The crystal structure of the catalytic core domain of endoglucanase I from Trichoderma reesei at 3.6 angstrom resolution, and a comparison with related enzymes
The crystal structure of the catalytic core domain of endoglucanase I from Trichoderma reesei at 3.6 angstrom resolution, and a comparison with related enzymes
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DOI：
10.1006/jmbi.1997.1243
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发表时间：
1997-09-26
影响因子：
5.6
通讯作者：
Jones, TA
中科院分区：
文献类型：
--
作者：
Kleywegt, GJ;Zou, JY;Jones, TA
纤维素是生物圈中最丰富的聚合物。虽然它一般耐降解，但它可以被纤维水解生物水解，这些生物已经进化出多种结构不同的酶，纤维生物水解酶和内切葡聚糖酶，为此内切葡聚糖酶I（EG I）是纤维水解真菌里氏木霉产生的主要内切葡聚糖酶，占该生物产生的纤维素酶总量的5 - 10%。与Humicola insolens的EG I和T. reesei的纤维素生物水解酶I （CBH I）一起，该酶被归类为糖基水解酶家族7，它催化水解具有净保留的端粒构型。采用分子替换法，以T. reesei CBH I和H. insolens EG I结构为搜索模型，在3.6埃分辨率下确定了T. reesei EG I的催化核心结构域（残基1 ~ 371）。尽管分辨率有限，但通过采用2倍非晶体对称（NCS），成功地改进了结构。最终模型的x因子为0.201（无r为0.258）。EG I的结构显示了一个延伸的、开放的底物结合裂缝，而不是在同源的纤维素生物水解酶CBH I中发现的一个隧道。这证实了先前的建议，CBH I中的隧道形成环在EG I中被删除，这导致EG I中有一个开放的活性位点，使其能够作为内切葡聚糖酶发挥作用。将EG I与几种相关酶的结构进行比较，揭示了其结构的相似性和与降解特定底物的生物学功能相关的差异。本文提出了一种可能的结构解释，解释了T. reesei和H. insolens EG . I的pH值差异。(C) 1997学术出版社有限公司
Cellulose is the most abundant polymer in the biosphere. Although generally resistant to degradation, it may be hydrolysed by cellulolytic organisms that have evolved a variety of structurally distinct enzymes, cellobiohydrolases and endoglucanases, for this purpose Endoglucanase I(EG I) is the major endoglucanase produced by the cellulolytic fungus Trichoderma reesei, accounting for 5 to 10% of the total amount of cellulases produced by this organism. Together with EG I from Humicola insolens and T. reesei cellobiohydrolase I (CBH I), the enzyme is classified into family 7 of the glycosyl hydrolases, and it catalyses hydrolysis with a net retention of the anomeric configuration.The structure of the catalytic core domain (residues 1 to 371) of EG I from T. reesei has been determined at 3.6 Angstrom resolution by the molecular replacement method using the structures of T. reesei CBH I and H. insolens EG I as search models. By employing the 2-fold non-crystallographic symmetry (NCS), the structure was refined successfully, despite the Limited resolution. The final model has an X-factor of 0.201 (R-free 0.258).The structure of EG I reveals an extended, open substrate-binding cleft, rather than a tunnel as found in the homologous cellobiohydrolase CBH I. This confirms the earlier proposal that the tunnel-forming loops in CBH I have been deleted in EG I, which has resulted in an open active site in EG I, enabling it to function as an endoglucanase. Comparison of the structure of EG I with several related enzymes reveals structural similarities, and differences that relate to their biological function in degrading particular substrates. A possible structural explanation of the drastically different pH profiles of T. reesei and H. insolens EG I is proposed. (C) 1997 Academic Press Limited.