ATP-stimulated DNA-mediated charge transport by the repair helicase XPD

Abstract

The XPD helicase contains a redox active [4Fe-4S] cluster and the protein is required for both nucleotide excision repair and transcription. Using ATPase and helicase mutants of XPD, we have demonstrated that the DNA-bound redox signal is a sensitive reporter of ATP hydrolysis and reports on DNA conformational changes assocd. with enzymic function. Other XPD mutants, which are assocd. with disease, show low abs. signals without ATP, reflecting poor protein/DNA electronic coupling. In an AFM assay, monitoring the first step in searching for lesions, those mutants that show low electronic signaling are unable to redistribute onto DNA strands contg. a single base mismatch. This reduced efficiency in DNA-mediated signaling may therefore be implicated in diseases assocd. with DNA repair. Therefore, we have begun exploring the in vivo effects of varying CT proficiency in both yeast Rad3 and SaXPD proteins to explore the biol. consequences of deficiencies in DNA-mediated signaling.