Crystal Structure of Biotin Synthase, an S -Adenosylmethionine-Dependent Radical Enzyme

Abstract

The crystal structure of biotin synthase from Escherichia coli in complex with S- adenosyl- L -methionine and dethiobiotin has been determined to 3.4 angstrom resolution. This structure addresses how “AdoMet radical” or “radical SAM” enzymes use Fe 4 S 4 clusters and S- adenosyl- L -methionine to generate organic radicals. Biotin synthase catalyzes the radical-mediated insertion of sulfur into dethiobiotin to form biotin. The structure places the substrates between the Fe 4 S 4 cluster, essential for radical generation, and the Fe 2 S 2 cluster, postulated to be the source of sulfur, with both clusters in unprecedented coordination environments.