Tropinone synthesis via an atypical polyketide synthase and P450-mediated cyclization
Tropinone synthesis via an atypical polyketide synthase and P450-mediated cyclization
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DOI：
10.1038/s41467-018-07671-3
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发表时间：
2018-12-11
影响因子：
16.6
通讯作者：
Barry, Cornelius S.
中科院分区：
文献类型：
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作者：
Bedewitz, Matthew A.;Jones, A. Daniel;Barry, Cornelius S.
托品酮是生物合成具有8-氮杂双环[3.2.1]辛烷核心双环结构的非常重要的托品烷生物碱的第一中间体，其定义了该生物碱类别。托品酮的化学合成于1901年实现，但托品酮生物合成的机制仍然难以捉摸。在这项研究中，我们确定了根表达的III型聚酮合酶颠茄（AbPYKS），催化形成4-（1-甲基-2-吡咯烷基）-3-氧代丁酸。这种催化通过非典型机制进行，该机制直接利用未缀合的N-甲基-Δ（1）-吡咯啉鎓阳离子作为两轮丙二酰辅酶A介导的脱羧缩合的起始底物。随后由4-（1-甲基-2-吡咯烷基）-3-氧代丁酸形成托品酮通过细胞色素P450介导的AbCYP 82 M3催化实现。AbPYKS和AbCYP 82 M3的沉默降低了A.颠茄本研究揭示了托品酮生物合成的机理，解释了植物中吡咯烷和托品烷的共存，并证明了在不产托品烷的植物中进行托品烷工程的可行性。
Tropinone is the first intermediate in the biosynthesis of the pharmacologically important tropane alkaloids that possesses the 8-azabicyclo[3.2.1] octane core bicyclic structure that defines this alkaloid class. Chemical synthesis of tropinone was achieved in 1901 but the mechanism of tropinone biosynthesis has remained elusive. In this study, we identify a root-expressed type III polyketide synthase from Atropa belladonna (AbPYKS) that catalyzes the formation of 4-(1-methyl-2-pyrrolidinyl)-3-oxobutanoic acid. This catalysis proceeds through a non-canonical mechanism that directly utilizes an unconjugated N-methyl-Delta(1)-pyrrolinium cation as the starter substrate for two rounds of malonyl-Coenzyme A mediated decarboxylative condensation. Subsequent formation of tropinone from 4-(1-methyl-2-pyrrolidinyl)-3-oxobutanoic acid is achieved through cytochrome P450-mediated catalysis by AbCYP82M3. Silencing of AbPYKS and AbCYP82M3 reduces tropane levels in A. belladonna. This study reveals the mechanism of tropinone biosynthesis, explains the in planta co-occurrence of pyrrolidines and tropanes, and demonstrates the feasibility of tropane engineering in a non-tropane producing plant.