Phytochelatins Bind Zn(II) with Micro- to Picomolar Affinities without the Formation of Binuclear Complexes, Exhibiting Zinc Buffering and Muffling Rather than Storing Functions.

Phytochelatins (PCs) are poly-Cys peptides containing a repeating γ-Glu-Cys motif synthesized in plants, algae, certain fungi, and worms by PC synthase from reduced glutathione. It has been shown that an excess of toxic metal ions induces their biosynthesis and that they are responsible for the detoxification process. Little is known about their participation in essential metal binding under nontoxic, basal conditions under which PC synthase is active.

An Extremely Stable Interprotein Tetrahedral Hg(Cys) Core Forms in the Zinc Hook Domain of Rad50 Protein at Physiological pH.

Invited for the cover of this issue is the group of Artur Krężel at the University of Wrocław in collaboration with Lars Hemmingsen at The University of Copenhagen and Eva Freisinger at the University of Zürich. The image depicts the outcomes of Hg interactions with Rad50 protein. Read the full text of the article at 10.

An Extremely Stable Interprotein Tetrahedral Hg(Cys) Core Forms in the Zinc Hook Domain of Rad50 Protein at Physiological pH.

In nature, thiolate-based systems are the primary targets of divalent mercury (Hg ) toxicity. The formation of Hg(Cys) cores in catalytic and structural protein centers mediates mercury's toxic effects and ultimately leads to cellular damage. Multiple studies have revealed distinct Hg -thiolate coordination preferences, among which linear Hg complexes are the most commonly observed in solution at physiological pH.

Phytochelatins as a Dynamic System for Cd(II) Buffering from the Micro- to Femtomolar Range.

Phytochelatins (PCs) are short Cys-rich peptides with repeating γ-Glu-Cys motifs found in plants, algae, certain fungi, and worms. Their biosynthesis has been found to be induced by heavy metals-both biogenic and toxic. Among all metal inducers, Cd(II) has been the most explored from a biological and chemical point of view.

Structural analysis of copper(I) interaction with amyloid β peptide.

The N-terminal fragment of Aβ (β = beta) peptide is able to bind essential transition metal ions like, copper, zinc and iron. Metal binding usually occurs via the imidazole nitrogens of the three His residues which play a key role in the coordination chemistry. Among all the investigated systems, the interaction between copper and Amyloid β assume a biological relevance because of the interplay between the two copper oxidation states, Cu(II) and Cu(I), and their involvement in redox reactions.

HENRYK - An endless source of metal coordination surprises.

The basic knowledge about biological inorganic chemistry, thermodynamics and metal binding sites of metalloproteins is crucial for the understanding of their metal binding-structure-function relationship. Metal-peptide complexes are useful and commonly used models of metal-enzyme active sites, among which copper and zinc models are one of the most extensively studied. HENRYK is a peptide sequence present in numerous proteins, and serves as a potentially tempting binding site for Cu and Zn.

Specific binding modes of Cu(I) and Ag(I) with neurotoxic domain of the human prion protein.

Prion diseases are neurodegenerative disorders associated with a conformational change of the normal cellular isoform of the prion protein (PrP(C)) to an abnormal scrapie isoform (PrP(Sc)). human prion protein (hPrP(C)) is able to bind up to six Cu(II) ions. Four of them are distributed in the octarepeat domain, containing four tandem-repetitions of the sequence PHGGGWGQ.

Impact of SDS surfactant on the interactions of Cu(2+) ions with the amyloidogenic region of human prion protein.

Prion diseases, known as Transmissible Spongiform Encephalopathies (TSEs), are a group of fatal neuronal, and to some extent infectious disorders, associated with a pathogenic protein agent called prion protein (PrP). The human prion protein (hPrP) fragment encompassing the 91-127 region, also known as the amyloidogenic domain, comprises two copper-binding sites corresponding to His-96 and His-111 residues that act as anchors for Cu(2+) binding. In this work, we investigated Cu(2+) interaction with hPrP91-127 in the presence of the anionic surfactant sodium dodecyl sulfate (SDS), which induces a partial α-helix folding of the peptide.

Metal ion mediated transition from random coil to β-sheet and aggregation of Bri2-23, a natural inhibitor of Aβ aggregation.

