Electrochemical Resolution of the [4Fe-4S] Centers of the AdoMet Radical Enzyme BtrN: Evidence of Proton Coupling and an Unusual, Low-Potential Auxiliary Cluster

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• 作者：Stephanie J. Maiocco ; Tyler L. Grove ; Squire J. Booker ; Sean J. Elliott
• 刊名：Journal of the American Chemical Society
• 出版年：2015
• 出版时间：July 15, 2015
• 年：2015
• 卷：137
• 期：27
• 页码：8664-8667
• 全文大小：271K
• ISSN：1520-5126

文摘

The S-adenosylmethionine (AdoMet) radical superfamily of enzymes includes over 113鈥?00 unique members, each of which contains one indispensable iron鈥搒ulfur (FeS) cluster that is required to generate a 5鈥?deoxyadenosyl 5鈥?radical intermediate during catalysis. Enzymes within several subgroups of the superfamily, however, have been found to contain one or more additional FeS clusters. While these additional clusters are absolutely essential for enzyme activity, their exact roles in the function and/or mechanism of action of many of the enzymes are at best speculative, indicating a need to develop methods to characterize and study these clusters in more detail. Here, BtrN, an AdoMet radical dehydrogenase that catalyzes the two-electron oxidation of 2-deoxy-scyllo-inosamine to amino-dideoxy-scyllo-inosose, an intermediate in the biosynthesis of 2-deoxystreptamine antibiotics, is examined through direct electrochemistry, where the potential of both its AdoMet radical and auxiliary [4Fe-4S] clusters can be measured simultaneously. We find that the AdoMet radical cluster exhibits a midpoint potential of 鈭?10 mV, while the auxiliary cluster exhibits a midpoint potential of 鈭?65 mV, to our knowledge the lowest [4Fe-4S]^2+/+ potential to be determined to date. The impact of AdoMet binding and the pH dependence of catalysis are also quantitatively observed. These data show that direct electrochemical methods can be used to further elucidate the chemistry of the burgeoning AdoMet radical superfamily in the future.