Crystal Structure of Glycoside Hydrolase Family 55 β-1,3-Glucanase from the Basidiomycete Phanerochaete chrysosporium
Crystal Structure of Glycoside Hydrolase Family 55 β-1,3-Glucanase from the Basidiomycete Phanerochaete chrysosporium
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DOI：
10.1074/jbc.m808122200
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发表时间：
2009-04-10
影响因子：
4.8
通讯作者：
Samejima, Masahiro
中科院分区：
文献类型：
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作者：
Ishida, Takuya;Fushinobu, Shinya;Samejima, Masahiro
糖苷水解酶家族55由主要来自丝状真菌的β-1，3-葡聚糖酶组成。来自担子菌类黄孢原毛平革菌的β-1，3-葡聚糖酶（Lam 55 A）以外切模式水解β-1，3-葡聚糖，同时转化异头构型，并从β-1，3/1，6-葡聚糖产生除葡萄糖之外的龙胆二糖。在这里，我们报告的晶体结构的Lam 55 A，建立三维结构的糖苷水解酶55的成员首次。Lam 55 A在单一多肽链中具有两个β-螺旋结构域。这两个结构域被长的连接区分开，但并排放置，整体结构类似于肋骨笼。在复合物中，一个右旋内酯分子结合在两个β-螺旋结构域之间的口袋底部。基于右旋内酯分子的位置，Glu-633似乎是催化酸，而催化碱残基无法鉴别。底物结合口袋似乎能够接受切割位点附近的龙胆二糖单位，并且根据该酶对各种β-1，3-葡聚糖寡糖的活性，从口袋中延伸出一条长裂缝。总之，我们提供了两个β-螺旋结构域的界面处的底物结合位点的重要特征，展示了意想不到的各种碳水化合物结合模式。
Glycoside hydrolase family 55 consists of beta-1,3-glucanases mainly from filamentous fungi. A beta-1,3-glucanase (Lam55A) from the Basidiomycete Phanerochaete chrysosporium hydrolyzes beta-1,3-glucans in the exo-mode with inversion of anomeric configuration and produces gentiobiose in addition to glucose from beta-1,3/1,6-glucans. Here we report the crystal structure of Lam55A, establishing the three-dimensional structure of a member of glycoside hydrolase 55 for the first time. Lam55A has two beta-helical domains in a single polypeptide chain. These two domains are separated by a long linker region but are positioned side by side, and the overall structure resembles a rib cage. In the complex, a gluconolactone molecule is bound at the bottom of a pocket between the two beta-helical domains. Based on the position of the gluconolactone molecule, Glu-633 appears to be the catalytic acid, whereas the catalytic base residue could not be identified. The substrate binding pocket appears to be able to accept a gentiobiose unit near the cleavage site, and a long cleft runs from the pocket, in accordance with the activity of this enzyme toward various beta-1,3-glucan oligosaccharides. In conclusion, we provide important features of the substrate-binding site at the interface of the two beta-helical domains, demonstrating an unexpected variety of carbohydrate binding modes.