Newly Found Enzyme Degrades 8-Oxoguanine

8-Oxoguanine (8-oxoG) is produced by oxidation of guanine in DNA and is excised during DNA repair. What happens to the free 8-oxoG after it’s removed? The answer to that question has been elusive because 8-oxoG isn’t a substrate for any known enzymes that degrade guanine. Frank M. Raushel of Texas A&M University and coworkers have now found an enzyme in the bacterium Pseudomonas aeruginosa that deaminates 8-oxoG to form uric acid (J. Am. Chem. Soc., DOI: 10.1021/ja909817d). Although the researchers have been unable to crystallize this 8-oxoG deaminase, they crystallized a homologous protein identified during environmental DNA sequencing of marine samples. The homologous protein has a single zinc ion bound to the enzyme in a similar way to what has been observed in cytosine, guanine, and adenosine deaminases. “I’m convinced there is much more to 8-oxoG and its roles in oxidative stress, from signaling to mutations, than is currently appreciated,” says nucleic acid chemist Cynthia J. Burrows of the University of Utah. “The very nice work of Raushel and coworkers adds a piece to the puzzle, or perhaps enlarges the puzzle.”