A Consensus Mechanism for Radical SAM-Dependent Dehydrogenation? BtrN Contains Two [4Fe-4S] Clusters

BtrN catalyzes the two-electron oxidation of the C3 secondary alcohol of 2-deoxy-scyllo-inosamine to the corresponding ketone and is a member of a subclass of radical S-adenosylmethionine (SAM) enzymes called radical SAM (RS) dehydrogenases. Like all RS enzymes, BtrN contains a [4Fe-4S] cluster that delivers an electron to SAM, inducing its cleavage to the common intermediate in RS reactions, the 5'-deoxyadenosyl 5'-radical. In this work, we show that BtrN contains an additional [4Fe-4S] cluster, thought to bind in contact with the substrate to facilitate loss of the second electron in the two-electron oxidation.