Probing the role of metal ions on reversible peptide–protein interactions by NMR

This work provides evidence that paramagnetic lanthanide ions constitute ideal probes suitable for investigations of metal effects upon peptide–receptor interactions with the use of NMR methods. Cerium(III) is herein used for assessing metal effects upon the interaction between angiotensin II and a fragment from the AT1Areceptor. Angiotensin II forms a complex with cerium(III) in water while the fCT300–320receptor fragment is poorly affected by cerium(III). However, the addition of the fragment displaces cerium(III) from the complex, thus directly demonstrating the higher affinity of angiotensin II for the receptor and probing the peptide residues involved in receptor binding

Bioinorganic Chemistry of Micronutrients Related to Alzheimer's and Parkinson's Diseases

: Metal ions are fundamental to guarantee the regular physiological activity of the human organism. Similarly, vitamins play a key role in many biological functions of the metabolism, among which are coenzymes, redox mediators, and antioxidants. Due to their importance in the human organism, both metals and vitamins have been extensively studied for their involvement in neurodegenerative diseases (NDs). However, the full potential of the interaction between vitamins and metal ions has not been fully explored by researchers yet, and further investigation on this topic is needed. The aim of this review is to provide an overview of the scientific literature on the implications of vitamins and selected metal ions in two of the most common neurodegenerative diseases, Alzheimer's and Parkinson's disease. Furthermore, vitamin-metal ion interactions are discussed in detail focusing on their bioinorganic chemistry, with the perspective of arousing more interest in this fascinating bioinorganic field

Quantifying the relevance of different mediators in the human immune cell network

Immune cells coordinate their efforts for the correct and efficient functioning of the immune system (IS). Each cell type plays a distinct role and communicates with other cell types through mediators such as cytokines, chemokines and hormones, among others, that are crucial for the functioning of the IS and its fine tuning. Nevertheless, a quantitative analysis of the topological properties of an immunological network involving this complex interchange of mediators among immune cells is still lacking. Here we present a method for quantifying the relevance of different mediators in the immune network, which exploits a definition of centrality based on the concept of efficient communication. The analysis, applied to the human immune system, indicates that its mediators significantly differ in their network relevance. We found that cytokines involved in innate immunity and inflammation and some hormones rank highest in the network, revealing that the most prominent mediators of the IS are molecules involved in these ancestral types of defence mechanisms highly integrated with the adaptive immune response, and at the interplay among the nervous, the endocrine and the immune systems.Comment: 10 pages, 3 figure

A minimalist chemical model of matrix metalloproteinases- Can small peptides mimic the more rigid metal binding sites of proteins?

In order to develop a minimalist chemical model of matrix metalloproteinases (MMPs), we synthesized a pentadecapeptide (Ac-KAHEFGHSLGLDHSK-NH2) corresponding to the catalytic zinc(II) binding site of human MMP-13. The multi-domain structural organization of MMPs fundamentally determines their metal binding affinity, catalytic activity and selectivity. Our potentiometric, UV-VIS, CD, EPR, NMR, ESI-MS and kinetic study are aimed to explore the usefulness of flexible peptides to mimic the more rigid metal binding sites of proteins, to examine the intrinsic metal binding properties of this naked sequence, as well as to contribute the development of a minimalist, peptide-based chemical model of MMPs, including the catalytic properties. Since multiimidazole environment is also characteristic for copper(II), and recently copper(II) containing variants of MMPs have been identified, we also studied the copper(II) complexes of the above peptide. Around pH 6-7 the peptide, similarly to MMPs, offers {3Nim} coordinated binding site for both zinc(II) and copper(II). In the case of copper(II), the formation of amide coordinated species at higher pH ceased the analogy with the copper(II) containing MMP variant. On the other hand, the zinc(II)-peptide system mimics some basic features of the MMP active sites: the main species around pH 7 (ZnH2L) possesses {3Nim,H2O} coordination environment, the deprotonation of the zinc-bound water takes place near to the physiological pH, it forms relatively stable ternary complexes with hydroxamic acids, and the species ZnH2L(OH) and ZnH2L(OH)2 have notable hydrolytic activity between pH 7-9

2D NMR Methods for Structural Delineation of Copper(II) Complexes of Penicillin and Pilocarpine

