Proteins involved in the ferrous ions transport in gram-negative bacteria

Continuous increase in the number of multidrug-resistant strains forces us to look for drugs with completely new mode of action. One of the bacterial property determining the pathogenicity of these microorganisms is their ability to obtain iron. Because in the living environment of these single-celled individuals, its concentration is much lower than this necessary for their growth. For this reason, bacteria created various type of iron aquisition systems, including the Feo system, which mechanism of Fe2+ ion uptake is not fully understood, and protein from the Hmu family belonging to ABC transporters. The Feo transport system is one of the most common systems that is exclusively responsible for importing Fe2+ ions. It consists of three proteins: FeoA, FeoB and FeoC. FeoB is a transmembrane protein that is believed to play a key role in the mechanism of Fe2+ ion uptake. The other two components are cytoplasmic proteins. Both, FeoA and FeoC, are cytoplasmic proteins resembling the construction of transcription regulators. ABC transporters play an equally important role in maintaining iron homeostasis. These include proteins from Hmu family. HmuUV complex catalyses the import of these ions in hem iron form. The structure of this complex consists of TMD dimer (HmuU) and NBD dimer (HmuV). The HmuU is considered to be a permease - just like the FeoB described earlier while HmuV is the ATP binding protein

Revised Coordination Model and Stability Constants of Cu(II) Complexes of Tris Buffer

2-Amino-2-hydroxymethyl-propane-1,3-diol, or tris(hydroxymethyl)aminomethane (Tris), is probably the most common biochemical buffer used alone or in combination with other buffers because it is stable, unreactive, and compatible with most proteins and other biomolecules. Being nontoxic, it has even found applications in medicine. Tris is known, however, to coordinate transition metal ions, Cu(II) among them. Although often ignored, this feature affects interactions of Cu(II) ions with biomolecules, as Tris is usually used in high molar excess. Therefore, it is important to have precise knowledge on the stoichiometry, stability, and reactivity of cupric Tris complexes. The literature data are incoherent in this respect. We reinvestigated the complex formation in the Tris-Cu(II) system by potentiometry, UV-vis, ESI-MS, and EPR at a broad range of concentrations and ratios. We found, contrary to several previous papers, that the maximum stoichiometry of Tris to Cu(II) is 2 and at neutral pH, dimeric complexes are formed. The apparent affinity of Tris buffer for Cu(II), determined by the competitivity index (CI) approach [Krężel, A.; Wójcik, J.; Maciejczyk, M.; Bal, W. Chem. Commun. 2003, 6, 704-705] at pH 7.4 varies between 2 × 10(6) and 4 × 10(4) M(-1), depending on the Tris and Cu(II) concentrations and molar ratio

Revised Coordination Model and Stability Constants of Cu(II) Complexes of Tris Buffer

2-Amino-2-hydroxymethyl-propane-1,3-diol, or tris­(hydroxymethyl)­aminomethane (Tris), is probably the most common biochemical buffer used alone or in combination with other buffers because it is stable, unreactive, and compatible with most proteins and other biomolecules. Being nontoxic, it has even found applications in medicine. Tris is known, however, to coordinate transition metal ions, Cu­(II) among them. Although often ignored, this feature affects interactions of Cu­(II) ions with biomolecules, as Tris is usually used in high molar excess. Therefore, it is important to have precise knowledge on the stoichiometry, stability, and reactivity of cupric Tris complexes. The literature data are incoherent in this respect. We reinvestigated the complex formation in the Tris–Cu­(II) system by potentiometry, UV–vis, ESI-MS, and EPR at a broad range of concentrations and ratios. We found, contrary to several previous papers, that the maximum stoichiometry of Tris to Cu­(II) is 2 and at neutral pH, dimeric complexes are formed. The apparent affinity of Tris buffer for Cu­(II), determined by the competitivity index (CI) approach [Krężel, A.; Wójcik, J.; Maciejczyk, M.; Bal, W. <i>Chem. Commun.</i> 2003, <i>6</i>, 704–705] at pH 7.4 varies between 2 × 10⁶ and 4 × 10⁴ M^–1, depending on the Tris and Cu­(II) concentrations and molar ratio

CH vs. HC—Promiscuous Metal Sponges in Antimicrobial Peptides and Metallophores

Histidine and cysteine residues, with their imidazole and thiol moieties that deprotonate at approximately physiological pH values, are primary binding sites for Zn(II), Ni(II) and Fe(II) ions and are thus ubiquitous both in peptidic metallophores and in antimicrobial peptides that may use nutritional immunity as a way to limit pathogenicity during infection. We focus on metal complex solution equilibria of model sequences encompassing Cys–His and His–Cys motifs, showing that the position of histidine and cysteine residues in the sequence has a crucial impact on its coordination properties. CH and HC motifs occur as many as 411 times in the antimicrobial peptide database, while similar CC and HH regions are found 348 and 94 times, respectively. Complex stabilities increase in the series Fe(II) &lt; Ni(II) &lt; Zn(II), with Zn(II) complexes dominating at physiological pH, and Ni(II) ones—above pH 9. The stabilities of Zn(II) complexes with Ac-ACHA-NH2 and Ac-AHCA-NH2 are comparable, and a similar tendency is observed for Fe(II), while in the case of Ni(II), the order of Cys and His does matter—complexes in which the metal is anchored on the third Cys (Ac-AHCA-NH2) are thermodynamically stronger than those where Cys is in position two (Ac-ACHA-NH2) at basic pH, at which point amides start to take part in the binding. Cysteine residues are much better Zn(II)-anchoring sites than histidines; Zn(II) clearly prefers the Cys–Cys type of ligands to Cys–His and His–Cys ones. In the case of His- and Cys-containing peptides, non-binding residues may have an impact on the stability of Ni(II) complexes, most likely protecting the central Ni(II) atom from interacting with solvent molecules

