The Rieske protein is an electron transport protein found in the bc1 complex that contains a [2Fe-2S] cluster ligated by two cysteines and two histidines. The Thermus thermophilus Rieske protein was probed by mutating and chemically modifying the protein. Different chemical modifiers which result in adducts of the ligating histidines that vary in electron withdrawing capabilities have been explored. Previous studies showed that diethyl pyrocarbonate (DEPC) both modifies and reduces the cluster in a pH dependent manner, likely due to the electron withdrawing properties of the adduct. A second modifier, methyl bromoacetate (MBA), modifies the histidines leaving an adduct that is less electron withdrawing. The wild type and several mutant proteins that alter the reduction potential of the cluster all react with MBA. These proteins react in a pH dependent manner like DEPC, but modification with MBA does not result in reduction of the cluster. Presently, work is being done to purify the MBA-modified Rieske proteins from the unmodified species, which would both confirm the initial results and potentially help to obtain a crystal structure of the modified protein. The current data indicates that the reduction potential of the [2Fe-2S] cluster can be altered by having adducts on the histidine ligands of varying electron withdrawing capabilities. This finding is important as it points to a way that the interaction between the Rieske protein and its substrate in the bc1 complex might influence how the electron transfer might occur.

Electron withdrawing capability of ligating histidine adducts influence the reduction potential of the [2Fe-2S] cluster of the Rieske protein

249th National Meeting (2015)

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