The Palladium(II) Complex of Aβ4-16 as Suitable Model for Structural Studies of Biorelevant Copper(II) Complexes of N-Truncated Beta-Amyloids

Synthesis and Biological Activities of Some Metal Complexes of Peptides: A Review

Peptides, both natural and synthetic, are well suited for a wide range of purposes and offer versatile applications in different fields such as biocatalysts, injectable hydrogels, tumor treatment, and drug delivery. The research of the better part of the cited papers was conducted using various database platforms such as MetalPDB. The rising prominence of therapeutic peptides encompasses anticancer, antiviral, antimicrobial, and anti-neurodegenerative properties. The metals Na, K, Mg, Ca, Fe, Mn, Co, Cu, Zn, and Mo are ten of the twenty elements that are considered essential for life. Crucial for understanding the biological role of metals is the exploration of metal-bound proteins and peptides. Aside from essential metals, there are other non-essential metals that also interact biologically, exhibiting either therapeutic or toxic effects. Irregularities in metal binding contribute to diseases like Alzheimer's, neurodegenerative disorders, Wilson's, and Menkes disease. Certain metal complexes have potential applications as radiopharmaceuticals. The examination of these complexes was achieved by preforming UV-Vis, IR, EPR, NMR spectroscopy, and X-ray analysis. This summary, although unable to cover all of the studies in the field, offers a review of the ongoing experimentation and is a basis for new ideas, as well as strategies to explore and gain knowledge from the extensive realm of peptide-chelated metals and biotechnologies.

The Cu(II) affinity constant and reactivity of Hepcidin-25, the main iron regulator in human blood

Hepcidin is an iron regulatory hormone that does not bind iron directly. Instead, its mature 25-peptide form (H25) contains a binding site for other metals, the so-called ATCUN/NTS (amino-terminal Cu/Ni binding site). The Cu(II)-hepcidin complex was previously studied, but due to poor solubility and difficult handling of the peptide the definitive account on the binding equilibrium was not obtained reliably. In this study we performed a series of fluorescence competition experiments between H25 and its model peptides containing the same ATCUN/NTS site and determined the Cu(II) conditional binding constant of the CuH25 complex at pH 7.4, CK7.4 = 4 ± 2 × 1014 M-1. This complex was found to be very inert in exchange reactions and poorly reactive in the ascorbate consumption test. The consequences of these findings for the putative role of Cu(II) interactions with H25 are discussed.

Studying Peptide-Metal Ion Complex Structures by Solution-State NMR

Metal chelation can provide structural stability and form reactive centers in metalloproteins. Approximately one third of known protein structures are metalloproteins, and metal binding, or the lack thereof, is often implicated in disease, making it necessary to be able to study these systems in detail. Peptide-metal complexes are both present in nature and can provide a means to focus on the binding region of a protein and control experimental variables to a high degree. Structural studies of peptide complexes with metal ions by nuclear magnetic resonance (NMR) were surveyed for all the essential metal complexes and many non-essential metal complexes. The various methods used to study each metal ion are presented together with examples of recent research. Many of these metal systems have been individually reviewed and this current overview of NMR studies of metallopeptide complexes aims to provide a basis for inspiration from structural studies and methodology applied in the field.

A gliclazide complex based on palladium towards Alzheimer's disease: promising protective activity against Aβ-induced toxicity in C. elegans

A new palladium coordination compound based on gliclazide with the chemical formula [Pd(glz)₂] (where glz = gliclazide) has been synthesized and characterised. The structural characterization reveals that this material consists of mononuclear units formed by a Pd²⁺ ion coordinated to two molecules of the glz ligand, in which palladium ions exhibit a distorted plane-square coordination sphere. This novel material behaves like a good and selective inhibitor of butyrylcholinesterase, one of the most relevant therapeutic targets against Alzheimer's disease. Analysis of the enzyme kinetics showed a mixed mode of inhibition, the title compound being capable of interacting with both the free enzyme and the enzyme-substrate complex. Finally, the palladium compound shows promising protective activity against Aβ-induced toxicity in the Caenorhabditis elegans model, which has never been reported.

Fluorescent Analogues of FRH Peptide: Cu(II) Binding and Interactions with ds-DNA/RNA

Four novel peptidoids, derived from the Phe-Arg-His (FRH) peptide motif, were prepared by replacing the histidine heterocycle with triazole and consequent triazole-fluorophore (coumarin) extension and also replacing arginine with less voluminous lysine. So the constructed Phe-Lys-Ala(triazole) (FKA(triazole)) peptidoids bind Cu2+ cations in water with a strong, nanomolar affinity comparable to the parent FRH and its known analogs, demonstrating that triazole can coordinate copper similarly as histidine. Moreover, even short KA(triazole)coumarin showed submicromolar affinity to Cu2+. Only FKA(triazole)coumarin with free amino groups and its shorter analog KA(triazole)coumarin showed strong induced CD spectra upon Cu2+ cation binding. Thus, KA(triazole)coumarin can be considered as the shortest peptidoid sequence with highly sensitive fluorescent and chiral CD response for Cu2+ cation, encouraging further studies with other metal cations. The FKA(triazole) coumarin peptidoids show biorelevant, 10 µM affinity to ds-DNA and ds-RNA, binding within DNA/RNA grooves. Intriguingly, only peptidoid complexes with Cu2+ strongly stabilize ds-DNA and ds-RNA against thermal denaturation, suggesting significant interactions of Cu2+ cation within the DNA/RNA binding site.