified endoglucanase Cel5R is a promising candidate for various industrial applications.
纤维素酶催化纤维素β-1,4-糖苷键的水解，产生具有工业应用价值的单体亚基。纤维素酶在制浆造纸、洗涤、食品和饲料、纺织、酿造工业以及生物燃料生产中都有应用。这些行业一直对能够在高盐、高温和酸性环境等苛刻条件下高效工作的纤维素酶有很大的需求。虽然已经有具有高热稳定性和高酸性稳定性的纤维素酶在使用，但仍缺乏高耐盐性的纤维素酶。在这里，我们报道了一种新型的纤维素酶 Cel5R，它来自土壤宏基因组，具有高耐盐性和热稳定性。对 Cel5R 的生化和功能特性的研究表明它具有内切葡聚糖酶活性和高耐盐性。此外，Cel5R 的晶体结构在 2.2Å分辨率下确定，揭示了该酶表面存在大量酸性残基，这有助于其嗜盐特性。此外，我们通过丙氨酸扫描实验证明，四个游离且非保守的半胱氨酸残基（C65、C90、C231 和 C273）对 Cel5R 的热稳定性有贡献。因此，新鉴定的内切葡聚糖酶 Cel5R 是各种工业应用的有前途的候选者。
