DNA metabolism in extremophiles Structure-function studies of proteins involved in DNA repair and replication from Aliivibrio salmonicida and Deinococcus radiodurans

Abstract

Deinococcus radiodurans is a gram-positive bacterium with a pink-orange colour first isolated in canned meat. The bacteria is remarkable amongst all species studied to date by its unusual ability to repair hundreds of radiation induced DNA double strand breaks where normal species can only repair a dozen. Our studies of the DNA polymerase III β-subunit (β-clamp) and Exonuclease III from D. radiodurans indicates that they both have developed properties to support efficient replication (β-clamp) and DNA-repair (ExoIII) in this radiation-resistance and desiccation tolerant organisms.

A vast amount of the Earth consists of cold environments, including deep see waters and Polar regions. Organisms found in these areas have to adapt to their surrounding environment, and are dependent on possessing enzymes with an acceptable activity and stability at low temperatures in order to maintain the functionality of their cellular machinery. Aliivibrio salmonicida is a psychrophilic fish pathogen bacterium which has an optimal growth temperature around 12°C. We found the enzyme MutT from A. salmonicida capable of efficiently hydrolyzing the oxidative damaged nucleotide, 8-oxodGTP, in the nucleotide pool at low temperatures, thus preventing the oxidized nucleotide from being incorporated into genomic DNA as part of a counterattack on the hosts, A. salmonicida, attempt to kill the bacteria by producing a high level of oxygen radicals upon infection.