The interaction of a histidine-rich protein hpn with the membrane mimics: implications for pathologic roles of Hpn in Helicobacter pylori.

BACKGROUND: Hpn is a small histidine-rich protein in Helicobacter pylori. This protein has been shown to play roles in nickel storage and detoxification and to exhibit cytotoxicity to gastric epithelial cells. Hpn can be secreted outside of the bacterium and forms amyloid-like structures. OBJECTIVE: To study the interactions between Hpn and membrane mimics, which may further our understanding of the pathologic roles of this bacterium. METHODS: Various biochemical and biophysical methods, such as secondary structure determination be CD, calcein release assay with fluorescence spectrometry, and Laurdan and Prodan generalized polarization determination have been used to characterize the interaction between Hpn and membrane mimics. RESULTS: Membrane mimics induced the formation of α-helix in Hpn. The interaction disrupts the integrity of the membrane mimics and leads to the release of inner calcein probe. The experiments involving the Laurdan and Prodan fluorescence indicated that increasing the total protein/lipid ratio leads to a less ordered and more hydrated lipid membrane structure close to the water/lipid interface of lipid bilayers modeling the mitochondrial inner membrane. CONCLUSION: The present data indicated that Hpn may take part in the pathological roles of Helicobacter pylori through membrane interactions.

The actions of bismuth in the treatment of Helicobacter pylori infections: an update.

Helicobacter pylori causes various gastric diseases, such as gastritis, peptic ulcerations and gastric cancer. Bismuth-based triple or quadruple therapies have been commonly recommended for the treatment of H. pylori infections. Up to now, the molecular mechanisms by which bismuth inhibits the growth of H. pylori are far from clear. The present concise review intends to cover the most recent reports and discoveries in the field of the inhibitory mechanism of bismuth against H. pylori as well as the bacterial protective response to drug treatment, which will help us to further understand the molecular mechanisms underlying the actions of metal-based drugs and stimulate further development of effective anti-bacterial drugs.

Inhibition of fumarase by bismuth(III): implications for the tricarboxylic acid cycle as a potential target of bismuth drugs in Helicobacter pylori.

Helicobacter pylori causes various gastric diseases, such as gastritis, peptic ulcerations and gastric cancer. Triple therapy combining bismuth compounds with two antibiotics is the cornerstone of the treatment of H. pylori infections. Up to now, the molecular mechanisms by which bismuth inhibits the growth of H. pylori are far from clear. In the bacterial tricarboxylic acid (TCA) cycle, fumarase catalyses the reversible hydration of fumarate to malic acid. Our previous proteomic work indicated that fumarase was capable of bismuth-binding. The interactions as well as the inhibitory effects of bismuth to fumarase have been characterized in this study. The titration of bismuth showed that each fumarase monomer binds one mol equiv of Bi(3+), with negligible secondary structural change. Bismuth-binding results in a near stoichiometric inactivation of the enzyme, leading to an apparent non-competitive mechanism as reflected by the Lineweaver-Burk plots. Our collective data indicate that the TCA cycle is a potential molecular target of bismuth drugs in H. pylori.

Histidine-rich protein Hpn from Helicobacter pylori forms amyloid-like fibrils in vitro and inhibits the proliferation of gastric epithelial AGS cells.

Helicobacter pylori causes various gastric diseases, such as gastritis, peptic ulcerations, gastric cancer and mucosa-associated lymphoid tissue lymphoma. Hpn is a histidine-rich protein abundant in this bacterium and forms oligomers in physiologically relevant conditions. In this present study, Hpn oligomers were found to develop amyloid-like fibrils as confirmed by negative stain transition electron microscopy, thioflavin T and Congo red binding assays. The amyloid-like fibrils of Hpn inhibit the proliferation of gastric epithelial AGS cells through cell cycle arrest in the G2/M phase, which may be closely related to the disruption of mitochondrial bioenergetics as reflected by the significant depletion of intracellular ATP levels and the mitochondrial membrane potential. The collective data presented here shed some light on the pathologic mechanisms of H. pylori infections.