A method was developed for delineating the structure of paramagnetic metal complexes. The selective disappearance of cross-peaks in proton-carbon shift correlated 2D NMR maps was shown to uniquely depend upon the scalar and/or dipolar interaction between ligand nuclei and the unpaired electron(s), thus providing a means of identifying binding sites. Copper(II) was shown to form metal complexes with both Penicillin (PNC) and Pilocarpine (PLC) and the structure of the two 1:2 complexes in water solution at physiological pH were determined

A Comparative Study between Lycorine and Galantamine Abilities to Interact with AMYLOID β and Reduce In Vitro Neurotoxicity

Galantamine is a natural alkaloid extracted from the Amaryllidaceae plants and is used as the active ingredient of a drug approved for the treatment of the early stages of Alzheimer's disease. It mainly acts as an acetylcholinesterase (AChE) inhibitor, increasing concentrations of the acetylcholine neurotransmitter. Recent cellular studies have also shown the ability of galantamine to protect SH-SY5Y cell lines against amyloid-beta (A beta)-induced toxicity. Such investigations have supported and validated further in-depth studies for understanding the chemical and molecular features associated with galantamine-protective abilities. In addition to galantamine, other natural alkaloids are known to possess AChE inhibitory activity; among them lycorine has been extensively investigated for its antibacterial, anti-inflammatory and antitumoral activities as well. Despite its interesting biological properties, lycorine's neuroprotective functions against A beta-induced damages have not been explored so far. In this research study, the ability of galantamine and lycorine to suppress A beta-induced in vitro neuronal toxicity was evaluated by investigating the chemical interactions of the two alkaloids with A beta peptide. A multi-technique spectroscopic analysis and cellular cytotoxicity assays were applied to obtain new insights on these molecular associations. The comparison between the behaviors exhibited by the two alkaloids indicates that both compounds possess analogue abilities to interact with the amyloidogenic peptide and protect cells

The effect of a membrane-mimicking environment on the interactions of Cu2+ with an amyloidogenic fragment of chicken prion protein

Prion proteins (PrP) from different species have the ability to tightly bind Cu2+ ions

Histidine-Rich C-Terminal Tail of Mycobacterial GroEL1 and Its Copper Complex─The Impact of Point Mutations

The mycobacterial histidine-rich GroEL1 protein differs significantly compared to the well-known methionine/glycine-rich GroEL chaperonin. It was predicted that mycobacterial GroEL1 can play a significant role in the metal homeostasis of Mycobacteria but not, as its analogue, in protein folding. In this paper, we present the properties of the GroEL1 His-rich C-terminus as a ligand for Cu(II) ions. We studied the stoichiometry, stability, and spectroscopic features of copper complexes of the eight model peptides: L1-Ac-DHDHHHGHAH, L2- Ac-DKPAKAEDHDHHHGHAH, and six mutants of L2 in the pH range of 2-11. We revealed the impact of adjacent residues to the His-rich fragment on the complex stability: the presence of Lys and Asp residues significantly increases the stability of the system. The impact of His mutations was also examined: surprisingly, the exchange of each single His to the Gln residue did not disrupt the ability of the ligand to provide three binding sites for Cu(II) ions. Despite the most possible preference of the Cu(II) ion for the His9-His13 residues (Ac-DKPAKAEDHDHHH-) of the model peptide, especially the His11 residue, the study shows that there is not only one possible binding mode for Cu(II). The significance of this phenomenon is very important for the GroEL1 function -if the single mutation occurs naturally, the protein would be still able to interact with the metal ion

Inferences on the Nature of a Cr(V) or Cr(IV) Species Formed by Reduction of Dichromate by a Bovine Liver Homogenate: NMR and Mass-Spectrometric Studies

A low-molecular weight chromium-containing fraction of the material resulting from dichromate reduction by bovine liver homogenate was investigated by NMR and ES-MS. The ES-MS spectrum showed a readily detectable peak at m/z = 786.1. The same molecular weight reasonably agreed with the relatively low diffusion coefficient measured by NMR-DOSY experiments on the main species observed in the 1H NMR spectrum. At least two downfield shifted and broad paramagnetic signals were apparent in the 1H NMR spectrum. Temperature dependence of chemical shift was exploited in order to estimate the diamagnetic shift of the signals in the diamagnetic region of the spectrum. 2D TOCSY, NOESY, COSY and 1H-3C HMQC spectra revealed the presence of aromatic protons (which were assigned as His residues), Gly and some other short chain amino-acids. Combinations of the molecular masses of such components together with acetate (which is present in the solution) and chromium atoms allowed a tentative proposal of a model for the compound