Recombinant squalene synthase. A mechanism for the rearrangement of presqualene diphosphate to squalene
Recombinant squalene synthase. A mechanism for the rearrangement of presqualene diphosphate to squalene
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DOI：
10.1021/ja020411a
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发表时间：
2002-07-31
影响因子：
15
通讯作者：
Poulter, CD
中科院分区：
文献类型：
--
作者：
Blagg, BSJ;Jarstfer, MB;Poulter, CD
角鲨烯合酶（SQase）催化两个分子的法尼基二磷酸（FPP）缩合形成前角鲨烯二磷酸（PSPP），以及随后的重排和NADPH依赖性的PSPP还原成角鲨烯（SQ）。这些反应是胆固醇生物合成的第一个关键步骤。当重组SQase与FPP在二氢NADPH（NADPH（3），烟酰胺环中缺少5，6-双键的非反应性类似物）存在下温育时，形成三种产物：脱氢角鲨烯（DSQ），八氢番茄红素的C-30类似物;和rillingol（ROH），一种环丙基原醇，通过将水加成到叔环丙基原醇阳离子上形成，以前提出作为PSPP重排成SO的中间体（Poulter，C. D. 1990，23，70-77）。通过两条独立的合成路线，确定了叔环丙基甲醇的结构和绝对立体化学。从酶催化反应中分离ROH为角鲨烯生物合成中的环丙基原基-环丙基原基重排提供了强有力的证据。通过比较SQase催化的溶剂分解的PSPP在NADPH 3的存在下的情况下，在NADPH 3的存在下的反应，很明显，辅因子类似物的结合大大提高SQase控制的区域和立体化学的PSPP的重排的能力。
Squalene synthase (SQase) catalyzes the condensation of two molecules of farnesyl diphosphate (FPP) to form presqualene diphosphate (PSPP) and the subsequent rearrangement and NADPH-dependent reduction of PSPP to squalene (SQ). These reactions are the first committed steps in cholesterol biosynthesis. When recombinant SQase was incubated with FPP in the presence of dihydroNADPH (NADPH(3), an unreactive analogue lacking the 5,6-double bond in the nicotinamide ring), three products were formed: dehydrosqualene (DSQ), a C-30 analogue of phytoene; 10(S)-hydroxysqualene (HSQ), a hydroxy analogue of squalene; and rillingol (ROH), a cyclopropylcarbinyl alcohol formed by addition of water to the tertiary cyclopropylcarbinyl cation previously proposed as an intermediate in the rearrangement of PSPP to SO (Poulter, C. D. Acc. Chem. Res. 1990, 23, 70-77). The structure and absolute stereochemistry of the tertiary cyclopropylcarbinyl alcohol were established by synthesis using two independent routes. Isolation of ROH from the enzyme-catalyzed reaction provides strong evidence for a cyclopropylcarbinyl-cyclopropylcarbinyl rearrangement in the biosynthesis of squalene. By comparing the SQase-catalyzed solvolysis of PSPP in the absence of NADPH3 to the reaction in the presence of NADPH3, it is apparent that the binding of the cofactor analogue substantially enhances the ability of SQase to control the regio- and stereochemistry of the rearrangements of PSPP.