Cardiolipin interactions with cytochrome c increase tyrosine nitration yields and site-specificity

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.

Interplay of carbon dioxide and peroxide metabolism in mammalian cells

The carbon dioxide/bicarbonate (CO₂/HCO₃^-) molecular pair is ubiquitous in mammalian cells and tissues, mainly as a result of oxidative decarboxylation reactions that occur during intermediary metabolism. CO₂ is in rapid equilibrium with HCO₃^-via the hydration reaction catalyzed by carbonic anhydrases. Far from being an inert compound in redox biology, CO₂ enhances or redirects the reactivity of peroxides, modulating the velocity, extent, and type of one- and two-electron oxidation reactions mediated by hydrogen peroxide (H₂O₂) and peroxynitrite (ONOO^-/ONOOH). Herein, we review the biochemical mechanisms by which CO₂ engages in peroxide-dependent reactions, free radical production, redox signaling, and oxidative damage. First, we cover the metabolic formation of CO₂ and its connection to peroxide formation and decomposition. Next, the reaction mechanisms, kinetics, and processes by which the CO₂/peroxide interplay modulates mammalian cell redox biology are scrutinized in-depth. Importantly, CO₂ also regulates gene expression related to redox and nitric oxide metabolism and as such influences oxidative and inflammatory processes. Accumulated biochemical evidence in vitro, in cellula, and in vivo unambiguously show that the CO₂ and peroxide metabolic pathways are intertwined and together participate in key redox events in mammalian cells.

Tetrahydrobiopterin in Cell Function and Death Mechanisms

Significance: Tetrahydrobiopterin (BH4) is most well known as a required cofactor for enzymes regulating cellular redox homeostasis, aromatic amino acid metabolism, and neurotransmitter synthesis. Less well known are the effects dependent on the cofactor's availability, factors governing its synthesis and recycling, redox implications of the cofactor itself, and protein-protein interactions that underlie cell death. This review provides an understanding of the recent advances implicating BH4 in the mechanisms of cell death and suggestions of possible therapeutic interventions. Recent Advances: The levels of BH4 often reflect the sum of synthetic and recycling enzyme activities. Enhanced expression of GTP cyclohydrolase, the rate-limiting enzyme in biosynthesis, increases BH4, leading to improved cell function and survival. Pharmacologically increasing BH4 levels has similar beneficial effects, leading to enhanced production of neurotransmitters and nitric oxide or reducing oxidant levels. The GTP cyclohydrolase-BH4 pairing has been implicated in a type of cell death, ferroptosis. At the cellular level, BH4 counteracts anticancer therapies directed to enhance ferroptosis via glutathione peroxidase 4 (GPX4) activity inhibition. Critical Issues: Because of the multitude of intertwined mechanisms, a clear relationship between BH4 and cell death is not well understood yet. The possibility that the cofactor directly influences cell viability has not been excluded in previous studies when modulating BH4-producing enzymes. Future Directions: The importance of cellular BH4 variations and BH4 biosynthetic enzymes to cell function and viability makes it essential to better characterize temporal changes, cofactor activity, and the influence on redox status, which in turn would help develop novel therapies. Antioxid. Redox Signal. 37, 171-183.

In-silico-library-based method enables rapid and comprehensive annotation of cardiolipins and cardiolipin oxidation products using high resolution tandem mass spectrometer

Accumulated evidences suggest that cardiolipins (CLs) and cardiolipin oxidation products (oxCLs) are a class of essential molecules that play critical roles in many physiological functions. Diversity of four acyl chains leads to high structure complexity for cardiolipin species including CLs, monolysocardiolipins (MLCLs) and their oxCLs. The ability to rapidly identify CL species can be implemented by the match of mass spectrometry (MS)-based in-silico spectral database. In this study, after optimizing the chromatography conditions and MS detection, an in-silico library containing 377,754 simulated tandem mass spectra deducing from 31,578 CLs to 52,160 of MLCLs was successfully augmented based on LipidBlast templates. For the construction of the oxCLs' library, twenty-five fatty acyls oxidation products relating to nine oxidation types were permuted and combined. A total of 42,180 oxCL spectra were predicted based on the experimental measurements of oxCLs forming by artificially oxidation. Applying the in-silico database to murine mitochondria and cell samples enabled the sensitive and comprehensive annotation of 86 MLCLs, 307 CLs and 112 oxCLs with high annotation confidence. Compared to the conventional method, our proposed in-silico database provides a more comprehensive interpretation for CL species' characterization with high throughput and sensitivity in nontarget lipidomic study.