Genetic organization and enzymatic activity of a superoxide dismutase from the microaerophilic human pathogen, Helicobacter pylori.

Helicobacter pylori (Hp) is a microaerobic human pathogen that has been implicated as a factor in the development of chronic type-B gastritis, gastric ulcers and gastric carcinoma. The enzyme superoxide dismutase (SOD), a major defense mechanism against oxidative damage, catalyzes the breakdown of superoxide radicals to hydrogen peroxide and dioxygen. A search for sod genes in Hp, employing PCR, revealed that this bacterium contained at least one sod gene. We cloned and sequenced a sod from this organism and determined that the deduced protein encoded by this gene was most similar to an iron SOD (FeSOD). Northern blot and primer extension analysis of Hp RNA showed that the cloned gene is monocistronic and is probably transcribed from a sigma 70-like promoter. Assays for SOD activities, accompanied by inhibition studies, demonstrated that Hp produces an FeSOD. No other SOD activities were seen.