Helicobacter pylori has an unprecedented nitric oxide detoxifying system

The ability of pathogens to cope with the damaging effects of nitric oxide (NO), present in certain host niches and produced by phagocytes that support innate immunity, relies on multiple strategies that include the action of detoxifying enzymes. As for many other pathogens, these systems remained unknown for Helicobacter pylori. This work aimed at identifying and functionally characterizing an H. pylori system involved in NO protection. In the present work, the hp0013 gene of H. pylori is shown to be related to NO resistance, as its inactivation increases the susceptibility of H. pylori to nitrosative stress, and significantly decreases the NADPH-dependent NO reduction activity of H. pylori cells. The recombinant HP0013 protein is able to complement an NO reductase-deficient Escherichia coli strain and exhibits significant NO reductase activity. Mutation of hp0013 renders H. pylori more vulnerable to nitric oxide synthase-dependent macrophage killing, and decreases the ability of the pathogen to colonize mice stomachs. Phylogenetic studies reveal that HP0013, which shares no significant amino acid sequence similarity to the other so far known microbial NO detoxifiers, belongs to a novel family of proteins with a widespread distribution in the microbial world. H. pylori HP0013 represents an unprecedented enzymatic NO detoxifying system for the in vivo microbial protection against nitrosative stress.