Strategically chosen peptides enable the creation of maquettes of [4Fe-4S] containing metalloenzymes as synthetic biological platforms for structure-function studies. This is promising for investigating the mechanistic details of radical S-adenosylmethionine (SAM) metalloenzymes, which utilize a conserved Cx3Cx2C motif to coordinate a redox active [4Fe-4S] cluster. A unique Fe site of the cluster anchors SAM in a bidentate manner through its carboxylate and amine groups, which facilitates reductive cleavage of a specific S+-C(5’) bond via an inner-sphere process to generate the 5’-deoxyadenosyl radical species. This radical carries out an array of substrate-derived H-atom abstraction events, leading to the premise that this motif acts as Nature’s preferred radical [Fe-S] catalytic system. Prior studies focused on ferredoxin (Fd) maquettes and demonstrated that redox active [4Fe-4S] cluster reconstitution is possible in aqueous solutions under strict anaerobic conditions. Our work complements and extends these prior studies by developing peptide-based radical SAM maquettes. We provide an update in our progress using a series of peptides containing the Fd Cx2Cx2C and the radical SAM Cx3Cx2C canonical cluster binding motifs. [Fe-S] cluster reconstitution was monitored by UV-vis and EPR spectroscopic techniques. Tested sequences were observed to reconstitute with similar high efficiencies; however, the redox stability did vary greatly. By exploring Cx3Cx2C motifs in aqueous solution, our work contributes to understanding the fundamental structural and compositional elements that define [4Fe-4S] cluster nesting.

Radical SAM maquette chemistry: Cx3Cx2C peptide coordinated redox active [4Fe-4S] clusters

2019 Spring National Meeting

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