Department of Biochemistry, Albert Einstein College of Medicine, Bronx, New York 10461, United States.
The Novo Nordisk Foundation Center for Biosustainability, Technical University of Denmark, Kgs. Lyngby, 2800, Denmark.
J Am Chem Soc. 2024 Jan 24;146(3):1860-1873. doi: 10.1021/jacs.3c05481. Epub 2024 Jan 12.
Biotin synthase (BioB) is a member of the Radical SAM superfamily of enzymes that catalyzes the terminal step of biotin (vitamin B7) biosynthesis, in which it inserts a sulfur atom in desthiobiotin to form a thiolane ring. How BioB accomplishes this difficult reaction has been the subject of much controversy, mainly around the source of the sulfur atom. However, it is now widely accepted that the sulfur atom inserted to form biotin stems from the sacrifice of the auxiliary 2Fe-2S cluster of BioB. Here, we bioinformatically explore the diversity of BioBs available in sequence databases and find an unexpected variation in the coordination of the auxiliary iron-sulfur cluster. After characterization, including the determination of biotin formation and representative crystal structures, we report a new type of BioB utilized by virtually all obligate anaerobic organisms. Instead of a 2Fe-2S cluster, this novel type of BioB utilizes an auxiliary 4Fe-5S cluster. Interestingly, this auxiliary 4Fe-5S cluster contains a ligated sulfide that we propose is used for biotin formation. We have termed this novel type of BioB, Type II BioB, with the 2Fe-2S cluster sacrificial BioB representing Type I. This surprisingly ubiquitous Type II BioB has implications for our understanding of the function and evolution of Fe-S clusters in enzyme catalysis, highlighting the difference in strategies between the anaerobic and aerobic world.
生物素合酶（BioB）是 Radical SAM 超家族酶的成员，它催化生物素（维生素 B7）生物合成的最后一步，在此过程中，它在脱辅基生物素中插入一个硫原子，形成噻吩环。BioB 如何完成这个困难的反应一直是争议的主题，主要围绕硫原子的来源。然而，现在人们普遍认为，插入形成生物素的硫原子来自 BioB 的辅助 2Fe-2S 簇的牺牲。在这里，我们从序列数据库中生物信息学地探索了 BioB 的多样性，并发现辅助铁-硫簇的配位存在出乎意料的变化。经过表征，包括生物素形成和代表性晶体结构的测定，我们报告了一种新型的 BioB，几乎所有专性厌氧生物都在使用。这种新型的 BioB 不使用 2Fe-2S 簇，而是利用辅助的 4Fe-5S 簇。有趣的是，这种辅助的 4Fe-5S 簇含有一个配位的硫，我们提出它用于生物素的形成。我们将这种新型的 BioB 命名为 II 型 BioB，而牺牲 2Fe-2S 簇的 I 型 BioB。这种出乎意料的普遍存在的 II 型 BioB 对我们理解酶催化中 Fe-S 簇的功能和进化具有重要意义，突出了厌氧和需氧世界之间在策略上的差异。
