title: A histidine-rich and cysteine-rich metal-binding domain at the C terminus of heat shock protein A from Helicobacter pylori: implication for nickel homeostasis and bismuth susceptibility.
abstract: HspA, a member of the GroES chaperonin family, is a small protein found in Helicobacter pylori with a unique histidine- and cysteine-rich domain at the C terminus. In this work, we overexpressed, purified, and characterized this protein both in vitro and in vivo. The apo form of the protein binds 2.10 +/- 0.07 Ni(2+) or 1.98 +/- 0.08 Bi(3+) ions/monomer with a dissociation constant (K(d)) of 1.1 or 5.9 x 10(-19) microm, respectively. Importantly, Ni(2+) can reversibly bind to the protein, as the bound nickel can be released either in the presence of a chelating ligand, e.g. EDTA, or at an acidic pH (pH((1/2)) 3.8 +/- 0.2). In contrast, Bi(3+) binds almost irreversibly to the protein. Both gel filtration chromatography and native electrophoresis demonstrated that apo-HspA exists as a heptamer in solution. Unexpectedly, binding of Bi(3+) to the protein altered its quaternary structure from a heptamer to a dimer, indicating that bismuth may interfere with the biological functions of HspA. When cultured in Ni(2+)-supplemented M9 minimal medium, Escherichia coli BL21(DE3) cells expressing wild-type HspA or the C-terminal deletion mutant clearly indicated that the C terminus might protect cells from high concentrations of external Ni(2+). However, an opposite phenomenon was observed when the same E. coli hosts were grown in Bi(3+)-supplemented medium. HspA may therefore play a dual role: to facilitate nickel acquisition by donating Ni(2+) to appropriate proteins in a nickel-deficient environment and to carry out detoxification via sequestration of excess nickel. Meanwhile, HspA can be a potential target of the bismuth antiulcer drug against H. pylori.
authors: Department of Chemistry and the Open Laboratory of Chemical Biology, The University of Hong Kong, Pokfulam Road, Hong Kong, China.
authors: Shujian
authors: S
authors: Cun
authors: Hongyan
authors: H
authors: Li
authors: Ruiguang
authors: R
authors: Ge
authors: Marie C M
authors: MC
authors: Lin
authors: Hongzhe
authors: H
authors: Sun
mesh_terms: D001426:Bacterial Proteins / Q000737:chemistry* / Q000235:genetics / Q000302:isolation & purification / Q000378:metabolism; D001729:Bismuth / Q000737:chemistry* / Q000627:therapeutic use; D018833:Chaperonins / Q000737:chemistry* / Q000235:genetics / Q000302:isolation & purification / Q000378:metabolism; D019281:Dimerization; D004492:Edetic Acid / Q000737:chemistry; D004926:Escherichia coli / Q000254:growth & development; D006360:Heat-Shock Proteins / Q000737:chemistry* / Q000235:genetics / Q000302:isolation & purification / Q000378:metabolism; D016481:Helicobacter Infections / Q000188:drug therapy / Q000235:genetics / Q000378:metabolism; D016480:Helicobacter pylori / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D006639:Histidine / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D006863:Hydrogen-Ion Concentration; D008667:Metalloproteins / Q000737:chemistry* / Q000235:genetics / Q000302:isolation & purification / Q000378:metabolism; D009532:Nickel / Q000737:chemistry* / Q000378:metabolism / Q000494:pharmacology; D011485:Protein Binding / Q000502:physiology; D020836:Protein Structure, Quaternary; D017434:Protein Structure, Tertiary / Q000502:physiology; D011994:Recombinant Proteins / Q000737:chemistry / Q000235:genetics / Q000302:isolation & purification / Q000378:metabolism
chemical_list: D001426:Bacterial Proteins; D006360:Heat-Shock Proteins; C113725:HspA protein, bacteria; D008667:Metalloproteins; D011994:Recombinant Proteins; D006639:Histidine; D009532:Nickel; D004492:Edetic Acid; D018833:Chaperonins; D001729:Bismuth