Furin-dependent maturation of the BRI2 protein generates the Bri2-23 fragment that is able to arrest the aggregation of amyloidβ, the peptide implicated in Alzheimer's disease (AD). Bri2-23 contains cysteines at positions 5 and 22, which are likely to bind to metal ions such as Cu(i). Metal ions may play a role in the etiology of neurodegenerative disorders such as AD, and in this work we explore the metal ion induced folding and aggregation of Bri2-23 using Hg(ii) and Ag(i) as spectroscopic probes with structural and ligand preferences similar to those of Cu(i), while not displaying redox activity under the experimental conditions.

Copper-induced structural propensities of the amyloidogenic region of human prion protein.

Transmissible spongiform encephalopathies are associated with the misfolding of the cellular Prion Protein (PrP(C)) to an abnormal protein isoform, called scrapie prion protein (PrP(Sc)). The structural rearrangement of the fragment of N-terminal domain of the protein spanning residues 91-127 is critical for the observed structural transition. The amyloidogenic domain of the protein encloses two copper-binding sites corresponding to His-96 and His-111 residues that act as anchors for metal ion binding.

Probing the coordination environment of the human copper chaperone HAH1: characterization of Hg(II)-bridged homodimeric species in solution.

Although metal ion homeostasis in cells is often mediated through metallochaperones, there are opportunities for toxic metals to be sequestered through the existing transport apparatus. Proper trafficking of Cu(I) in human cells is partially achieved through complexation by HAH1, the human metallochaperone responsible for copper delivery to the Wilson and Menkes ATPase located in the trans-Golgi apparatus. In addition to binding copper, HAH1 strongly complexes Hg(II), with the X-ray structure of this complex previously described.

Polythiol binding to biologically relevant metal ions.

The coordination properties of three peptides with CXXC motif: Ac-GCASCDNCRACKK-NH(2), Ac-GCASCDNCRAAKK-NH(2) and Ac-GCASCDNARAAKK-NH(2) as donors of four, three and two thiol ligands for Ni(2+),Cd(2+), Zn(2+) and Bi(3+) were studied by potentiometric titrations, UV-Vis and CD spectra measurements. Since the stability of the complexes is closely connected with the amount of the metal-bound cysteine sulfurs, competition plots of the complexes of peptides with 2, 3 and 4 cysteines further prove the involvement of all thiols in the metal ion binding. Furthermore, the sulfur-bound zinc complexes appear to be much more stable than the sulfur-bound nickel ones.

Metal binding ability of cysteine-rich peptide domain of ZIP13 Zn2+ ions transporter.

The coordination modes and thermodynamic stabilities of the complexes of the cysteine-rich N-terminal domain fragment of the ZIP13 zinc transporter (MPGCPCPGCG-NH(2)) with Zn(2+), Cd(2+), Bi(3+), and Ni(2+) have been studied by potentiometric, mass spectrometric, NMR, CD, and UV-vis spectroscopic methods. All of the studied metals had similar binding modes, with the three thiol sulfurs of cysteine residues involved in metal ion coordination. The stability of the complexes formed in solution changes in the series Bi(3+) ≫ Cd(2+) > Zn(2+) > Ni(2+), the strongest being for bismuth and the weakest for nickel.

The role of His-50 of α-synuclein in binding Cu(II): pH dependence, speciation, thermodynamics and structure.

Copper interaction with alpha synuclein (αS) has been shown to accelerate aggregation and oligomerization of the protein. Three different αS copper binding domains have been proposed: (i) the N-terminal residues (1-9) that represent the minimal copper binding domain; (ii) the His-50 imidazole and (iii) the Asp and Glu residues within the acidic C-terminal domain. The copper coordination at the N-terminus has been extensively characterized and it is generally accepted that it provides the highest affinity site.

Prion proteins and copper ions. Biological and chemical controversies.

The Prion protein (PrP(c)) involvement in some neurodegenerative diseases is well assessed although its "normal" biological role is not completely understood. It is known that PrP(C) can bind Cu(II) ions with high specificity but the order of magnitude of the corresponding affinity constant(s) is still highly debated. This perspective is an attempt to collect the current knowledge on these topics and to build up a bridge between the biological and the chemical points of view.

Design of thiolate rich metal binding sites within a peptidic framework.

A de novo protein design strategy provides a powerful tool to elucidate how heavy metals interact with proteins.Cysteine derivatives of the TRI peptide family (Ac-G(LKALEEK)4G-NH2) have been shown to bind heavy metals in an unusual trigonal geometry. Our present objective was to design binding sites in R-helical scaffolds that are able to form higher coordination number complexes with Cd(II) and Hg(II).

Impact of potential blockers on Ru(III) complex binding to human serum albumin.

