Fig. 5.

DNA-modified electrodes can be used to monitor proteins with redox-active cofactors. Here, the DNA helicase XPD which contains a [4Fe–4S] cluster is shown bound to a DNA-modified electrode. In the absence of any ATP or with the non-hydrolyzable ATP analog ATP-γ-S, a steady DNA-mediated signal from the cluster is measured (left). Upon addition of ATP, this signal increases significantly. This result reflects a conformational change in XPD during ATP hydrolysis that improves the coupling of the [4Fe–4S] cluster to the π-stack. Thus, DNA-modified electrodes report on how DNA coupling changes during protein activity and this information can provide insight into how DNA CT might be involved in the regulation and coordination of these activities.