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Project Progress

The interface between mineral surfaces and early biological molecules may have played a key role in early life. Using a “top-down” approach to probing this interface, we have utilized knowledge gained from complex Fe-S cluster assembly to design an experimental pathway to examine putative early Fe-S based prebiotic catalysts. Complex Fe-S cluster assembly pathways are clearly built in a step wise fashion and involve radical chemistry (catalyzed by radical SAM enzymes) to impart unique catalytic functionality to standard Fe-S based systems. Radical SAM enzymes are found in all kingdoms of life and have been proposed to be evolutionarily ancient given their roles in central pathways including glucose and lysine metabolism, ribonucleotide reduction, DNA repair, tRNA modification and cofactor biosynthesis. Given the fundamental biochemical processes associated with radical SAM enzymes, radical SAM chemistry may have been one of the earliest functions associated with protein-based biocatalysts.

The core functionality associated with radical SAM enzymes is attributed to the presence of a site-differentiated [4Fe-4S]^2+/+ cluster that coordinates SAM; this ligand binding is the key determinate to the radical mediated homolytic S+–C5’ bond cleavage of SAM and the generation of the highly reactive 5’-deoxyadenosyl radical responsible for H-atom abstraction from the multitude of substrates that this enzyme superfamily acts on. The strict conservation of the CX3CX2C motif that harbors the site-differentiated [4Fe-4S]^2+/+ cluster, coupled to the concept of the functional diversification from a primordial (α/β)₂ TIM barrel progenitor, has given rise for the need to biochemically define polypeptides that bind redox active, site-differentiated [4Fe-4S]^2+/+ clusters. Along these lines, we have begun to explore the ability of 8-mer CX₃CX₂C based peptides to incorporate functional [4Fe-4S]^2+/+ clusters in aqueous solution and to interact with and cleave SAM. The event of a simple peptide complex capable of carrying out radical based chemistry in aqueous solution would mark a significant occasion in the growing complexity associated with an emerging biotic world.