Double‐Cubane [8Fe9S] Clusters: A Novel Nitrogenase‐Related Cofactor in Biology

Three different types of electron‐transferring metallo‐ATPases are able to couple ATP hydrolysis to the reduction of low‐potential metal sites, thereby energizing an electron. Besides the Fe‐protein known from nitrogenase and homologous enzymes, two other kinds of ATPase with different scaffolds and cofactors are used to achieve a unidirectional, energetic, uphill electron transfer to either reduce inactive Co‐corrinoid‐containing proteins (RACE‐type activators) or a second iron‐sulfur cluster‐containing enzyme of a unique radical enzymes family (archerases). We have found a new cofactor in the latter enzyme family, that is, a double‐cubane cluster with two [4Fe4S] subclusters bridged by a sulfido ligand. An enzyme containing this cofactor catalyzes the ATP‐dependent reduction of small molecules, including acetylene. Thus, enzymes containing the double‐cubane cofactor are analogous in function and share some structural features with nitrogenases.