Structural and Functional Basis of Difructose Anhydride Ill Hydrolase, Which Sequentially Converts Inulin Using the Same Catalytic Residue
Structural and Functional Basis of Difructose Anhydride Ill Hydrolase, Which Sequentially Converts Inulin Using the Same Catalytic Residue
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二果糖酐 III 水解酶的结构和功能基础，该酶使用相同的催化残基依次转化菊粉
DOI：
10.1021/acscatal.8b02424
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发表时间：
2018
期刊：
影响因子：
12.9
通讯作者：
Mu Wanmeng
中科院分区：
文献类型：
--
作者：
Yu Shuhuai;Shen Hui;Cheng Yuanyuan;Zhu Yingying;Li Xu;Mu Wanmeng
果聚糖菊粉是由O-糖苷键连接的多聚果糖组成，多种酶参与其分解，为生物体提供能量。具体地，菊粉果糖转移酶（IFFT酶）将菊粉解聚为二果糖酐III（DFA-III）。DFA-III被DFA-III水解酶（DFA-IIIase）进一步降解。这项工作表明，DFA-Ⅲ酶的结构是一个三聚体，每个单体显示一个右手β-螺旋折叠，这类似于IFTase，除了一个额外的盖子覆盖活性中心。有了这个盖子，除了使用相同的位点和反应条件水解DFA-III之外，DFA-III酶还能够将菊粉转化为DFA-III（IFFT酶活性）。这种不寻常的和意想不到的顺序催化归因于在IFFT酶和DFA-Ⅲ酶的活性中心中的极其保守的残基和由盖子的打开和关闭调节的催化残基的质子化状态。本工作为进一步研究菊粉在自然界中的代谢奠定了基础，并提供了一个顺序酶催化的例子。
Fructan inulin is composed of polymeric fructoses linked by O-glycosidic bonds, and a variety of enzymes are involved in its decomposition to provide energy for organisms. Specifically, inulin fructotransferase (IFTase) depolymerizes inulin to difructose anhydride III (DFA-III). DFA-III was reported to be further degraded by DFA-III hydrolyase (DFA-IIIase). This work reveals that the structure of DFA-IIIase is a trimer, with each monomer displaying a right-handed β-helix fold, which resembles IFTase except for an extra lid covering the active center. With this lid, DFA-IIIase is capable of converting inulin to DFA-III (IFTase activity) in addition to hydrolyzing DFA-III using the same site and reaction conditions. This unusual and unexpected sequential catalysis is ascribed to the extremely conserved residues in the active center of IFTase and DFA-IIIase and the protonated states of the catalytic residue that are regulated by the opening and closing of the lid. This work paves the way for further investigation of the metabolism of inulin in nature and provides an example of sequential enzymatic catalysis.