Interaction between Proteins and Ir Based CO Releasing Molecules: Mechanism of Adduct Formation and CO Release

Digging into protein metalation differences triggered by fluorine containing-dirhodium tetracarboxylate analogues

Catalytic and biological properties of dirhodium tetracarboxylates ([Rh2(μ-O2CR)4L2], L=axial ligand, R=CH3-, CH3CH2-, etc) largely depend on the nature of the bridging carboxylate equatorial μ-O2CR ligands, which can be easily exchanged...

Recent advances in protein metalation: structural studies

Recent advances in structural studies unveiling the basis of the metal compounds/protein recognition process are discussed.

Antimicrobial properties of half-sandwich Ir(iii) cyclopentadienyl complexes with pyridylbenzimidazole ligands

Ethyl group determined the toxicity of pyridylbenzimidazole Ir(iii) compounds and exchange of the group with sulfonate led to diminishing of the antibacterial activity. Increasing the metal content per complex, 3, gave rise to a compound with no toxicity.

Investigating in Vitro Amyloid Peptide 1-42 Aggregation: Impact of Higher Molecular Weight Stable Adducts

The self-assembly of amyloid peptides (Aβ), in particular Aβ_1-42, into oligomers and fibrils is one of the main pathological events related to Alzheimer's disease. Recent studies have demonstrated the ability of carbon monoxide-releasing molecules (CORMs) to protect neurons and astrocytes from Aβ_1-42 toxicity. In fact, CORMs are able to carry and release controlled levels of CO and are known to exert a wide range of anti-inflammatory and anti-apoptotic activities at physiologically relevant concentrations. In order to investigate the direct effects of CORMs on Aβ_1-42, we studied the reactivity of CORM-2 and CORM-3 with Aβ_1-42 in vitro and the potential inhibition of its aggregation by mass spectrometry (MS), as well as fluorescence and circular dichroism spectroscopies. The application of an electrospray ionization-MS (ESI-MS) method allowed the detection of stable Aβ_1-42/CORMs adducts, involving the addition of the Ru(CO)₂ portion of CORMs at histidine residues on the Aβ_1-42 skeleton. Moreover, CORMs showed anti-aggregating properties through formation of stable adducts with Aβ_1-42 as demonstrated by a thioflavin T fluorescence assay and MS analysis. As further proof, comparison of the CD spectra of Aβ_1-42 recorded in the absence and in the presence of CORM-3 at a 1:1 molar ratio showed the ability of CORM-3 to stabilize the peptide in its soluble, unordered conformation, thereby preventing its misfolding and aggregation. This multi-methodological investigation revealed novel interactions between Aβ_1-42 and CORMs, contributing new insights into the proposed neuroprotective mechanisms mediated by CORMs and disclosing a new strategy to divert amyloid aggregation and toxicity.

On the pH-Modulated Ru-Based Prodrug Activation Mechanism

The Ru^III-based prodrug AziRu efficiently binds to proteins, but the mechanism of its release is still disputed. Herein, in order to test the hypothesis of a reduction-mediated Ru release from proteins, a Raman-assisted crystallographic study on AziRu binding to a model protein (hen egg white lysozyme), in two different oxidation states, Ru^II and Ru^III, was carried out. Our results indicate Ru reduction, but the Ru release upon reduction is dependent on the reducing agent. To better understand this process, a pH-dependent, spectroelectrochemical surface-enhanced Raman scattering (SERS) study was performed also on AziRu-functionalized Au electrodes as a surrogate and simplest model system of Ru^II- and Ru^III-based drugs. This SERS study provided a p K_a of 6.0 ± 0.4 for aquated AziRu in the Ru^III state, which falls in the watershed range of pH values separating most cancer environments from their physiological counterparts. These experiments also indicate a dramatic shift of the redox potential E₀ by >600 mV of aquated AziRu toward more positive potentials upon acidification, suggesting a selective AziRu reduction in cancer lumen but not in healthy ones. It is expected that the nature of the ligands (e.g., pyridine vs imidazole, present in well-known Ru^III complex NAMI-A) will modulate the p K_a and E₀, without affecting the underlying reaction mechanism.

Principles and methods used to grow and optimize crystals of protein-metallodrug adducts, to determine metal binding sites and to assign metal ligands

The characterization of the interactions between biological macromolecules (proteins and nucleic acids) and metal-based drugs is a fundamental prerequisite for understanding their mechanisms of action. X-ray crystallography enables the structural analysis of such complexes with atomic level detail. However, this approach requires the preparation of highly diffracting single crystals, the measurement of diffraction patterns and the structural analysis and interpretation of macromolecule-metal interactions from electron density maps. In this review, we describe principles and methods used to grow and optimize crystals of protein-metallodrug adducts, to determine metal binding sites and to assign and validate metal ligands. Examples from the literature and experience in our own laboratory are provided and key challenges are described, notably crystallization and molecular model refinement against the X-ray diffraction data.

