Structural basis of mammalian complex IV inhibition by steroids

Phytosterol organic acid esters: Characterization, anti-inflammatory properties and a delivery strategy to improve mitochondrial function

Phytosterol organic acid esters are important food resources and the components of biomembrane structure. Due to the lack of extraction and synthesis techniques, more research has been focused on phytosterols, and the research on phytosterol acid esters have encountered a bottleneck, but phytosterol acid esters confer substantial benefits to human health. In this study, stigmasteryl vanillate (VAN), stigmasteryl protocatechuate (PRO) and stigmasteryl sinapate (SIN) were prepared through the Steglich reaction. The processes are promotable and the products reach up to 95% purity. In addition, their stability was evaluated by differential scanning calorimetry and thermogravimetric analysis. HPLC analysis revealed an enhancement in water solubility after esterification with phenolic acid. In an in vitro digestion model, the bioaccessibility of stigmasteryl phenolates was significantly higher than that of stigmasterols (STIs). Regarding the anti-inflammatory properties, VAN, PRO, and SIN exhibit superior effects against TNF-α induced pro-inflammatory responses compared to STI. All stigmasteryl phenolates supplementation increased the ATP production, the basal, and maximal oxygen consumption rate in mitochondrial stress test. Overall, we present a synthesis method for stigmasteryl phenolates. It will contribute to the development and research of phytosterol acid ester analysis, functions and utilization in food. Moreover, the nutrient-stigmasterol hybrids tactic we have constructed is practical and can become a targeted mitochondrial delivery strategy with enhanced anti-inflammatory effects.

The catalytic reaction of cytochrome c oxidase probed by in situ gas titrations and FTIR difference spectroscopy

Cytochrome c oxidase (CcO) is a transmembrane heme‑copper metalloenzyme that catalyzes the reduction of O2 to H2O at the reducing end of the respiratory electron transport chain. To understand this reaction, we followed the conversion of CcO from Rhodobacter sphaeroides between several active-ready and carbon monoxide-inhibited states via attenuated total reflection Fourier-transform infrared (ATR FTIR) difference spectroscopy. Utilizing a novel gas titration setup, we prepared the mixed-valence, CO-inhibited R2CO state as well as the fully-reduced R4 and R4CO states and induced the "active ready" oxidized state OH. These experiments are performed in the dark yielding FTIR difference spectra exclusively triggered by exposure to O2, the natural substrate of CcO. Our data demonstrate that the presence of CO at heme a3 does not impair the catalytic oxidation of CcO when the cycle starts from the fully-reduced states. Interestingly, when starting from the R2CO state, the release of the CO ligand upon purging with inert gas yield a product that is indistinguishable from photolysis-induced states. The observed changes at heme a3 in the catalytic binuclear center (BNC) result from the loss of CO and are unrelated to electronic excitation upon illumination. Based on our experiments, we re-evaluate the assignment of marker bands that appear in time-resolved photolysis and perfusion-induced experiments on CcO.

Interaction of Terminal Oxidases with Amphipathic Molecules

The review focuses on recent advances regarding the effects of natural and artificial amphipathic compounds on terminal oxidases. Terminal oxidases are fascinating biomolecular devices which couple the oxidation of respiratory substrates with generation of a proton motive force used by the cell for ATP production and other needs. The role of endogenous lipids in the enzyme structure and function is highlighted. The main regularities of the interaction between the most popular detergents and terminal oxidases of various types are described. A hypothesis about the physiological regulation of mitochondrial-type enzymes by lipid-soluble ligands is considered.

Interaction of Amphipathic Peptide from Influenza Virus M1 Protein with Mitochondrial Cytochrome Oxidase

The Bile Acid Binding Site (BABS) of cytochrome oxidase (CcO) binds numerous amphipathic ligands. To determine which of the BABS-lining residues are critical for interaction, we used the peptide P4 and its derivatives A1-A4. P4 is composed of two flexibly bound modified α-helices from the M1 protein of the influenza virus, each containing a cholesterol-recognizing CRAC motif. The effect of the peptides on the activity of CcO was studied in solution and in membranes. The secondary structure of the peptides was examined by molecular dynamics, circular dichroism spectroscopy, and testing the ability to form membrane pores. P4 was found to suppress the oxidase but not the peroxidase activity of solubilized CcO. The K_i(app) is linearly dependent on the dodecyl-maltoside (DM) concentration, indicating that DM and P4 compete in a 1:1 ratio. The true K_i is 3 μM. The deoxycholate-induced increase in K_i(app) points to a competition between P4 and deoxycholate. A1 and A4 inhibit solubilized CcO with K_i(app)~20 μM at 1 mM DM. A2 and A3 hardly inhibit CcO either in solution or in membranes. The mitochondrial membrane-bound CcO retains sensitivity to P4 and A4 but acquires resistance to A1. We associate the inhibitory effect of P4 with its binding to BABS and dysfunction of the proton channel K. Trp residue is critical for inhibition. The resistance of the membrane-bound enzyme to inhibition may be due to the disordered secondary structure of the inhibitory peptide.

Cryo-EM structure and function of S. pombe complex IV with bound respiratory supercomplex factor

Fission yeast Schizosaccharomyces pombe serves as model organism for studying higher eukaryotes. We combined the use of cryo-EM and spectroscopy to investigate the structure and function of affinity purified respiratory complex IV (CIV) from S. pombe. The reaction sequence of the reduced enzyme with O₂ proceeds over a time scale of µs-ms, similar to that of the mammalian CIV. The cryo-EM structure of CIV revealed eleven subunits as well as a bound hypoxia-induced gene 1 (Hig1) domain of respiratory supercomplex factor 2 (Rcf2). These results suggest that binding of Rcf2 does not require the presence of a CIII-CIV supercomplex, i.e. Rcf2 is a component of CIV. An AlphaFold-Multimer model suggests that the Hig1 domains of both Rcf1 and Rcf2 bind at the same site of CIV suggesting that their binding is mutually exclusive. Furthermore, the differential functional effect of Rcf1 or Rcf2 is presumably caused by interactions of CIV with their different non-Hig1 domain parts.