The zinc-ribbon domain of Helicobacter pylori HP0958: requirement for RpoN accumulation and possible roles of homologs in other bacteria

Levels of RpoN were greatly reduced in H. pylori strains that expressed the FlgZC202S or FlgZC223S variants. The FlgZC202S variant, but not the FlgZC223S variant, accumulated at levels similar to the wild-type protein. DUF164 proteins are not universally distributed and appear to be absent in several major bacterial taxa, including Cyanobacteria as well as Alpha-, Beta- and Gammaproteobacteria. With the exception of the Actinobacteria, members of which generally lack RpoN, genes encoding DUF164 proteins and RpoN are frequently found in the same genome. Interestingly, many of the DUF164 proteins in Actinobacteria and Bacteroidetes lack most or even all of the conserved cysteine residues.These findings suggest the importance of the zinc-ribbon domain of FlgZ in protecting RpoN from turnover. Since many bacteria that possess a DUF164 protein also contain RpoN, DUF164 proteins may have roles in RpoN protection or function in other bacteria.Helicobacter pylori is a member of the Epsilonproteobacteria that colonizes the human gastric mucosa where it causes a variety of gastrointestinal diseases, including acute gastritis, peptic and duodenal ulcers, B cell MALT lymphoma, and gastric adenocarcinoma [1-3]. Colonization of the gastric mucosa by H. pylori requires the bacterium to be motile [4,5], which is achieved through a cluster of polar sheathed flagella.The bacterial flagellum is a complex structure consisting of three basic substructures - the basal body, hook and filament. Dozens of genes are required for flagellar biogenesis and the expression of these genes is regulated by a transcriptional hierarchy in which genes are expressed as their products are needed for assembly [6,7]. All three of the RNA polymerase sigma (σ) factors in H. pylori are involved in flagellar biogenesis. In general, genes needed early in flagellar assembly are under control of the primary σ factor RpoD (σ80), while RpoN (σ54) is responsible for transcription of genes needed midway through flage