The zinc-binding fragment of HypA from Helicobacter pylori: a tempting site also for nickel ions

The effect of side chains on the complex formation processes of N-terminally free hexapeptides containing C-terminal cysteinyl functions

Ratio of isomers of 1 to 1 nickel-ligand complexes formed in equimolar systems at pH 11 (left) and pH 7 (right) showing the influence of an internal coordinating side chain.

Metal Binding Ability of Small Peptides Containing Cysteine Residues

The Cd(II)-, Pb(II)-, Ni(II)- and Zn(II)-complexes of small terminally protected peptides containing CXXX, XXXC, XCCX, CXn C (n=1-3) sequences have been studied with potentiometric, UV/Vis and CD spectroscopic techniques. The cysteine thiolate group is the primary binding site for all studied metal ions, but the presence of a histidyl or aspartyl side chain in the molecule contributes to the stability of the complexes. For two-cysteine containing peptides the (S- ,S- ) coordinated species are formed in the physiological pH range and the stability increases in the Ni(II) Collapse

Key Words

• cysteine containing peptides
• metal complexes
• selectivity
• spectroscopic measurements
• stability constant

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MESH Headings

• Amino Acid Sequence
• Chelating Agents/chemistry
• Coordination Complexes/chemistry
• Cysteine/chemistry
• Ligands
• Metals, Heavy/chemistry
• Molecular Structure
• Oligopeptides/chemistry

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Grants

• European Regional Development Fund

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Affiliation(s)

Márton Lukács Department of Inorganic and Analytical ChemistryUniversity of DebrecenEgyetem tér 14032DebrecenHungary
Dóra Csilla Pálinkás Department of Inorganic and Analytical ChemistryUniversity of DebrecenEgyetem tér 14032DebrecenHungary
Györgyi Szunyog Department of Inorganic and Analytical ChemistryUniversity of DebrecenEgyetem tér 14032DebrecenHungary
Katalin Várnagy Department of Inorganic and Analytical ChemistryUniversity of DebrecenEgyetem tér 14032DebrecenHungary

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Histidine tracts in human transcription factors: insight into metal ion coordination ability

Consecutive histidine repeats are chosen both by nature and by molecular biologists due to their high affinity towards metal ions. Screening of the human genome showed that transcription factors are extremely rich in His tracts. In this work, we examine two of such His-rich regions from forkhead box and MAFA proteins-MB3 (contains 18 His) and MB6 (with 21 His residues), focusing on the affinity and binding modes of Cu2+ and Zn2+ towards the two His-rich regions. In the case of Zn2+ species, the availability of imidazole nitrogen donors enhances metal complex stability. Interestingly, an opposite tendency is observed for Cu2+ complexes at above physiological pH, in which amide nitrogens participate in binding.

Antimicrobial peptide–metal ion interactions – a potential way of activity enhancement

We discuss the potential correlation between the antimicrobial peptide–metal binding mode, structure, thermodynamics and mode of action.

Metal interactions with the transmembrane region of HupE Ni2+ transporter explain its efficiency

Efficient nickel transport is crucial for the survival and virulence of various bacteria and fungi, with Ni²⁺ being required for the activity of nine enzymes such as [NiFe] hydrogenase, which catalyzes the reversible oxidation of molecular hydrogen for energy production. This work focuses on a region of transmembrane domain I from the HupE nickel transporter, highly conserved in the HupE/UreJ and NiCoT permease families, analyzing its interactions with native Ni²⁺ and two other metal ions (Cu²⁺ and Zn²⁺), which might interfere with nickel binding. Metal coordination sites are pointed out and thermodynamic parameters are discussed in detail. Their comparison to the previously studied periplasmic metal binding region satisfies our chemical curiosity and allows to draw conclusions about HupE metal specificity. The results of this study explain one of the reasons why HupE is a medium-affinity and low-capacity transporter - its periplasmic region, ₂₂HVGLHADGTLAGLN₃₅, binds Ni²⁺ with much higher affinity than the transmembrane ₃₆HPFSGLDH₄₃ one, which should transport the metal inside the cell. Moreover, the specificity of the transmembrane region is similar to that of the periplasmic one and to that of the full-length HupE - Cu²⁺ ions are able to outcompete Ni²⁺.

