Crystal structures of enoyl-coenzyme A (CoA) isomerase from Bosea sp. PAMC 26642 (BoECI) and enoyl-CoA hydratase from Hymenobacter sp. PAMC 26628 (HyECH) were determined at 2.35 and 2.70 Å resolution, respectively. BoECI and HyECH are members of the crotonase superfamily and are enzymes known to be involved in fatty acid degradation. Structurally, these enzymes are highly similar except for the orientation of their C-terminal helix domain. Analytical ultracentrifugation was performed to determine the oligomerization states of BoECI and HyECH revealing they exist as trimers in solution. However, their putative ligand-binding sites and active site residue compositions are dissimilar. Comparative sequence and structural analysis revealed that the active site of BoECI had one glutamate residue (Glu135), this site is occupied by an aspartate in some ECIs, and the active sites of HyECH had two highly conserved glutamate residues (Glu118 and Glu138). Moreover, HyECH possesses a salt bridge interaction between Glu98 and Arg152 near the active site. This interaction may allow the catalytic Glu118 residue to have a specific conformation for the ECH enzyme reaction. This salt bridge interaction is highly conserved in known bacterial ECH structures and ECI enzymes do not have this type of interaction. Collectively, our comparative sequential and structural studies have provided useful information to distinguish and classify two similar bacterial crotonase superfamily enzymes.

中文翻译：

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细菌烯酰辅酶A异构酶和烯酰辅酶A水合酶的结构和序列比较。

Bosea sp。的烯酰辅酶A（CoA）异构酶的晶体结构。PAMC 26642（博ECI）和烯酰辅酶A水合酶从Hymenobacter SP。PAMC 26628（Hy ECH）分别以2.35和2.70Å的分辨率测定。Bo ECI和Hy ECH是巴豆酶超家族的成员，并且是已知与脂肪酸降解有关的酶。在结构上，这些酶除其C末端螺旋结构域的方向外，非常相似。进行分析超速离心以确定Bo ECI和Hy的低聚状态ECH显示它们以三聚体形式存在于溶液中。但是，其推定的配体结合位点和活性位点残基组成不同。比较序列和结构分析表明，Bo ECI的活性位点具有一个谷氨酸残基（Glu135），在某些ECI中该位点被天冬氨酸占据，Hy ECH的活性位点具有两个高度保守的谷氨酸残基（Glu118和Glu138）。 。而且，HyECH在活性位点附近的Glu98和Arg152之间具有盐桥相互作用。该相互作用可以使催化的Glu118残基具有对于ECH酶反应的特定构象。这种盐桥相互作用在已知的细菌ECH结构中高度保守，ECI酶不具有这种相互作用。总的来说，我们的比较性顺序和结构研究提供了有用的信息，以区分和分类两种相似的细菌巴豆酶超家族酶。