Selenocyanate Derived Se-Incorporation into the Nitrogenase Fe Protein Cluster

The nitrogenase Fe protein mediates ATP-dependent electron transfer to the nitrogenase MoFe protein during nitrogen fixation, in addition to catalyzing MoFe protein independent substrate (CO ₂ ) reduction and facilitating MoFe protein metallocluster biosynthesis. The precise role(s) of the Fe protein Fe ₄ S ₄ cluster in some of these processes remains ill-defined. Herein, we report crystallographic data demonstrating ATP-dependent chalcogenide exchange at the Fe ₄ S ₄ cluster of the nitrogenase Fe protein when potassium selenocyanate is used as the selenium source. The observed chalcogenide exchange illustrates that this Fe ₄ S ₄ cluster is capable of core substitution reactions under certain conditions, adding to the Fe protein’s repertoire of unique properties.