Zinc Interactions with a Soluble Mutated Rat Amylin to Mimic Whole Human Amylin: An Experimental and Simulation Approach to Understand Stoichiometry, Speciation and Coordination of the Metal Complexes

Zn2+ and Cu2+ Interaction with the Recognition Interface of ACE2 for SARS-CoV-2 Spike Protein

The spike protein (S) of SARS-CoV-2 is able to bind to the human angiotensin-converting enzyme 2 (ACE2) receptor with a much higher affinity compared to other coronaviruses. The binding interface between the ACE2 receptor and the spike protein plays a critical role in the entry mechanism of the SARS-CoV-2 virus. There are specific amino acids involved in the interaction between the S protein and the ACE2 receptor. This specificity is critical for the virus to establish a systemic infection and cause COVID-19 disease. In the ACE2 receptor, the largest number of amino acids playing a crucial role in the mechanism of interaction and recognition with the S protein is located in the C-terminal part, which represents the main binding region between ACE2 and S. This fragment is abundant in coordination residues such as aspartates, glutamates, and histidine that could be targeted by metal ions. Zn²⁺ ions bind to the ACE2 receptor in its catalytic site and modulate its activity, but it could also contribute to the structural stability of the entire protein. The ability of the human ACE2 receptor to coordinate metal ions, such as Zn²⁺, in the same region where it binds to the S protein could have a crucial impact on the mechanism of recognition and interaction of ACE2-S, with consequences on their binding affinity that deserve to be investigated. To test this possibility, this study aims to characterize the coordination ability of Zn²⁺, and also Cu²⁺ for comparison, with selected peptide models of the ACE2 binding interface using spectroscopic and potentiometric techniques.

Zn(II) binding to pramlintide results in a structural kink, fibril formation and antifungal activity

The antimicrobial properties of amylin, a 37-amino acid peptide hormone, co-secreted with insulin from the pancreas, are far less known than its antidiabetic function. We provide insight into the bioinorganic chemistry of amylin analogues, showing that the coordination of zinc(II) enhances the antifungal properties of pramlintide, a non-fibrillating therapeutic analogue of amylin. Zinc binds to the N-terminal amino group and His18 imidazole, inducing a kink in the peptide structure, which, in turn, triggers a fibrillization process of the complex, resulting in an amyloid structure most likely responsible for the disruption of the fungal cell.

Sometimes less is more-the impact of the number of His residues on the stability of Zn(II)-SmtB and BigR4 α-5 domain complexes

The increasing number of antibiotic-resistant pathogens has become one of the major health problems of modern times, including infections caused by Mycobacterium tuberculosis. One of the possible mammalian immune system responses to mycobacterial infection is the increase of the zinc(ii) concentration in phagosomes to a toxic level. The mycobacterial SmtB protein belongs to the family of ArsR/SmtB transcription regulators. In the presence of high concentrations of metals, SmtB dissociates from DNA and activates the expression of metal efflux proteins. In this work, we focus on the α5 zinc(ii) binding domains of SmtB/BigR4 proteins (the latter being the SmtB homolog from non-pathogenic M. smegmatis) and two mutants of BigR4. We will be taking a closer look at the coordination modes and thermodynamic properties of their zinc(ii) complexes. The study points out the specificity of metal-ligand interactions and describes the effect of mutations on the coordination properties of the studied systems. The stabilities of the zinc(ii) complexes were determined by potentiometry. The coordination sites were determined by NMR experiments and DFT calculations. The comparison of complex stabilities reveals that the Zn(ii)-BigR4 species are more stable than the Zn(ii)-SmtB complexes. His mutations strongly affect the stability of the complexes and the coordination modes of the metal ion. Exchanging one of the histidines for alanine causes, surprisingly, an increase in the stability of zinc(ii) complexes with the studied domain. This was confirmed by potentiometric and DFT methods. This work can be considered as a bioinorganic introduction to the discovery of new strategies in M. tuberculosis infection treatment based on zinc(ii)-sensitive mechanisms.

Undercover Toxic Ménage à Trois of Amylin, Copper (II) and Metformin in Human Embryonic Kidney Cells

In recent decades, type 2 diabetes complications have been correlated with amylin aggregation, copper homeostasis and metformin side effects. However, each factor was analyzed separately, and only in some rare cases copper/amylin or copper/metformin complexes were considered. We demonstrate for the first time that binary metformin/amylin and tertiary copper (II)/amylin/metformin complexes of high cellular toxicity are formed and lead to the formation of aggregated multi-level lamellar structures on the cell membrane. Considering the increased concentration of amylin, copper (II) and metformin in kidneys of T2DM patients, our findings on the toxicity of amylin and its adducts may be correlated with diabetic nephropathy development.

Investigation of the effects of two major secretory granules components, insulin and zinc, on human-IAPP amyloid aggregation and membrane damage

Human islet amyloid polypeptide (hIAPP) is a highly amyloidogenic peptide found in pancreatic islets of type-2 diabetes (T2D) patients. Under certain conditions, hIAPP is able to form amyloid fibrils that play a role in the progression of T2D. hIAPP is synthesized in the β-cell of the pancreas and stored in the secretory granules before being released into the extracellular compartment. It has been suggested that natural stabilizing agents, such as insulin or zinc present in the secretory granules with hIAPP could prevent hIAPP fibril formation. The difference in the amino acid sequences of IAPP among species strongly correlates with amyloidogenicity and toxicity. The residue histidine at position 18 is known to be important in modulating the fibril formation, membrane leakage and toxicity. In this study, we have synthesized four analogues of hIAPP (H18R-IAPP, H18K-IAPP, H18A-IAPP and H18E-IAPP) and characterized their aggregation with either insulin or zinc in order to determine the effect of the residue-18 on the insulin-IAPP and zinc-IAPP interactions using a variety of biophysical experiments including thioflavin-T fluorescence, transmission electron microscopy imaging, circular dichroism, and NMR spectroscopy. We show that insulin reduced hIAPP fibril formation both in solution and in the presence of membrane and hIAPP-membrane damage and that the interactions are somewhat mediated by the residue-18. In addition, our results reveal that zinc affects the process of hIAPP fibril formation in solution but not in the presence of membrane. Our results indicate that the nature of the residue-18 is important for zinc binding. Based on this observation, we hypothesize that zinc binds to the residues in the N-terminal region of hIAPP, which is not accessible in the presence of membrane due to its strong interaction with lipids.