Monday, June 18, 2007
Golden Eagle Eyrie (Boise Centre on the Grove)
139

Multidisciplinary mechanistic study of an archaeal antioxidant protein

Tyler J. Arbour, Luke M. Oltrogge, Mark A. Allen, Robert K. Szilagyi, Mark Young, and Trevor Douglas. Montana State University, Bozeman, MT

Oxidative stress poses a threat to both aerobic and anaerobic organisms due to the formation of damaging reactive oxygen species. The recently characterized Dps-like protein (SsDps-L) from the hyperthermophilic archaeon Sulfolobus solfataricus is an ideal model system for exploring the molecular strategies used by primordial organisms in response to oxidative stress. The SsDps-L forms a dodecameric cage structure that mitigates oxidative damage through the reduction of hydrogen peroxide, thereby minimizing the harmful Fenton reaction, which generates the hydroxyl radical ĽOH. This enzyme has unprecedented ability to catalyze ferritin-like iron mineralization as well as catalase-like disproportionation of hydrogen peroxide. A unique structural feature is the presence of a cysteine pair located above the active site that is conserved among all putative Dps-L proteins. These residues may play an important role in the catalytic activity and possible in vivo redox-signaling. Complementary approaches of computational modeling, mass spectrometry, and additional experimental techniques are being used to investigate this chemistry. Quantum chemical calculations were used to refine the X-ray crystal structure of the active site to atomic resolution, providing a virtual chemical model for possible reaction mechanisms. Proteolytic digestion and HPLC/ESI-MS were employed to track changes in the oxidation state of the cysteines over a range of reaction conditions, thereby probing their role in catalysis. These studies lead to insights into the mechanistic details of the response to oxidative stress, and hold implications for similar processes in higher organisms.