Rafferty J B, Simon J W, Baldock C, Artymiuk P J, Baker P J, Stuitje A R, Slabas A R, Rice D W
Krebs Institute for Biomolecular Research, Department of Molecular Biology and Biotechnology, University of Sheffield, UK.
Structure. 1995 Sep 15;3(9):927-38. doi: 10.1016/S0969-2126(01)00227-1.
Enoyl acyl carrier protein reductase (ENR) catalyzes the NAD(P)H-dependent reduction of trans-delta 2-enoyl acyl carrier protein, an essential step in de novo fatty acid biosynthesis. Plants contain both NADH-dependent and separate NADPH-dependent ENR enzymes which form part of the dissociable type II fatty acid synthetase. Highly elevated levels of the NADH-dependent enzyme are found during lipid deposition in maturing seeds of oilseed rape (Brassica napus).
The crystal structure of an ENR-NAD binary complex has been determined at 1.9 A resolution and consists of a homotetramer in which each subunit forms a single domain comprising a seven-stranded parallel beta sheet flanked by seven alpha helices. The subunit has a topology highly reminiscent of a dinucleotide-binding fold. The active site has been located by difference Fourier analysis of data from crystals equilibrated in NADH.
The structure of ENR shows a striking similarity with the epimerases and short-chain alcohol dehydrogenases, in particular, 3 alpha,20 beta-hydroxysteroid dehydrogenase (HSD). The similarity with HSD extends to the conservation of a catalytically important lysine that stabilizes the transition state and to the use of a tyrosine as a base--with subtle modifications arising from differing requirements of the reduction chemistry.
烯酰酰基载体蛋白还原酶（ENR）催化依赖于NAD(P)H的反式δ2-烯酰酰基载体蛋白的还原反应，这是从头脂肪酸生物合成中的关键步骤。植物含有依赖NADH的ENR酶和独立的依赖NADPH的ENR酶，它们是可解离的II型脂肪酸合成酶的一部分。在油菜（甘蓝型油菜）成熟种子的脂质沉积过程中，发现依赖NADH的酶水平大幅升高。
已确定ENR-NAD二元复合物的晶体结构，分辨率为1.9 Å，由同四聚体组成，其中每个亚基形成一个单结构域，包含一个由七个α螺旋侧翼的七股平行β折叠。该亚基的拓扑结构与二核苷酸结合折叠高度相似。通过对在NADH中平衡的晶体数据进行差值傅里叶分析确定了活性位点。
ENR的结构与差向异构酶和短链醇脱氢酶有显著相似性，特别是3α,20β-羟基类固醇脱氢酶（HSD）。与HSD的相似性延伸到稳定过渡态的催化重要赖氨酸的保守性，以及酪氨酸作为碱基的使用——由于还原化学的不同要求而产生细微差异。
