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

Iron-sulfur clusters are widespread in biological systems and participate i n a broad range of functions. These functions include electron transport, m ediation of redox as well as non-redox catalysis, and regulation of gene ex pression. A new role for iron-sulfur clusters has emerged in recent years a s a number of enzymes have been identified that utilize Fe-S clusters and S -adenosylmethionine (AdoMet) to initiate radical catalysis. This Fe-S clust er-mediated radical catalysis includes the generation of stable protein-cen tered radicals as well as generation of substrate radical intermediates, wi th evidence suggesting a common mechanism involving an intermediate adenosy l radical. Although the mechanism of generation of the adenosyl radical int ermediate is currently not well understood, it likely represents novel chem istry for iron-sulfur clusters. The purpose of this review is to present th e current state of knowledge of this newly emerging group of Fe-S/AdoMet en zymes.