中国科学院上海有机化学研究所潘李锋团队报道了一种催化2+2和4+2环加成的环化酶。相关研究成果于2023年1月23日发表在《自然—化学》。

环加成反应是化学合成中应用最广泛的反应之一。自然界通过多种酶实现了这些环化反应，包括催化协同4+2环加成的Diels–Alderases，但具有2+2环化酶活性的生物合成酶尚未被发现。

该文中，研究人员报道了一种与外显选择性4+2环化酶同源的β-桶折叠蛋白，PloI4，其在吡喃霉素生物合成中起作用，催化竞争性的2+2和4+2环加成反应。PloI4被认为在吡咯孢子蛋白A的生物合成中催化内4+2环加成；然而，当用PloI4处理pyroindomycins的底物前体时，除了外-和内4+2加合物外，还产生了外2+2加合。生化表征、计算分析、（共）晶体结构和诱变结果验证了PloI4的催化多功能性。机制研究包括将PloI4定向工程至优先产生外4+2、内4+2或外2+2产物的变体。

该项工作阐明了酶热2+2环加成，并提供了一个酶与其底物一起进化，以实现专门化和活性提高的过程的证据。

附：英文原文

Title: A cyclase that catalyses competing 2 + 2 and 4 + 2 cycloadditions

Author: Wang, Hongbo, Zou, Yike, Li, Miao, Tang, Zhijun, Wang, Jiabao, Tian, Zhenhua, Strassner, Nina, Yang, Qian, Zheng, Qingfei, Guo, Yujiao, Liu, Wen, Pan, Lifeng, Houk, K. N.

Issue&Volume: 2023-01-23

Abstract: Cycloaddition reactions are among the most widely used reactions in chemical synthesis. Nature achieves these cyclization reactions with a variety of enzymes, including Diels–Alderases that catalyse concerted 4+2 cycloadditions, but biosynthetic enzymes with 2+2 cyclase activity have yet to be discovered. Here we report that PloI4, a β-barrel-fold protein homologous to the exo-selective 4+2 cyclase that functions in the biosynthesis of pyrroindomycins, catalyses competitive 2+2 and 4+2 cycloaddition reactions. PloI4 is believed to catalyse an endo-4+2 cycloaddition in the biosynthesis of pyrrolosporin A; however, when the substrate precursor of pyrroindomycins was treated with PloI4, an exo-2+2 adduct was produced in addition to the exo- and endo-4+2 adducts. Biochemical characterizations, computational analyses, (co)crystal structures and mutagenesis outcomes have allowed the catalytic versatility of PloI4 to be rationalized. Mechanistic studies involved the directed engineering of PloI4 to variants that produced the exo-4+2, endo-4+2 or exo-2+2 product preferentially. This work illustrates an enzymatic thermal 2+2 cycloaddition and provides evidence of a process through which an enzyme evolves along with its substrate for specialization and activity improvement.

DOI: 10.1038/s41557-022-01104-x

Source: https://www.nature.com/articles/s41557-022-01104-x