Nickel Metallochaperones: Structure, Function, and Nickel-Binding Properties

Nickel-containing enzymes catalyze a series of important biochemical processes in both prokaryotes and eukaryotes. The maturation of the enzymes requires the proper assembly of the nickel-containing active sites, which involves a battery of nickel metallochaperones that exert metal delivery and storage functions. “Cross-talk” also exists between different nickel enzyme maturation processes. This chapter summarizes the updated knowledge about the nickel chaperones based on biochemical and structural biology research, and discusses the possible nickel delivery mechanisms.

[NiFe]-Hydrogenase Maturation

[NiFe]-hydrogenases catalyze the reversible conversion of hydrogen gas into protons and electrons and are vital metabolic components of many species of bacteria and archaea. At the core of this enzyme is a sophisticated catalytic center comprising nickel and iron, as well as cyanide and carbon monoxide ligands, which is anchored to the large hydrogenase subunit through cysteine residues. The production of this multicomponent active site is accomplished by a collection of accessory proteins and can be divided into discrete stages. The iron component is fashioned by the proteins HypC, HypD, HypE, and HypF, which functionalize iron with cyanide and carbon monoxide. Insertion of the iron center signals to the metallochaperones HypA, HypB, and SlyD to selectively deliver the nickel to the active site. A specific protease recognizes the completed metal cluster and then cleaves the C-terminus of the large subunit, resulting in a conformational change that locks the active site in place. Finally, the large subunit associates with the small subunit, and the complete holoenzyme translocates to its final cellular position. Beyond this broad overview of the [NiFe]-hydrogenase maturation process, biochemical and structural studies are revealing the fundamental underlying molecular mechanisms. Here, we review recent work illuminating how the accessory proteins contribute to the maturation of [NiFe]-hydrogenase and discuss some of the outstanding questions that remain to be resolved.

Specificity of the Zn2+, Cd2+and Ni2+ion binding sites in the loop domain of the HypA protein

The role of the residues in the hypa loop on the stability of its complexes with Zn²⁺, Cd²⁺and Ni²⁺ions.

The specificity of interaction of Zn(2+), Ni(2+) and Cu(2+) ions with the histidine-rich domain of the TjZNT1 ZIP family transporter

The Zrt/Irt-like protein (ZIP) family contributes to the metal homeostasis by regulating the transport of divalent metal cations such as Fe(2+), Zn(2+), Mn(2+), Cd(2+) and sometimes even Cu(2+). Most ZIP members have a long variable loop between transmembrane domains (TMDs) III and IV; this region is predicted to be located in the cytoplasm and is postulated to be the metal ion binding site. In this study, we looked at the thermodynamic behavior and coordination chemistry of Zn(2+), Ni(2+) and Cu(2+) complexes with the histidine-rich domain, Ac-(185)RAHAAHHRHSH(195)-NH2 (HRD), from the yeast TjZNT1 protein, located between TMDs III and IV. The sequence is conserved also in higher species like Thlaspi japonicum. The stability of complexes increases in the series Ni(2+) < Zn(2+)≪ Cu(2+). The geometry of complexes is very different for each metal and in the case of Zn(2+) complexes, high specificity in binding is observed. Moreover, the stability of HRD-Cu(2+) complexes was compared with the five His residues containing peptide from Hpn protein (Helicobacter pylori). The results suggest a high ability of HRD in the binding of all three studied metals.

Ni2+chemistry in pathogens – a possible target for eradication

Nickel homeostasis inHelicobacter pyloriand potential histidine-rich binding sites from various bacterial and fungal pathogens are discussed.

Nickel trafficking system responsible for urease maturation in Helicobacter pylori

Helicobacter pylori (H. pylori) is a common human pathogen responsible for various gastric diseases. This bacterium relies on the production of urease and hydrogenase to inhabit the acidic environment of the stomach. Nickel is an essential cofactor for urease and hydrogenase. H. pylori has to uptake sufficient nickel ions for the maturation of urease, and on the other way, to prevent the toxic effects of excessive nickel ions. Therefore, H. pylori has to strike a delicate balance between the import of nickel ions, its efficient intracellular storage, and delivery to nickel-dependent metalloenzymes when required. The assembly and maturation of the urease enzyme is a complex and timely ordered process, requiring various regulatory, uptake, chaperone and accessory proteins. In this review, we focus on several nickel trafficking proteins involved in urease maturation: NikR, NixA, HypAB, UreEFGH, HspA, Hpn and Hpnl. The work will deepen our understanding of how this pathogenic bacterium adapts to severe habitant environments in the host.