Cytochrome c Interaction with Cardiolipin Plays a Key Role in Cell Apoptosis: Implications for Human Diseases

Human cytochrome C natural variants: Studying the membrane binding properties of G41S and Y48H by fluorescence energy transfer and molecular dynamics

Cytochrome C (cyt C), the protein involved in oxidative phosphorylation, plays several other crucial roles necessary for both cell life and death. Studying natural variants of cyt C offers the possibility to better characterize the structure-to-function relationship that modulates the different activities of this protein. Naturally mutations in human cyt C (G41S and Y48H) occur in the protein central Ω-loop and cause thrombocytopenia 4. In this study, we have investigated the binding of such variants and of wild type (wt) cyt C to synthetic cardiolipin-containing vesicles. The mutants have a lower propensity in membrane binding, displaying higher dissociation constants with respect to the wt protein. Compressibility measurements reveal that both variants are more flexible than the wt, suggesting that the native central Ω-loop is important for the interaction with membranes. Such hypothesis is supported by molecular dynamics simulations. A minimal distance analysis indicates that in the presence of cardiolipin the central Ω-loop of the mutants is no more in contact with the membrane, as it happens instead in the case of wt cyt C. Such finding might provide a hint for the reduced membrane binding capacity of the variants and their enhanced peroxidase activity in vivo.

The role of cardiolipin and cytochrome c in mitochondrial metabolism of cancer cells determined by Raman imaging: in vitro study on the brain glioblastoma U-87 MG cell line

In this paper, we present Raman imaging as a non-invasive approach for studying changes in mitochondrial metabolism caused by cardiolipin-cytochrome c interactions. We investigated the effect of mitochondrial dysregulation on cardiolipin (CL) and cytochrome c (Cyt c) interactions for a brain cancer cell line (U-87 MG). Mitochondrial metabolism was monitored by checking the intensities of the Raman bands at 750 cm-1, 1126 cm-1, 1310 cm-1, 1337 cm-1, 1444 cm-1 and 1584 cm-1. The presented results indicate that under pathological conditions, the content and redox status of Cyt c in mitochondria can be used as a Raman marker to characterize changes in cellular metabolism. This work provides evidence that cardiolipin-cytochrome c interactions are crucial for mitochondrial energy homeostasis by controlling the redox status of Cyt c in the electron transport chain, switching from disabling Cyt c reduction and enabling peroxidase activity. This paper provides experimental support for the hypothesis of how cardiolipin-cytochrome c interactions regulate electron transfer in the respiratory chain, apoptosis and mROS production in mitochondria.

Effects of removal of the axial methionine heme ligand on the binding of S. cerevisiae iso-1 cytochrome c to cardiolipin

The cleavage of the axial S(Met) - Fe bond in cytochrome c (cytc) upon binding to cardiolipin (CL), a glycerophospholipid of the inner mitochondrial membrane, is one of the key molecular changes that impart cytc with (lipo)peroxidase activity essential to its pro-apoptotic function. In this work, UV - VIS, CD, MCD and fluorescence spectroscopies were used to address the role of the Fe - M80 bond in controlling the cytc-CL interaction, by studying the binding of the Met80Ala (M80A) variant of S. cerevisiae iso-1 cytc (ycc) to CL liposomes in comparison with the wt protein [Paradisi et al. J. Biol. Inorg. Chem. 25 (2020) 467-487]. The results show that the integrity of the six-coordinate heme center along with the distal heme site containing the Met80 ligand is a not requisite for cytc binding to CL. Indeed, deletion of the Fe - S(Met80) bond has a little impact on the mechanism of ycc-CL interaction, although it results in an increased heme accessibility to solvent and a reduced structural stability of the protein. In particular, M80A features a slightly tighter binding to CL at low CL/cytc ratios compared to wt ycc, possibly due to the lift of some constraints to the insertion of the CL acyl chains into the protein hydrophobic core. M80A binding to CL maintains the dependence on the CL-to-cytc mixing scheme displayed by the wt species.

Effect of COVID-19 mRNA Vaccine on Human Lung Carcinoma Cells In Vitro by Means of Raman Spectroscopy and Imaging

The effect of COVID-19 mRNA vaccine on human lung epithelial carcinoma cells (A549) in vitro as a convenient preclinical model was studied by means of Raman spectroscopy and imaging. The article focuses on Raman imaging as a tool to explore apoptosis and oxidative phosphorylation in mitochondrial dysfunctions. The Raman results demonstrate alterations in the oxidation-reduction pathways associated with cytochrome c. We found that the COVID-19 mRNA vaccine downregulates the concentration of cytochrome c upon incubation with tumorous lung cells. The concentration of the oxidized form of cytochrome c in the mitochondria of lung cells decreases upon incubation with the COVID-19 mRNA vaccine. A lower concentration of oxidized cytochrome c in mitochondria illustrates lower effectiveness of oxidative phosphorylation (respiration), reduced apoptosis, and lessened ATP production. Moreover, mRNA vaccine significantly increases de novo lipids synthesis in lipid droplets up to 96 h and alterations in biochemical composition. It seems that the lipid composition of cells returns to the normal level for a longer incubation time (14 days). In the cell nucleus, the mRNA vaccine does not produce statistically significant changes.