Raman-markers of X-ray radiation damage of proteins

Despite their high relevance, the mechanisms of X-ray radiation damage on protein structure yet have to be completely established. Here, we used Raman microspectrophotometry to follow X-ray-induced chemical modifications on the structure of the model protein bovine pancreatic ribonuclease (RNase A). The combination of dose-dependent Raman spectra and ultrahigh resolution (eight structures solved using data collected between 0.85 and 1.17 Å resolution on the same single crystal) allowed direct observation of several radiation damage events, including covalent bond breakages and formation of radicals. Our results are relevant for analytical photodamage detection and provide implications for a detailed understanding of the mechanisms of photoproduct formation.

Enzyme Crystals and Hydrogel Composite Membranes as New Active Food Packaging Material

The great antimicrobial and antioxidant potential of enzymes makes them prone to be used as active packaging materials to preserve food from contamination or degradation. Major drawbacks are connected to the use of enzymes freely dispersed in solution, due to reduced protein stability. The immobilization of enzymes on solid supports to create biocatalytic interfaces has instead been proven to increase their stability and efficiency. In this work, it is shown that enzymes crystallized on hydrogel composite membranes (HCMs) can exert an effective antimicrobial action, thus making the composite membrane and crystals biofilm a potential active substrate for food packaging applications. The antimicrobial hen egg white lysozyme is crystallized on the surface of the hydrogel layer of HCMs, and its activity is determined by measuring the decrease in absorbance of Micrococcus lysodeikticus culture incubated with the specimen. The overall catalytic efficiency of the antimicrobial HCMs increases by a factor of 2 compared to the pure enzyme dissolved in solution at the same quantity. Because the enzyme in crystalline form is present in higher concentration and purity than in the solution, both its overall catalytic efficiency and antimicrobial action increase. Moreover, the hydrogel environment allows a better protein stabilization and retention during crystals dissolution.

Exploring the interactions between model proteins and Pd(ii) or Pt(ii) compounds bearing charged N,N-pyridylbenzimidazole bidentate ligands by X-ray crystallography

X-ray structure of the adducts formed between lysozyme and Pd(ii) and Pt(ii) compounds bearing N,N-pyridylbenzimidazole derivatives with an alkylated sulfonate or phosphonium side chain are reported.

Structural isomerism of Ru(ii)-carbonyl complexes: synthesis, characterization and their antitrypanosomal activities

New complexes with the formula [RuCl(CO)(dppb)(N–N)]PF₆ were prepared by varying the CO position as well as the diimine ligand.

Properties of a flavonol-based photoCORM in aqueous buffered solutions: influence of metal ions, surfactants and proteins on visible light-induced CO release

A flavonol-based photoCORM exhibits reliable visible light-induced CO release in aqueous buffer environments containing constituents of relevance to biological environments.

Ru-Based CO releasing molecules with azole ligands: interaction with proteins and the CO release mechanism disclosed by X-ray crystallography

Structural data on the adducts formed upon reaction of Ru-based CO releasing molecules containing azole ligands with model proteins are reported.

An NMR-Guided Screening Method for Selective Fragment Docking and Synthesis of a Warhead Inhibitor

Selective hits for the glutaredoxin ortholog of Brucella melitensis are determined using STD NMR and verified by trNOE and (15)N-HSQC titration. The most promising hit, RK207, was docked into the target molecule using a scoring function to compare simulated poses to experimental data. After elucidating possible poses, the hit was further optimized into the lead compound by extension with an electrophilic acrylamide warhead. We believe that focusing on selectivity in this early stage of drug discovery will limit cross-reactivity that might occur with the human ortholog as the lead compound is optimized. Kinetics studies revealed that lead compound 5 modified with an ester group results in higher reactivity than an acrylamide control; however, after modification this compound shows little selectivity for bacterial protein versus the human ortholog. In contrast, hydrolysis of compound 5 to the acid form results in a decrease in the activity of the compound. Together these results suggest that more optimization is warranted for this simple chemical scaffold, and opens the door for discovery of drugs targeted against glutaredoxin proteins-a heretofore untapped reservoir for antibiotic agents.

Light- or oxidation-triggered CO release from [MnI(CO)3(κ3-L)] complexes: reaction intermediates and a new synthetic route to [MnIII/IV2(μ-O)2(L)2] compounds

The substitution of the carbonyl ligands of [Mn^I(CO)₃(κ³-L)] complexes can be triggered in two different ways: by near-UV irradiation or by electrochemical oxidation of Mn^I to Mn^II.

Mapping the protein-binding sites for iridium(iii)-based CO-releasing molecules

Mass spectrometry, Raman microspectroscopy, circular dichroism and X-ray crystallography have been used to investigate the reaction of CO-releasing molecule Cs₂IrCl₅CO with the model protein RNase A.