Lawrence C M, Rodwell V W, Stauffacher C V
Department of Biological Sciences, Purdue University, West Lafayette, IN 47907, USA.
Science. 1995 Jun 23;268(5218):1758-62. doi: 10.1126/science.7792601.
The rate-limiting step in cholesterol biosynthesis in mammals is catalyzed by 3-hydroxy-3-methylglutaryl-coenzyme A (HMG-CoA) reductase, a four-electron oxidoreductase that converts HMG-CoA to mevalonate. The crystal structure of HMG-CoA reductase from Pseudomonas mevalonii was determined at 3.0 angstrom resolution by multiple isomorphous replacement. The structure reveals a tightly bound dimer that brings together at the subunit interface the conserved residues implicated in substrate binding and catalysis. These dimers are packed about a threefold crystallographic axis, forming a hexamer with 23 point group symmetry. Difference Fourier studies reveal the binding sites for the substrates HMG-CoA and reduced or oxidized nicotinamide adenine dinucleotide [NAD(H)] and demonstrate that the active sites are at the dimer interfaces. The HMG-CoA is bound by a domain with an unusual fold, consisting of a central alpha helix surrounded by a triangular set of walls of beta sheets and alpha helices. The NAD(H) is bound by a domain characterized by an antiparallel beta structure that defines a class of dinucleotide-binding domains.
哺乳动物胆固醇生物合成中的限速步骤由3-羟基-3-甲基戊二酰辅酶A（HMG-CoA）还原酶催化，这是一种四电子氧化还原酶，可将HMG-CoA转化为甲羟戊酸。通过多同晶置换法，以3.0埃的分辨率确定了来自甲基营养型假单胞菌的HMG-CoA还原酶的晶体结构。该结构揭示了一个紧密结合的二聚体，它在亚基界面处汇集了与底物结合和催化作用相关的保守残基。这些二聚体围绕着一个三重晶体学轴堆积，形成具有23点群对称性的六聚体。差值傅里叶研究揭示了底物HMG-CoA和还原型或氧化型烟酰胺腺嘌呤二核苷酸[NAD(H)]的结合位点，并证明活性位点位于二聚体界面处。HMG-CoA由一个具有不寻常折叠的结构域结合，该结构域由一个中央α螺旋组成，周围是一组由β片层和α螺旋构成的三角形壁。NAD(H)由一个以反平行β结构为特征的结构域结合，该结构域定义了一类二核苷酸结合结构域。