Mutant Cytochrome C as a Potential Detector of Superoxide Generation: Effect of Mutations on the Function and Properties

Cytochrome c (CytC) is a single-electron carrier between complex bc1 and cytochrome c-oxidase (CcO) in the electron transport chain (ETC). It is also known as a good radical scavenger but its participation in electron flow through the ETC makes it impossible to use CytC as a radical sensor. To solve this problem, a series of mutants were constructed with substitutions of Lys residues in the universal binding site (UBS) which interact electrostatically with negatively charged Asp and Glu residues at the binding sites of CytC partners, bc1 complex and CcO. The aim of this study was to select a mutant that had lost its function as an electron carrier in the ETC, retaining the structure and ability to quench radicals. It was shown that a mutant CytC with substitutions of five (8Mut) and four (5Mut) Lys residues in the UBS was almost inactive toward CcO. However, all mutant proteins kept their antioxidant activity sufficiently with respect to the superoxide radical. Mutations shifted the dipole moment of the CytC molecule due to seriously changed electrostatics on the surface of the protein. In addition, a decrease in the redox potential of the protein as revealed by the redox titrations of 8Mut was detected. Nevertheless, the CD spectrum and dynamic light scattering suggested no significant changes in the secondary structure or aggregation of the molecules of CytC 8Mut. Thus, a variant 8Mut with multiple mutations in the UBS which lost its ability to electron transfer and saved most of its physico-chemical properties can be effectively used as a detector of superoxide generation both in mitochondria and in other systems.

Mitochondria Have Made a Long Evolutionary Path from Ancient Bacteria Immigrants within Eukaryotic Cells to Essential Cellular Hosts and Key Players in Human Health and Disease

Mitochondria have made a long evolutionary path from ancient bacteria immigrants within the eukaryotic cell to become key players for the cell, assuming crucial multitasking skills critical for human health and disease. Traditionally identified as the powerhouses of eukaryotic cells due to their central role in energy metabolism, these chemiosmotic machines that synthesize ATP are known as the only maternally inherited organelles with their own genome, where mutations can cause diseases, opening up the field of mitochondrial medicine. More recently, the omics era has highlighted mitochondria as biosynthetic and signaling organelles influencing the behaviors of cells and organisms, making mitochondria the most studied organelles in the biomedical sciences. In this review, we will especially focus on certain 'novelties' in mitochondrial biology "left in the shadows" because, although they have been discovered for some time, they are still not taken with due consideration. We will focus on certain particularities of these organelles, for example, those relating to their metabolism and energy efficiency. In particular, some of their functions that reflect the type of cell in which they reside will be critically discussed, for example, the role of some carriers that are strictly functional to the typical metabolism of the cell or to the tissue specialization. Furthermore, some diseases in whose pathogenesis, surprisingly, mitochondria are involved will be mentioned.

Ligand-Based Regulation of Dynamics and Reactivity of Hemoproteins

Hemoproteins include several heme-binding proteins with distinct structure and function. The presence of the heme group confers specific reactivity and spectroscopic properties to hemoproteins. In this review, we provide an overview of five families of hemoproteins in terms of dynamics and reactivity. First, we describe how ligands modulate cooperativity and reactivity in globins, such as myoglobin and hemoglobin. Second, we move on to another family of hemoproteins devoted to electron transport, such as cytochromes. Later, we consider heme-based reactivity in hemopexin, the main heme-scavenging protein. Then, we focus on heme-albumin, a chronosteric hemoprotein with peculiar spectroscopic and enzymatic properties. Eventually, we analyze the reactivity and dynamics of the most recently discovered family of hemoproteins, i.e., nitrobindins.

Novel triphenylphosphonium amphiphilic conjugates of glycerolipid type: synthesis, cytotoxic and antibacterial activity, and targeted cancer cell delivery

This work deals with the creation of new cationic triphenylphosphonium amphiphilic conjugates of glycerolipid type (TPP-conjugates), bearing a pharmacophore terpenoid fragment (abietic acid and betulin) and a fatty acid residue in one hybrid molecule as a new generation of antitumor agents with high activity and selectivity. The TPP-conjugates showed high mitochondriotropy leading to the development of mitochondriotropic delivery systems such as TPP-pharmacosomes and TPP-solid lipid particles. Introducing the betulin fragment into the structure of a TPP-conjugate (compound 10) increases the cytotoxicity 3 times towards tumor cells of prostate adenocarcinoma DU-145 and 4 times towards breast carcinoma MCF-7 compared to TPP-conjugate 4a in the absence of betulin. TPP-hybrid conjugate 10 with two pharmacophore fragments, betulin and oleic acid, has significant cytotoxicity toward a wide range of tumor cells. The lowest IC50 of 10 is 0.3 μM toward HuTu-80. This is at the level of the reference drug doxorubicin. TPP-pharmacosomes (10/PC) increased the cytotoxic effect approximately 3 times toward HuTu-80 cells, providing high selectivity (SI = 480) compared to the normal liver cell line Chang liver.