Bacterial strategies for the use of metal ions – backstage of coordiantion chemistry

In the Biological Inorganic Chemistry Group we are inspired to better understand metal ions acquisition and homeostasis in pathogenic bacteria, and in this review we present three different approaches to the role of these processes. The growing importance of a full understanding of the iron transport system in pathogens prompted us to study synthetic analogs of siderophores, used as structural probes in the process of iron uptake by microorganisms. The ferrichrome biomimetic analogs allowed efficient Fe(III) chelation under biological conditions and were recognized better by P. putida. than E. coli, suggesting differences in uptake mechanisms. Addition of a fluorescent probe to the compound allowed to track biological fate of studied complexes [1, 2]. Biomimetics of ferrioxamine E revealed their potential as radioactive 68Ga(III)-based probes [3], and studies of Zr(IV) complexes permitted to explain the in vivo behavior of desferrioxamine B as 89Zr(IV) radionuclide carrier [4], as well as design better chelators for this metal ion [5]. One of the possible mammalian immune system responsesto mycobacterial infection is the increase of Zn(II) concentration in phagosomes to a toxic level [6-8]. The mycobacterial SmtB protein is a transcription regulator that in the presence of high concentrations of metals, dissociates from DNA and activates the expression of metal efflux proteins. We focused on α5 Zn(II) binding domains of SmtB/BigR4 proteins [9], looking at the coordination modes and thermodynamics of their Zn(II) and Ni(II) complexes. The study points out the specificity of metal-ligand interactions and the effect of mutations on the coordination properties of studied systems. The project can be considered as an introduction to the new strategies in tuberculosis treatment based on Zn(II)/Ni(II)-sensitive mechanisms. F. nucleatum is an anaerobic bacteria present in the plaque. It leads not only to periodontal diseases but also, angina, purulent inflammation of the lung tissue or reproductive organs [10]. Moreover, F. nucleatum promotes colon cancer growth [11]. This bacteria strain promotes inflammation and tumorigenesis by modulating the tumor immune microenvironment [12, 13]. Microbial pathogens drive tumorigenesis in 15–20% of cancer cases [14]. However, not only microorganisms are considered a major risk factor, but also metal ions play an important role in tumor promotion [15, 16]. Therefore, our primary research goal is to investigate the effect of metal ions coordination on the activity of outer-membrane proteins from F. nucleatum and to answer whether these proteins increase the prooxidative activity of Cu(II) and Fe(II) ions [16-18]

High affinity of copper(II) towards amoxicillin, apramycin and ristomycin. Effect of these complexes on the catalytic activity of HDV ribozyme

Three representatives of the distinct antibiotics groups: amoxicillin, apramycin and ristomycin A were studied regarding their impact on hepatitis D virus (HDV) ribozyme both in the metal-free form and complexed with copper(II) ions. Hence the Cu(II)-ristomycin A complex has been characterized by means of NMR, EPR, CD and UV-visible spectroscopic techniques and its binding pattern has been compared with the coordination modes estimated previously for Cu(II)-amoxicillin and Cu(II)-apramycin complexes. It has thus been found that all three antibiotics bind the Cu(II) ion in a very similar manner, engaging two nitrogen and two oxygen donors into coordination with the square planar symmetry in physiological conditions. All three tested antibiotics were able to inhibit the HDV ribozyme catalysis. However, in the presence of the complexes, the catalytic reactions were almost completely inhibited. It was important therefore to check whether the complexes used in lower concentrations could inhibit the HDV ribozyme catalytic activity, thus creating opportunities for their practical application. It turned out that the complexes used in the concentrations of 50μM influenced the catalysis much less effectively comparing to the 200 micromolar concentration. The kobs values were lower than those observed in the control reaction, in the absence of potential inhibitors: 2-fold for amoxicillin, ristomycin A and 3.3-fold for apramycin, respectively

Zinc(II)—The Overlooked Éminence Grise of Chloroquine’s Fight against COVID-19?

Zn(II) is an inhibitor of SARS-CoV-2&prime;s RNA-dependent RNA polymerase, and chloroquine and hydroxychloroquine are Zn(II) ionophores&ndash;this statement gives a curious mind a lot to think about. We show results of the first clinical trials on chloroquine (CQ) and hydroxychloroquine (HCQ) in the treatment of COVID-19, as well as earlier reports on the anticoronaviral properties of these two compounds and of Zn(II) itself. Other FDA-approved Zn(II) ionophores are given a decent amount of attention and are thought of as possible COVID-19 therapeutics