Schramma Kelsey R, Forneris Clarissa C, Caruso Alessio, Seyedsayamdost Mohammad R
Department of Chemistry, Princeton University , Princeton, New Jersey 08544, United States.
Department of Molecular Biology, Princeton University , Princeton, New Jersey 08544, United States.
Biochemistry. 2018 Jan 30;57(4):461-468. doi: 10.1021/acs.biochem.7b01147. Epub 2018 Jan 23.
Streptide is a ribosomally synthesized and post-translationally modified peptide with a unique cyclization motif consisting of an intramolecular lysine-tryptophan cross-link. Three radical S-adenosylmethionine enzymes, StrB, AgaB, and SuiB from different species of Streptococcus, have been shown to install this modification onto their respective precursor peptides in a leader-dependent fashion. Herein, we conduct detailed investigations to differentiate among several plausible mechanistic proposals, specifically addressing radical versus electrophilic addition to the indole during cross-link formation, the role of substrate side chains in binding in the enzyme active site, and the identity of the catalytic base in the reaction cycle. Our results are consistent with a radical electrophilic aromatic substitution mechanism for the key carbon-carbon bond-forming step. They also elaborate on other mechanistic features that underpin this unique and synthetically challenging post-translational modification.
链霉肽是一种核糖体合成且经过翻译后修饰的肽，具有独特的环化基序，该基序由分子内赖氨酸 - 色氨酸交联组成。来自不同链球菌属的三种自由基S - 腺苷甲硫氨酸酶，即StrB、AgaB和SuiB，已被证明以依赖前导肽的方式将这种修饰安装到它们各自的前体肽上。在此，我们进行了详细研究，以区分几种合理的机制假设，具体探讨交联形成过程中吲哚的自由基加成与亲电加成、底物侧链在酶活性位点结合中的作用以及反应循环中催化碱的身份。我们的结果与关键碳 - 碳键形成步骤的自由基亲电芳香取代机制一致。它们还阐述了支撑这种独特且具有合成挑战性的翻译后修饰的其他机制特征。
