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

Abstract

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.

Recent advances in bioinorganic chemistry of bismuth

“…To validate the potential targets of bismuth drugs identified by metalloproteomic approach subsequent studies have been carried out [51,52 ,53]. For example, fumarase, an enzyme that catalyzes the reversible hydration of fumarate to malic acid, binds one Bi 3+ per monomer, leading to an apparent non-competitive inhibition of the enzyme [53]. HspA, a member of the GroES chaperonin family, is a small protein with a unique histidine/ cysteine-rich domain at the C terminus with the sequence shown in Figure 3a.…”

Bismuth nanoparticles obtained by a facile synthesis method exhibit antimicrobial activity againstStaphylococcus aureusandCandida albicans

“…The mechanisms of action of bismuth (III) ions are partially known. Ionic bismuth binds to glutathione, which improves its translocation inside of cells, from where it targets proteins and inhibit enzymes, such as urease and fumarase [59,60]. Regarding the bismuth-BAL complex, the mechanisms related to their antimicrobial activity are not fully understood.…”

“…5E ). This may be caused by the effects of bismuth on the cells, such as the denaturing of proteins [59,60] and changes in the cell membrane permeability [61]. Other potential mechanisms remain to be further studied and elucidated.…”

Colloidal bismuth subcitrate impedes proton entry into Helicobacter pylori and increases the efficacy of growth‐dependent antibiotics

“…Most proposed mechanisms centre around enzyme inhibition, metal interference, or bacterial structure and adherence. Bismuth can bind fumarase, part of the tricarboxylic acid cycle, impacting bacterial energetics or motility via decreased flagellar rotation, but this again raises the question of the degree of bismuth access to the enzyme in vivo . Hpn, an H. pylori protein that binds nickel and zinc, has been assumed to bind bismuth, and mutant strains lacking the protein are four times more sensitive to CBS, but this also assumes significant bismuth uptake and does not definitively predict mechanism.…”