Evolution of an enzyme active site: The structure of a new crystal form of muconate lactonizing enzyme compared with mandelate racemase and enolase
Evolution of an enzyme active site: The structure of a new crystal form of muconate lactonizing enzyme compared with mandelate racemase and enolase
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DOI：
10.1073/pnas.95.18.10396
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发表时间：
1998-09-01
影响因子：
11.1
通讯作者：
Ringe, D
中科院分区：
文献类型：
--
作者：
Hasson, MS;Schlichting, I;Ringe, D
粘康酸内酯化酶（MLE）是恶臭假单胞菌的β-酮己二酸途径的组分，是在不同的总体反应的背景下催化羧酸的α-质子的提取的相关酶家族（“烯醇化酶超家族”）的成员。获得了MLE的新的非孪晶晶形式，其中一种衍射分辨率优于2.0埃。八聚体酶在这种晶体形式中的包装是不寻常的，因为不对称单元包含三个亚基。这里呈现的MLE结构不含结合的金属离子，但与最近确定的Mn 2+结合结构非常相似。因此，不存在金属离子不会扰乱活性位点的结构。烯醇化酶、扁桃酸消旋酶和MLE的结构重叠。金属配体的比较表明烯醇化酶可能保留了该酶家族祖先的一些特征。与其他参与催化的残基的比较表明了两种不寻常的保守模式：（i）催化原子的位置保持不变，尽管包含它们的残基位于蛋白质折叠的不同点;（ii）蛋白质支架中催化残基的位置是保守的，而它们的身份和催化作用各不相同。
Muconate lactonizing enzyme (MLE), a component of the beta-ketoadipate pathway of Pseudomonas putida, is a member of a family of related enzymes (the "enolase superfamily") that catalyze the abstraction of the alpha-proton of a carboxylic acid in the context of different overall reactions. New untwinned crystal forms of MLE were obtained, one of which diffracts to better than 2.0- Angstrom resolution. The packing of the octameric enzyme in this crystal form is unusual, because the asymmetric unit contains three subunits, The structure of MLE presented here contains no bound metal ion, but is very similar to a recently determined Mn2+-bound structure. Thus, absence of the metal ion does not perturb the structure of the active site. The structures of enolase, mandelate racemase, and MLE were superimposed. A comparison of metal ligands suggests that enolase may retain some characteristics of the ancestor of this enzyme family. Comparison of other residues involved in catalysis indicates two unusual patterns of conservation: (i) that the position of catalytic atoms remains constant, although the residues that contain them are located at different points in the protein fold; and (ii) that the positions of catalytic residues in the protein scaffold are conserved, whereas their identities and roles in catalysis vary.