Monitoring Fe-S cluster occupancy across the E. coli proteome using chemoproteomics

Iron-sulfur (Fe-S) clusters are ubiquitous metallocofactors involved in redox chemistry, radical generation, and gene regulation. Common methods to monitor Fe-S clusters include spectroscopic analysis of purified proteins, and auto-radiographic visualization of radiolabeled iron distribution in proteomes. Here, we report a chemoproteomic strategy that monitors changes in the reactivity of Fe-S cysteine ligands to inform on Fe-S cluster occupancy. We highlight the utility of this platform in E. coli by: (1) demonstrating global disruptions in Fe-S incorporation in cells cultured under iron-depleted conditions; (2) determining Fe-S client proteins reliant on three scaffold/carrier proteins within the Isc Fe-S biogenesis pathway; and, (3) identifying two previously unannotated Fe-S proteins, TrhP and DppD. In summary, the chemoproteomic strategy described herein is a powerful tool that reports on Fe-S cluster incorporation directly within a native proteome, and enables the interrogation of Fe-S biogenesis pathways, and the identification of previously uncharacterized Fe-S proteins.