Aconitase Functions as a Pleiotropic Posttranscriptional Regulator in Helicobacter pylori

Posttranscriptional regulation in bacteria has increasingly become recognized as playing a major role in response to environmental stimuli. Aconitase is a bifunctional protein that not only acts enzymatically but also can be a posttranscriptional regulator. To investigate protein expression regulated by Helicobacter pylori AcnB in response to oxidative stress, a global proteomics study was conducted wherein the ΔacnB strain was compared to the parent strain when both strains were O2 stressed. Many proteins, including some involved in urease activity, in combating oxidative stress, and in motility, were expressed at a significantly lower level in the ΔacnB strain. A bioinformatics prediction tool was used to identify putative targets for aconitase-mediated regulation, and electrophoretic mobility shift assays demonstrated that apo-AcnB is able to bind to RNA transcripts of hpn (encoding a nickel-sequestering protein), ahpC (encoding alkyl hydroperoxide reductase), and flgR (encoding flagellum response regulator). Compared to the wild type (WT), the ΔacnB strain had decreased activities of the nickel-containing enzymes urease and hydrogenase, and this could be correlated with lower total nickel levels within ΔacnB cells. Binding of apo-AcnB to the hpn 5' untranslated region (UTR) may inhibit the expression of Hpn. In agreement with the finding that AcnB regulates the expression of antioxidant proteins such as AhpC, ΔacnB cells displayed oxidative-stress-sensitive phenotypes. The ΔacnB strain has a lesser motility ability than the WT strain, which can likely be explained by the functions of AcnB on the FlgRS-RpoN-FlgE regulatory cascade. Collectively, our results suggest a global role for aconitase as a posttranscriptional regulator in this gastric pathogen.

Bacterial survival depends on the ability of the cell to sense and respond to a variety of environmental changes. For Helicobacter pylori, responding to environmental stimuli within the gastric niche is essential for persistence and host colonization. However, there is much to be learned about the regulatory mechanisms that H. pylori employs to orchestrate its response to different stimuli. In this study, we explore the role of aconitase, a bifunctional protein that has been found to act as a posttranscriptional regulator in several other bacteria. Our results shed light on the magnitude of aconitase-mediated regulation in H. pylori, and we propose that aconitase acts as a global regulator of key genes involved in virulence.