title: Pyruvate formate-lyase activating enzyme: elucidation of a novel mechanism for glycyl radical formation.
abstract: Pyruvate formate lyase activating enzyme is a member of a novel superfamily of enzymes that utilize S-adenosylmethionine to initiate radical catalysis. This enzyme has been isolated with several different iron-sulfur clusters, but single turnover monitored by EPR has identified the [4Fe-4S](1+) cluster as the catalytically active cluster; this cluster is believed to be oxidized to the [4Fe-4S](2+) state during turnover. The [4Fe-4S] cluster is coordinated by a three-cysteine motif common to the radical/S-adenosylmethionine superfamily, suggesting the presence of a unique iron in the cluster. The unique iron site has been confirmed by Mossbauer and ENDOR spectroscopy experiments, which also provided the first evidence for direct coordination of S-adenosylmethionine to an iron-sulfur cluster, in this case the unique iron of the [4Fe-4S] cluster. Coordination to the unique iron anchors the S-adenosylmethionine in the active site, and allows for a close association between the sulfonium of S-adenosylmethionine and the cluster as observed by ENDOR spectroscopy. The evidence to date leads to a mechanistic proposal involving inner-sphere electron transfer from the cluster to the sulfonium of S-adenosylmethionine, followed by or concomitant with C-S bond homolysis to produce a 5'-deoxyadenosyl radical; this transient radical abstracts a hydrogen atom from G734 to activate pyruvate formate lyase.
authors.affiliation: Department of Chemistry, Michigan State University, East Lansing, MI 48824, USA.
authors.forename: Jeffrey M
authors.initials: JM
authors.lastname: Buis
authors.forename: Joan B
authors.initials: JB
authors.lastname: Broderick
mesh_terms: D000123:Acetyltransferases; D001665:Binding Sites; D002384:Catalysis; D004578:Electron Spin Resonance Spectroscopy; D004579:Electron Transport; D004789:Enzyme Activation; D004798:Enzymes / Q000737:chemistry* / Q000378:metabolism*; D005609:Free Radicals / Q000737:chemistry*; D007506:Iron-Sulfur Proteins / Q000737:chemistry* / Q000378:metabolism; D012436:S-Adenosylmethionine / Q000378:metabolism; D015204:Spectroscopy, Mossbauer; D013379:Substrate Specificity
chemical_list: D004798:Enzymes; D005609:Free Radicals; D007506:Iron-Sulfur Proteins; D012436:S-Adenosylmethionine; D000123:Acetyltransferases; C040285:pyruvate formate-lyase activating enzyme