The crystal structure of endoglucanase CelA, a family 8 glycosyl hydrolase from Clostridium thermocellum
The crystal structure of endoglucanase CelA, a family 8 glycosyl hydrolase from Clostridium thermocellum
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DOI：
10.1016/s0969-2126(96)00031-7
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发表时间：
1996-03-15
期刊：
影响因子：
5.7
通讯作者：
Dominguez, R
中科院分区：
文献类型：
--
作者：
Alzari, PM;Souchon, H;Dominguez, R
背景：纤维素酶催化纤维素中糖苷键的水解，可分为几个不同的蛋白质家族。葡聚糖内切酶CELA是糖基水解酶家族8的成员之一，该家族的结构信息尚不清楚。结果：CELA的晶体结构是通过多次同象置换确定的，并被细化到1.65埃分辨率。蛋白质折叠成一个规则的(阿尔法/阿尔法)(6)桶，由六个内部和六个外部阿尔法螺旋组成。低聚纤维糖与至少5个D-葡萄糖基结合亚基(A-E)的酸性裂隙结合，使得剪切的糖苷键位于C和D亚基之间。位于底物结合灵巧中心的严格保守的残基Glu95被指定为质子供体的催化作用。结论：本分析为模拟同源家族8纤维素酶提供了基础。活性部位裂解的结构存在至少五个葡萄糖结合亚基，这解释了为什么家族8纤维素酶裂解至少五个D-葡萄糖亚单位的纤维素-低聚糖聚合物。此外，CELA的结构允许与序列上不相关的(α/α)(6)桶糖苷酶进行比较，这表明不同的糖基水解酶家族之间可能存在进化关系。
Background: Cellulases, which catalyze the hydrolysis of glycosidic bonds in cellulose, can be classified into several different protein families. Endoglucanase CelA is a member of glycosyl hydrolase family 8, a family for which no structural information was previously available.Results: The crystal structure of CelA was determined by multiple isomorphous replacement and refined to 1.65 Angstrom resolution. The protein folds into a regular (alpha/alpha)(6) barrel formed by six inner and six outer alpha helices. Cello-oligosaccharides bind to an acidic cleft containing at least five D-glucosyl-binding subsites (A-E) such that the scissile glycosidic linkage lies between subsites C and D. The strictly conserved residue Glu95, which occupies the center of the substrate-binding deft and is hydrogen bonded to the glycosidic oxygen, has been assigned the catalytic role of proton donor.Conclusions: The present analysis provides a basis for modeling homologous family 8 cellulases. The architecture of the active-site cleft, presenting at least five glucosyl-binding subsites, explains why family 8 cellulases cleave cello-oligosaccharide polymers that are at least five D-glucosyl subunits long. Furthermore, the structure of CelA allows comparison with (alpha/alpha)(6) barrel glycosidases that are not related in sequence, suggesting a possible, albeit distant, evolutionary relationship between different families of glycosyl hydrolases.