Aconitase-mediated posttranscriptional regulation in Helicobacter pylori

Abstract

The gastric pathogen Helicobacter pylori is remarkable in that it is able to colonize the acidic environment of the stomach, a niche not chronically colonized by any other bacteria. H. pylori is notorious for possessing few regulatory systems. It was once thought that the stomach was a relatively stable environment, and without having competition from other bacteria, it was not necessary for H. pylori to possess an intricate regulatory system. However, as more evidence becomes available, it appears that H. pylori must be metabolically dynamic, as its response to environmental change is multifaceted and mediated by more than one regulatory system. Posttranscriptional regulation in bacteria has increasingly become recognized as playing a major role in the response to environmental stimuli. Aconitase is a bifunctional protein that acts as a posttranscriptional regulator by controlling mRNA stability. In its apo-form, aconitase binds to sequences in either the 5’ or 3’ untranslated regions (UTRs) of mRNA transcripts. Binding of apo-aconitase to the 5’ UTR inhibits ribosome-binding, thereby decreasing translation of the downstream gene. Transcript stability is enhanced when apo-aconitase binds to the 3’ UTR of transcripts, where it prevents ribonuclease degradation. The role of aconitase as a posttranscriptional regulator in H. pylori has not yet been explored. Here, I propose a global role for aconitase (AcnB) in modulating expression of proteins in H. pylori. Putative aconitase targets for regulation include those related to oxidative stress, urease and hydrogenase activities, motility, and numerous others.