Distinct Modulation of Helicobacter pylori HtrA Activity by Divalent Transition Metals, Impacting HtrA Stability, Oligomerization and E-Cadherin Shedding

The Group-1 carcinogen <i>Helicobacter pylori</i> (<i>H. pylori</i>) secretes the serine protease high-temperature requirement A (HtrA), which is directly involved in the disruption of the epithelial barrier in the stomach. HtrA cleaves the extracellular domains of junctional proteins, including E-cadherin (CDH1), claudin-8, occludin, or desmoglein-2, to open intercellular adhesions, allowing <i>H. pylori</i> to transmigrate to subepithelial regions of the gastric mucosa. In our previous work, we found that Zn²⁺ and Cu²⁺ ions efficiently blocked the HtrA activity. However, the impact of other divalent ions on HtrA activity is rather unknown. In this report, we unexpectedly found a stimulating effect through Mn²⁺, Ni²⁺ and Co²⁺ ions on HtrA oligomerization and activity. In contrast to other tested ions, increasing concentrations of Mn²⁺, Ni²⁺ and Co²⁺ strongly enhanced HtrA multimerization as determined in SDS-PAGE under non-reducing conditions and in casein zymography. Increased proteolytic activity of HtrA was further assessed in in vitro cleavage experiments using casein and CDH1 as substrates. Mechanistically, divalent ions bound to HtrA and induced an active conformation, which strongly increased CDH1 cleavage in vitro. The importance of enhanced HtrA activity was finally underlined by the analysis of CDH1 cleavage in <i>H. pylori</i> infection experiments, showing that Ni²⁺ potentiated HtrA-mediated CDH1 shedding. In summary, this study demonstrates that divalent ions exhibit different effects on HtrA activity and that Ni²⁺ and Co²⁺ enhance proteolytic activity by promoting oligomerization, suggesting that metal availability in the gastric environment affects <i>H. pylori</i> virulence.