Divalent metal ion binding to Staphylococcus aureus FeoB transporter regions

Metal-Induced Amide Deprotonation and Binding Typical for Cu(II), Not Possible for Zn(II) and Fe(II)

Amide groups of the peptide backbone are very weak acids. In fact, their deprotonation in water solution is not a phenomenon usually observed in the measuring range of a glass electrode unless the proton is displaced by a metal such as Cu(II) or Ni(II). Other metals are not usually expected to deprotonate and bind to amide nitrogens, although, lately, some controversies have started to arise in the literature, suggesting that Zn(II) and Fe(II) may be capable of doing so. In order to clarify this phenomenon, we chose to study simple metal-peptide systems with Ala-to-Pro mutations, which excluded further amides from binding. A comparison of the metal-binding modes of Ac-AAAHAAA-NH2, Ac-AAPHAAA-NH2, and Ac-AAPHPAA-NH2 complexes with Cu(II), Zn(II), and Fe(II) is a simple and elegant way of showing that neither Zn(II) nor Fe(II) is able to deprotonate and bind to amide nitrogens.

Systematic Model Peptide Studies: A Crucial Step To Understand the Coordination Chemistry of Mn(II) and Fe(II) in Proteins

Pathogenic bacteria and all other species require Mn(II) and Fe(II) ions for proper growth. Microbes use a variety of assimilation pathways to obtain the necessary metal ions, and their metal homeostasis mechanisms are still not fully uncovered. The knowledge of the poorly discovered complexation chemistry of Mn(II) and Fe(II) ions could help us to understand the basis of those processes better. We have designed six model peptides (L1 - Ac-HHHHHH-NH2, L2 - Ac-HHHHHHHHH-NH2, L3 - Ac-HAHAHAHAH-NH2, L4 - Ac-HHAAAAAAAAAHHHH-NH2, L5 - Ac-HDHDHDHDH-NH2, and L6 - Ac-HEHEHEHEH-NH2) inspired by Mn(II) and Fe(II) binding motifs that are prevalent in nature, in order to clarify their coordination preferences. Spectrometric, spectroscopic, and potentiometric techniques were used to determine the thermodynamic and structural properties of the studied systems. All of the investigated ligands possess efficient Mn(II), Fe(II), and Zn(II) binding sites. Complex stability and metal affinity are significantly influenced by the length of the peptide sequences, as well as the location and quantity of coordinating amino acid residues like His, Asp, and Glu.

The Coordination Chemistry of Two Peptidic Models of NFeoB and Core CFeoB Regions of FeoB Protein: Complexes of Fe(II), Mn(II), and Zn(II)

Often necessary for efficient Fe(II) trafficking into bacterial cell, the Feo system is a vital transporter for many pathogenic bacteria and indispensable for proper development and survival in the host organism during infection. In this work, we present the metal-binding characteristics of the peptidic models of two putative Fe(II)-binding sites of E. coliFeoB: L1 (Ac-477IMRGEATPFVMELPVYHVPH496-CONH2) being a fragment of the Core CFeoB region located between the transmembrane helices and L2 (Ac-38VERKEG43-CONH2), which represents the ExxE motif found within the NFeoB domain. With a variety of physicochemical methods, such as potentiometry, mass spectrometry, NMR, and EPR spectroscopy, we have determined the stability constants and metal-binding residues for the complexes of Fe(II), Mn(II), and Zn(II) with two ligands, L1 and L2, acting as models for the Core CFeoB and ExxE motif. We compare their affinities toward the studied metal ions with the previously studied C-terminal part of the protein and discuss a possible role in metal trafficking by the whole protein.

Exploring divalent metal ion coordination. Unraveling binding modes in Staphylococcus aureus MntH fragments

Metal ion coordination is crucial in bacterial metabolism, while divalent metal ions serve as essential cofactors for various enzymes involved in cellular processes. Therefore, bacteria have developed sophisticated regulatory mechanisms to maintain metal homeostasis. These involve protein interactions for metal ion uptake, efflux, intracellular transport, and storage. Staphylococcus aureus, a member of the commensal flora, colonizes the anterior nares and skin harmlessly but can cause severe illness. MntH transporter is responsible for acquiring divalent metal ions necessary for metabolic functions and virulence. It is a 450-amino-acid protein analogous to Nramp1 (Natural Resistance-Associated Macrophage Protein 1) in mammals. Herein, the coordination modes of copper(II), iron(II), and zinc(II) ions with select fragments of the MntH were established employing potentiometry, mass spectrometry, and spectroscopic methods. Four model peptides, MNNKRHSTNE-NH2, Ac-KFDHRSS-NH2, Ac-IMPHNLYLHSSI-NH2, and Ac-YSRHNNEE-NH2, were chosen for their metal-binding capabilities and examined to determine their coordination properties and preferences. Our findings suggest that under physiological pH conditions, the N-terminal fragment of MntH demonstrates the highest thermodynamic stability with copper(II) and iron(II) ions. Furthermore, a comparison with other peptides from the S. aureus FeoB transporter indicates different binding affinities.

