Oxidative damage to DNA has been implicated as an important causative agent in cancer. Oxidation of guanine leads to the formation of OG (where OG = 7,8-dihydro-8-oxoguanine) which promotes misincorporation of A during DNA replication to form OG:A base-pairs. In E.coli, two enzymes prevent mutations caused by OG; the Fpg protein removes OG from OG:C base pairs, while the MutY enzyme removes adenine from OG:A base pairs. Once the damaged or inappropriate bases are removed, they are replaced with the normal undamaged bases. Our work on delineating the basic properties of MutY was important for the subsequent work that we participated in that linked defective OG:A repair by the human homologue of MutY (hMYH) and colorectal cancer (Figure 2).

      An unusual feature of many of the base excision repair glycosylases (such as MutY/MYH) is the presence of a [4Fe-4S] cluster. This cluster plays an important role in mediating damage recognition, and recent work also indicates a role for electron-transfer chemistry in the sensing and repair of DNA damage. Along this line, we have recently also begun to investigate a unique class of [4Fe-4S] cluster containing uracil-DNA glycosylases, that are structurally distinct from MutY, but may use the metal cofactor in an analogous fashion. In collaboration with Dr. Cynthia Burrows (University of Utah), we are also examining the repair by a variety of different enzymes of the oxidized guanine lesions, spiroiminodihydantoin and guanidinohydantoin. With these lesions, repair actually may contribute to their mutageneicty and toxicity.

      As chemical biologists interested in DNA repair, we use a variety of approaches and put them together in revealing ways. The tools of enzymology are used to study the enzyme and its interactions with DNA substrates. Synthetic techniques are used to synthesize modified DNA substrates to test hypotheses about mechanism, as well as prepare analogues that are resistant to the action of the enzymes. Bioinorganic approaches are used to manipulate and evaluate the [4Fe-4S] cluster in these enzymes. Biophysical techniques are used to characterize the protein-DNA complex. The tools of cell biology and molecular biology are used to manipulate and evaluate "repair" in cells. Taken together this work makes important connections between the molecular insight derived from our in vitro studies, and how these features impact repair in cells. Ultimately this well reveal the critical features of the DNA repair process that prevents deleterious mutations leading to cancer, and how these processes may be manipulated for beneficial therapeutic purposes.