The effects of aspirin, vitamin B(12) and warfarin as potential blockers of the ruthenium binding sites in HSA were investigated through UV/visible, circular dichroism (CD), fluorescence spectroscopy and the inductively coupled plasma-atomic emission spectroscopy ICP(AES). The studies on the interactions of several biologically relevant molecules with HSA have shown that drugs like aspirin or warfarin may strongly influence the interaction of serum protein with anticancer drugs. It can derive from the influence of the drug on protein conformation or binding close to binding site of anticancer drug.

Human serum albumin: spectroscopic studies of the paclitaxel binding and proximity relationships with cisplatin and adriamycin.

The interactions of anti-cancer drugs with blood constituents, particularly with serum albumin (HSA) may have a major influence on drug pharmacology and efficacy. In the present work the binding of paclitaxel (trade name Taxol) to human serum albumin and its effect on cisplatin and adriamycin interactions has been investigated through UV/visible, CD, fluorescence spectroscopy and the inductively couplet plasma atomic emission spectroscopy method. Displacement studies with use of bilirubin, as a competitive agent provided relevant information about the location of the binding site in HSA as well as the possible multidrug interactions.

Identification of a novel high affinity copper binding site in the APP(145-155) fragment of amyloid precursor protein.

The copper(II) binding features of the APP(145-155) and APP(145-157) fragments of the amyloid precursor protein, Ac-Glu-Thr-His-Leu-His-Trp-His-Thr-Val-Ala-Lys-NH2 and Ac-Glu-Thr-His-Leu-His-Trp-His-Thr-Val-Ala-Lys-Glu-Thr-NH2 were studied by NMR spectroscopy and NMR findings were supported by UV-vis, CD and EPR spectra. Potentiometric measurements were performed only for the more soluble Ac-Glu-Thr-His-Leu-His-Trp-His-Thr-Val-Ala-Lys-Glu-Thr-NH2 peptide fragment. The following was shown: (i) the imidazole rings of all the three His residues are involved in metal coordination; (ii) metal binding induces ionisation of Leu-148 and His-149 amide nitrogens that complete the donor set to copper(II) in the species dominant at neutral pH; (iii) the unusual coordination scheme of the His-Xxx-His-Xxx-His consensus sequence justifies the high specificity for Cu(II) when compared to SOD-like or albumin-like peptides or even in amyloid Abeta fragments.

The dimeric and tetrameric octarepeat fragments of prion protein behave differently to its monomeric unit.

Potentiometric and spectroscopic data have shown that octarepeat dimer and tetramer are much more effective ligands for Cu(II) ions than simple octapeptide. Thus, the whole N-terminal segment of prion protein due to cooperative effects, could be more effective in binding of Cu(II) than simple peptides containing a His residue. The gain of the Cu(II) binding by longer octarepeat peptides derives from the involvement of up to four imidazoles in the coordination of the first Cu(II) ion.

Interactions of Cu2+ ions with chicken prion tandem repeats.

The potentiometric and spectroscopic (EPR, UV-Vis, CD) data have shown that the chicken prion hexa-repeat (Ac-His-Asn-Pro-Gly-Tyr-Pro-NH(2)) is a very specific ligand for Cu(2+) ions. The His imidazole is an anchoring binding site, then the adjacent amide nitrogen coordinates as a second donor. The presence of Pro at position 3 induces binding of phenolate oxygen as a third donor atom.

Copper binding to the neurotoxic peptide PrP106-126: thermodynamic and structural studies.

The human prion protein fragment PrP(106-126) is a highly fibrillogenic peptide, resistant to proteinases and toxic to neurons; it derives from the normal prion protein (PrP(C)), with which it can interact, thus inhibiting its superoxide dismutase-like activity. The same properties are also shown by the abnormal isoform of the prion protein (PrP(Sc)), and this similarity makes PrP(106-126) an interesting model for the neurotoxic action of PrP(Sc). A role for copper in PrP(106-126) aggregation and toxicity has recently been evidenced, and the interaction of terminal Lys, His and Met residues with the copper ion at neutral pH has been suggested.

Binding abilities of dehydropeptides towards Cu(II) and Ni(II) ions. Impact of Z-E isomerization on metal ion binding.

The study on the binding ability of dehydro-tri- and tetrapeptides has shown that the alpha,beta-double bond has a critical effect on the peptide coordination to metal ions. It may affect the binding of the vicinal amide nitrogens by the electronic effect and stabilize the complex due to steric effects. The (Z) isomer is the most effective in stabilizing of the complexes formed.