Exogenous methionine contributes to reversing the resistance of Streptococcus suis to macrolides

Streptococcus suis (S. suis) has been increasingly recognized as a porcine zoonotic pathogen that threatens the health of both pigs and humans. Multidrug-resistant Streptococcus suis is becoming increasingly prevalent, and novel strategies to treat bacterial infections caused by these organisms are desperately needed. In the present study, an untargeted metabolomics analysis showed that the significant decrease in methionine content and the methionine biosynthetic pathway were significantly affected by the Kyoto Encyclopedia of Genes and Genomes pathway enrichment analysis in drug-resistant S. suis. The addition of L-methionine restored the bactericidal activity of macrolides, doxycycline, and ciprofloxacin on S. suis in vivo and in vitro. Further studies showed that the exogenous addition of methionine affects methionine metabolism by reducing S-adenosylmethionine synthetase activity and the contents of S-adenosylmethionine, S-adenosyl homocysteine, and S-ribose homocysteine. Methionine can decrease the total methylation level and methylesterase activity in multidrug resistant S. suis. The drug transport proteins and efflux pump genes were significantly downregulated in S. suis by exogenous L-methionine. Moreover, the exogenous addition of methionine can reduce the survival of S. suis by affecting oxidative stress and metal starvation in bacteria. Thus, L-methionine may influence the development of resistance in S. suis through methyl metabolism and metal starvation. This study provides a new perspective on the mitigation of drug resistance in S. suis.IMPORTANCEBacterial antibiotic resistance has become a severe threat to human and animal health. Increasing the efficacy of existing antibiotics is a promising strategy against antibiotic resistance. Here, we report that L-methionine enhances the efficacy of macrolides, doxycycline, and ciprofloxacin antibiotics in killing Streptococcus suis, including multidrug-resistant pathogens. We investigated the mechanism of action of exogenous methionine supplementation in restoring macrolides in Streptococcus suis and the role of the methionine cycle pathway on methylation levels, efflux pump genes, oxidative stress, and metal starvation in Streptococcus suis. It provides a theoretical basis for the rational use of macrolides in clinical practice and also identifies a possible target for restoring drug resistance in Streptococcus suis.

The application of synthetic antibacterial minerals to combat topical infections: exploring a mouse model of MRSA infection

The development of new antibiotics has stalled, and novel strategies are needed as we enter the age of antibiotic resistance. Certain naturally occurring clays have been shown to be effective in killing antibiotic resistant bacteria. However, these natural clays are too variable to be used in clinical settings. Our study shows that synthetic antibacterial minerals exhibit potent antibacterial activity against topical MRSA infections and increase the rate of wound closure relative to controls. The antibacterial minerals maintain a redox cycle between Fe2+/Fe3+ and the surfaces of pyrite minerals, which act as a semiconductor and produce reactive oxygen species (ROS), while smectite minerals act as a cation exchange reservoir. Acidic conditions are maintained throughout the application of the hydrated minerals and can mitigate the alkaline pH conditions observed in chronic non-healing wounds. These results provide evidence for the strategy of 'iron overload' to combat antibiotic resistant infections through the maintained release of Fe2+ and generation of ROS via distinct geochemical reactions that can break the chronic wound damage cycle.

Fe(II), Mn(II), and Zn(II) Binding to the C-Terminal Region of FeoB Protein: An Insight into the Coordination Chemistry and Specificity of the Escherichia coli Fe(II) Transporter

The interactions between two peptide ligands [Ac763CCAASTTGDCH773 (P1) and Ac743RRARSRVDIELLATRKSVSSCCAASTTGDCH773 (P2)] derived from the cytoplasmic C-terminal region of Eschericha coli FeoB protein and Fe(II), Mn(II), and Zn(II) ions were investigated. The Feo system is regarded as the most important bacterial Fe(II) acquisition system, being one of the key virulence factors, especially in anaerobic conditions. Located in the inner membrane of Gram-negative bacteria, FeoB protein transports Fe(II) from the periplasm to the cytoplasm. Despite its crucial role in bacterial pathogenicity, the mechanism in which the metal ion is trafficked through the membrane is not yet elucidated. In the gammaproteobacteria class, the cytoplasmic C-terminal part of FeoB contains conserved cysteine, histidine, and glutamic and aspartic acid residues, which could play a vital role in Fe(II) binding in the cytoplasm, receiving the metal ion from the transmembrane helices. In this work, we characterized the complexes formed between the whole cytosolic C-terminal sequence of E. coli FeoB (P2) and its key polycysteine region (P1) with Fe(II), Mn(II), and Zn(II) ions, exploring the specificity of the C-terminal region of FeoB. With the help of a variety of potentiometric, spectroscopic (electron paramagnetic resonance and NMR), and spectrometric (electrospray ionization mass spectrometry) techniques and molecular dynamics, we propose the metal-binding modes of the ligands, compare their affinities toward the metal ions, and discuss the possible physiological role of the C-terminal region of E. coli FeoB.