Department of Chemistry and Biochemistry, University of California , Los Angeles, California 90095, United States.
Department of Chemistry, University of California , Berkeley, California 94720, United States.
J Am Chem Soc. 2017 Aug 30;139(34):12060-12068. doi: 10.1021/jacs.7b06773. Epub 2017 Aug 21.
Malbrancheamide is a dichlorinated fungal indole alkaloid isolated from both Malbranchea aurantiaca and Malbranchea graminicola that belongs to a family of natural products containing a characteristic bicyclo[2.2.2]diazaoctane core. The introduction of chlorine atoms on the indole ring of malbrancheamide differentiates it from other members of this family and contributes significantly to its biological activity. In this study, we characterized the two flavin-dependent halogenases involved in the late-stage halogenation of malbrancheamide in two different fungal strains. MalA and MalA' catalyze the iterative dichlorination and monobromination of the free substrate premalbrancheamide as the final steps in the malbrancheamide biosynthetic pathway. Two unnatural bromo-chloro-malbrancheamide analogues were generated through MalA-mediated chemoenzymatic synthesis. Structural analysis and computational studies of MalA' in complex with three substrates revealed that the enzyme represents a new class of zinc-binding flavin-dependent halogenases and provides new insights into a potentially unique reaction mechanism.
马布兰奇酰胺是一种从马布兰切亚橙和马布兰切亚草中分离出来的二氯真菌吲哚生物碱，属于含有特征双环[2.2.2]二氮杂辛烷核心的天然产物家族。马布兰奇酰胺吲哚环上氯原子的引入使其有别于该家族的其他成员，并对其生物活性有重要贡献。在这项研究中，我们对两种不同真菌菌株中马布兰奇酰胺晚期卤化过程中涉及的两个黄素依赖卤化酶进行了表征。MalA 和 MalA' 催化游离前马布兰奇酰胺的迭代二氯化和单溴化，作为马布兰奇酰胺生物合成途径的最后步骤。通过 MalA 介导的化学酶合成生成了两种非天然的溴氯马布兰奇酰胺类似物。与三种底物结合的 MalA' 的结构分析和计算研究表明，该酶代表了一类新的锌结合黄素依赖卤化酶，并为潜在独特的反应机制提供了新的见解。
