Rieske proteins play an essential role in electron transfer in the bc1 complex. Rieske proteins contain a [2Fe-2S] cluster with one iron ligated by two histidine residues and the other iron ligated by two cysteine residues. All Rieske proteins have been shown to have pH-dependent reduction potentials with the histidines ligating the cluster deprotonating in response to increases in pH. The chemical reactivity of the ligating histidines of the Thermus thermophilus Rieske protein was tested with diethy pyrocarbonate (DEPC) over a range of pH values and with a wide range of DEPC concentrations. The modification was followed by both UV-visible and circular dichroism spectroscopies. The concentration of the modifier, DEPC has a large effect on the reaction and there is a marked difference between a 1:1 mol ratio of DEPC: protein versus ~10 fold excess. Adding concentrated acid to the modification can also quench the reaction. Analysis by mass spectrometry is also used to help determine which residue(s) is(are) most reactive. Characterization of the DEPC-modified Rieske protein is a way to analyze the effects of small molecules that inhibit the function of the bc1 complex and that have been shown to interact with the ligating histidines of the Rieske [2Fe-2S] cluster.

Investigating the chemical reactivity of histidines in the Rieske protein from <i>Thermus thermophilus</i>

248th National Meeting (2014)

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Investigating the chemical reactivity of histidines in the Rieske protein from Thermus thermophilus