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The catalytic properties of cytochrome c (C c ) have captured great interest in respect to mitochondrial physiology and apoptosis, and hold potential for novel enzymatic bioremediation systems. Nevertheless, its contribution to the metabolism of environmental toxicants remains unstudied. Human exposure to polycyclic aromatic hydrocarbons (PAHs) has been associated with impactful diseases, and animal models have unveiled concerning signs of PAHs' toxicity to mitochondria. In this work, a series of eight PAHs with ionization potentials between 7.2 and 8.1 eV were used to challenge the catalytic ability of C c and to evaluate the effect of vesicles containing cardiolipin mimicking mitochondrial membranes activating the peroxidase activity of C c . With moderate levels of H 2 O 2 and at pH 7.0, C c catalyzed the oxidation of toxic PAHs, such as benzo[a]pyrene, anthracene, and benzo[a]anthracene, and the cardiolipin-containing membranes clearly increased the PAH conversions. Our results also demonstrate for the first time that C c and C c -cardiolipin complexes efficiently transformed the PAH metabolites 2-hydroxynaphthalene and 1-hydroxypyrene. In comparison to horseradish peroxidase, C c was shown to reach more potent oxidizing states and react with PAHs with ionization potentials up to 7.70 eV, including pyrene and acenaphthene. Spectral assays indicated that anthracene binds to C c , and docking simulations proposed possible binding sites positioning anthracene for oxidation. The results give support to the participation of C c in the metabolism of PAHs, especially in mitochondria, and encourage further investigation of the molecular interaction between PAHs and C c .

Lipid membrane nanodomains or lipid rafts are 10-200 nm diameter size cholesterol- and sphingolipid-enriched domains of the plasma membrane, gathering many proteins with different roles. Isolation and characterization of plasma membrane proteins by differential centrifugation and proteomic studies have revealed a remarkable diversity of proteins in these domains. The limited size of the lipid membrane nanodomain challenges the simple possibility that all of them can coexist within the same lipid membrane domain. As caveolin-1, flotillin isoforms and gangliosides are currently used as neuronal lipid membrane nanodomain markers, we first analyzed the structural features of these components forming nanodomains at the plasma membrane since they are relevant for building supramolecular complexes constituted by these molecular signatures. Among the proteins associated with neuronal lipid membrane nanodomains, there are a large number of proteins that play major roles in calcium signaling, such as ionotropic and metabotropic receptors for neurotransmitters, calcium channels, and calcium pumps. This review highlights a large variation between the calcium signaling proteins that have been reported to be associated with isolated caveolin-1 and flotillin-lipid membrane nanodomains. Since these calcium signaling proteins are scattered in different locations of the neuronal plasma membrane, i.e., in presynapses, postsynapses, axonal or dendritic trees, or in the neuronal soma, our analysis suggests that different lipid membrane-domain subtypes should exist in neurons. Furthermore, we conclude that classification of lipid membrane domains by their content in calcium signaling proteins sheds light on the roles of these domains for neuronal activities that are dependent upon the intracellular calcium concentration. Some examples described in this review include the synaptic and metabolic activity, secretion of neurotransmitters and neuromodulators, neuronal excitability (long-term potentiation and long-term depression), axonal and dendritic growth but also neuronal cell survival and death.

Amyloid β (Aβ) oligomers are the most neurotoxic forms of Aβ, and Aβ(1-42) is the prevalent Aβ peptide found in the amyloid plaques of Alzheimer's disease patients. Aβ(25-35) is the shortest peptide that retains the toxicity of Aβ(1-42). Aβ oligomers bind to calmodulin (CaM) and calbindin-D28k with dissociation constants in the nanomolar Aβ(1-42) concentration range. Aβ and histidine-rich proteins have a high affinity for transition metal ions Cu 2+ , Fe 3+ and Zn 2+ . In this work, we show that the fluorescence of Aβ(1-42) HiLyte TM -Fluor555 can be used to monitor hexa-histidine peptide (His 6 ) interaction with Aβ(1-42). The formation of His 6 /Aβ(1-42) complexes is also supported by docking results yielded by the MDockPeP Server. Also, we found that micromolar concentrations of His 6 block the increase in the fluorescence of Aβ(1-42) HiLyte TM -Fluor555 produced by its interaction with the proteins CaM and calbindin-D28k. In addition, we found that the His 6 -tag provides a high-affinity site for the binding of Aβ(1-42) and Aβ(25-35) peptides to the human recombinant cytochrome b 5 reductase, and sensitizes this enzyme to inhibition by these peptides. In conclusion, our results suggest that a His 6 -tag could provide a valuable new tool to experimentally direct the action of neurotoxic Aβ peptides toward selected cellular targets.

Cytochrome b 5 reductase (C b 5 R) is a flavoprotein that participates in the reduction of multiple biological redox partners. Co-localization of this protein with nitric oxide sources has been observed in neurons. In addition, the generation of superoxide anion radical by C b 5 R has been observed. A search for specific inhibitors of C b 5 R to understand the role of this protein in these new functions has been initiated. Previous studies have shown the ability of different flavonoids to inhibit C b 5 R. Anthocyanins are a subgroup of flavonoids responsible for most red and blue colors found in flowers and fruits. Although usually represented by the flavylium cation form, these species are only stable at rather acidic pH values (pH ≤ 1). At higher pH values, the flavylium cation is involved in a dynamic reaction network comprising different neutral species with the potential ability to inhibit the activities of C b 5 R. This study aims to provide insights into the molecular mechanism of interaction between flavonoids and C b 5 R using flavylium salts as dynamic inhibitors. The outcome of this study might lead to the design of improved specific enzyme inhibitors in the future.

Cancer is one of the highest prevalent diseases in humans. The chances of surviving cancer and its prognosis are very dependent on the affected tissue, body location, and stage at which the disease is diagnosed. Researchers and pharmaceutical companies worldwide are pursuing many attempts to look for compounds to treat this malignancy. Most of the current strategies to fight cancer implicate the use of compounds acting on DNA damage checkpoints, non-receptor tyrosine kinases activities, regulators of the hedgehog signaling pathways, and metabolic adaptations placed in cancer. In the last decade, the finding of a lipid peroxidation increase linked to 15-lipoxygenases isoform 1 (15-LOX-1) activity stimulation has been found in specific successful treatments against cancer. This discovery contrasts with the production of other lipid oxidation signatures generated by stimulation of other lipoxygenases such as 5-LOX and 12-LOX, and cyclooxygenase (COX-2) activities, which have been suggested as cancer biomarkers and which inhibitors present anti-tumoral and antiproliferative activities. These findings support the previously proposed role of lipid hydroperoxides and their metabolites as cancer cell mediators. Depletion or promotion of lipid peroxidation is generally related to a specific production source associated with a cancer stage or tissue in which cancer originates. This review highlights the potential therapeutical use of chemical derivatives to stimulate or block specific cellular routes to generate lipid hydroperoxides to treat this disease.