Degradation of microcrystalline cellulose and non-pretreated plant biomass by a cell-free extracellular cellulase/hemicellulase system from the extreme thermophilic bacterium Caldicellulosiruptor bescii
Degradation of microcrystalline cellulose and non-pretreated plant biomass by a cell-free extracellular cellulase/hemicellulase system from the extreme thermophilic bacterium Caldicellulosiruptor bescii
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DOI：
10.1016/j.jbiosc.2012.07.019
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发表时间：
2013-01-01
影响因子：
2.8
通讯作者：
Yokoyama, Hiroshi
中科院分区：
文献类型：
--
作者：
Kanafusa-Shinkai, Sumiyo;Wakayama, Jun'ichi;Yokoyama, Hiroshi
热纤维素酶是一种纤维素分解/半纤维素分解厌氧菌，其胞外分泌多种蛋白质，包括具有两个催化结构域的多结构域纤维素酶，用于植物生物质降解。C.降解besophila细胞已经被很好地表征，但是C.但是，贝氏并没有得到很好的研究。在本研究中，C.从无细胞培养上清液中制备besartan CEC，并表征其对限定底物和未预处理的植物生物质的降解特性。由糖苷水解酶家族5、9、10、44和48组成的四种多结构域纤维素酶（Cbes_1857、Cbes_1859、Cbes_1865和Cbes_1867）是通过质谱法在CEC中鉴定的主要酶。CEC降解木聚糖、甘露糖基底物、β-1，4-连接葡聚糖（包括微晶纤维素（Avicel））以及未经预处理的梯牧草和稻草。然而，没有观察到几丁质、果胶、葡聚糖和小麦淀粉的降解。梯牧草和Avicel的最适降解温度为75 ℃，羧甲基纤维素的最适降解温度为85 ℃，木聚糖的最适降解温度>85 ℃。这些底物的最适pH为5-6。将降解活性与来自真菌里氏木霉（Trichoderma reesei）的CEC（用于植物生物质糖化的最常见的酶）进行比较。结果表明，C. besenchymal CEC比T.里氏木属C. besampleCEC可能归因于纤维素酶的双催化结构域结构。(C)2012年，生物技术学会，日本。All rights reserved.
Caldicellulosiruptor bescii is a cellulolytic/hemicellulolytic anaerobe, which extracellularly secretes various proteins, including multidomain cellulases with two-catalytic domains, for plant biomass degradation. Degradation by C. bescii cells has been well characterized, but degradation by the cell-free extracellular cellulase/hemicellulase system (CEC) of C. bescii has not been as well studied. In the present study, C. bescii CEC was prepared from cell-free culture supernatant, and the degradation properties for defined substrates and non-pretreated plant biomass were characterized. Four multidomain cellulases (Cbes_1857, Cbes_1859, Cbes_1865, and Cbes_1867), composed of the glycoside hydrolase families 5, 9, 10, 44, and 48, were the major enzymes identified in the CEC by mass spectrometry. The CEC degraded xylan, mannose-based substrates, beta-1,4-linked glucans, including microcrystalline cellulose (Avicel), and non-pretreated timothy grass and rice straw. However, degradation of chitin, pectin, dextran, and wheat starch was not observed. The optimum temperatures for degradation activities were 75 degrees C for timothy grass and Avicel, 85 degrees C for carboxylmethyl cellulose, and >85 degrees C for xylan. The optimum pH for these substrates was 5-6. The degradation activities were compared with a CEC derived from the fungus Trichoderma reesei, the most common enzyme used for plant biomass saccharification. The amounts of degraded Avicel, timothy grass, and rice straw by C. bescii CEC were 2.2-2.4-fold larger than those of T. reesei CEC. The high hydrolytic activity of C. bescii CEC might be attributed to the two-catalytic domain architecture of the cellulases. (C) 2012, The Society for Biotechnology, Japan. All rights reserved.