Adenosylmethionine-dependent iron-sulfur enzymes: versatile clusters in a radical new role

Iron-sulfur clusters are widespread in biological systems and participate in a broad range of functions. These functions include electron transport, mediation of redox as well as non-redox catalysis, and regulation of gene expression. A new role for iron-sulfur clusters has emerged in recent years as a number of enzymes have been identified that utilize Fe-S clusters and S-adenosylmethionine (AdoMet) to initiate radical catalysis. This Fe-S cluster-mediated radical catalysis includes the generation of stable protein-centered radicals as well as generation of substrate radical intermediates, with evidence suggesting a common mechanism involving an intermediate adenosyl radical. Although the mechanism of generation of the adenosyl radical intermediate is currently not well understood, it likely represents novel chemistry for iron-sulfur clusters. The purpose of this review is to present the current state of knowledge of this newly emerging group of Fe-S/AdoMet enzymes.