Helicobacter pylori nickel storage proteins: recognition and modulation of diverse metabolic targets

Nickel metabolism and trafficking in Helicobacter pylori is complex, perhaps more so than in any other pathogen. Along with nickel enzymes and their associated nickel-binding maturation machinery, H. pylori contains nickel storage proteins, Hpn and Hpnl. Through a combined crosslinking and enrichment approach, we show that Hpn/Hpnl interact with a wide array of partners; over 100 proteins were captured, including known nickel-enzyme maturation proteins, and other proteins outside known H. pylori nickel-associated proteins. The crosslinker binds to exposed amines, but there was no correlation between lysine content and the pulldown abundance of captured proteins. Phenotypic characterization of mutant strains (Δhpn, Δhpnl, or ΔhpnΔhpnl) was used to explore interactions. Nickel deprivation affected the hydrogenase activity of the ΔhpnΔhpnl strain much more severely than the wild-type (WT), whereas the activities of the single mutants were similar to WT. Leucyl aminopeptidase activity was affected in opposite ways in the mutant strains: Δhpn had a threefold decrease, while Δhpnl had a sevenfold increase, compared to the parent. Similar mutant strain analysis supported Hpn and Hpnl acting synergistically to suppress aliphatic amidase activity in a nickel-dependent manner. Recombinant amidase could bind a variety of divalent metals. Amidase activity was greatest in the mutant strains and was inhibited by exogenous nickel. The addition of pure storage protein to extracts from the mutants only restored the suppression of amidase activity for the mutant strain lacking that protein; both storage proteins are needed for amidase suppression. These results suggest that Hpn and Hpnl play more diverse roles than previously thought.