Fatty‐acid degradation is an oxidative process that involves four enzymatic steps and is referred to as the β‐oxidation pathway. During this process, long‐chain acyl‐CoAs are broken down into acetyl‐CoA, which enters the mitochondrial tricarboxylic acid (TCA) cycle, resulting in the production of energy in the form of ATP. Enoyl‐CoA hydratase (ECH) catalyzes the second step of the β‐oxidation pathway by the syn addition of water to the double bond between C2 and C3 of a 2‐trans‐enoyl‐CoA, resulting in the formation of a 3‐hydroxyacyl CoA. Here, the crystal structure of ECH from Thermus thermophilus HB8 (TtECH) is reported at 2.85 Å resolution. TtECH forms a hexamer as a dimer of trimers, and wide clefts are uniquely formed between the two trimers. Although the overall structure of TtECH is similar to that of a hexameric ECH from Rattus norvegicus (RnECH), there is a significant shift in the positions of the helices and loops around the active‐site region, which includes the replacement of a longer α3 helix with a shorter α‐helix and 3₁₀‐helix in RnECH. Additionally, one of the catalytic residues of RnECH, Glu144 (numbering based on the RnECH enzyme), is replaced by a glycine in TtECH, while the other catalytic residue Glu164, as well as Ala98 and Gly141 that stabilize the enolate intermediate, is conserved. Their putative ligand‐binding sites and active‐site residue compositions are dissimilar.

中文翻译：

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嗜热栖热菌HB8烯酰辅酶A水合酶的晶体结构

脂肪酸降解是一个氧化过程，涉及四个酶促步骤，被称为β-氧化途径。在这个过程中，长链酰基辅酶A被分解成乙酰辅酶A，进入线粒体三羧酸（TCA）循环，从而以ATP的形式产生能量。烯酰辅酶 A 水合酶 (ECH) 催化 β 氧化途径的第二步，通过将水顺式加成到 2-反式-烯酰辅酶 A的 C2 和 C3 之间的双键上，从而形成 3-羟酰基辅酶A。在这里，来自Thermus thermophilus HB8 ( Tt ECH) 的 ECH 晶体结构以 2.85 Å 的分辨率报告。时间ECH作为三聚体的二聚体形成六聚体，并且在两个三聚体之间形成独特的宽裂隙。尽管Tt ECH的整体结构与来自褐家鼠( Rn ECH) 的六聚体 ECH 的结构相似，但活性位点区域周围的螺旋和环的位置发生了显着变化，其中包括替换了更长的 ECH。Rn ECH中具有较短 α 螺旋和 3_{个 10}螺旋的α3 螺旋。此外， Rn ECH的催化残基之一Glu144（编号基于Rn ECH 酶）在Tt中被甘氨酸取代ECH，而其他催化残基 Glu164 以及稳定烯醇中间体的 Ala98 和 Gly141 是保守的。它们推定的配体结合位点和活性位点残基组成不同。