bims-resufa 2018-08-12 papers

Issue of 2018–08–12
four papers selected by
Vera Strogolova, Marquette University

J Biol Chem. 2018 Aug 03. pii: jbc.RA118.003123. [Epub ahead of print]

X-ray structural analyses of azide-bound cytochrome c oxidases reveal that the H-pathway is critically important for the proton-pumping activity.

Atsuhiro Shimada, Keita Hatano, Hitomi Tadehara, Naomine Yano, Kyoko Shinzawa-Itoh, Eiki Yamashita, Kazumasa Muramoto, Tomitake Tsukihara, Shinya Yoshikawa.

Cytochrome c oxidase (CcO) is the terminal oxidase of cellular respiration, reducing O2 to water and pumping protons. X-ray structural features have suggested that CcO pumps protons via a mechanism involving electrostatic repulsions between pumping protons in the hydrogen bond network of a proton-conducting pathway (the H-pathway) and net positive charges created upon oxidation of an iron site, heme α (Fe α2+), for reduction of O2 at another iron site, heme α3 (Fe α32+). The protons for pumping are transferred to the hydrogen bond network from the N-side via the water channel of the H-pathway. Back-leakage of protons to the N-side is thought to be blocked by closure of the water channel. To experimentally test this, we examined X-ray structures of the azide-bound, oxidized bovine CcO and found that an azide derivative (N3--Fe α33+, CuB2+-N3-) induces a translational movement of the heme α3 plane. This was accompanied by opening of the water channel, revealing that Fe α3 and the H-pathway are tightly coupled. The channel opening in the oxidized state is likely to induce back-leakage of pumping protons which lowers the proton level in the hydrogen bond network during enzymatic turnover. The proton level decrease weakens the electron affinity of Fe α , if Fe α electrostatically interacts with protons in the hydrogen bond network. The previously reported azide-induced redox-potential decrease in Fe α supports existence of the electrostatic interaction. In summary, our results indicate that the H-pathway is critical for CcO's proton-pumping function.

Keywords: X-ray crystallography; azide; bioenergetics; copper; cytochrome c oxidase (Complex IV); enzyme mechanism; heme; metalloenzyme; mitochondrial membrane potential; proton pump

DOI: https://doi.org/10.1074/jbc.RA118.003123

Cell Physiol Biochem. 2018 Aug 03. 48(4): 1664-1674

Elevated Serum Potassium Concentration Alleviates Cerebral Ischemia-Reperfusion Injury via Mitochondrial Preservation.

Nuo Li, Sina Qin, Lu Xie, Tao Qin, Yegui Yang, Wei Fang, Meng-Hua Chen.

BACKGROUND/AIMS: The anti-apoptotic effect of an increase in the extracellular concentration of potassium ([K+]) has been confirmed in vitro. However, it is not yet known whether elevated serum [K+] exerts a cerebroprotective effect in vivo. In this study, we aimed to explore the effect of elevated serum [K+] in a rat model of middle cerebral artery occlusion and reperfusion (MCAO/R).
METHODS: Rats subjected to 90-min MCAO received 2.5% KCL, 1.25% KCL, or a normal saline solution at a dose of 3.2 mL/kg at the onset of reperfusion. Rats that were subjected to vascular exposure and ligation without MCAO were defined as the Sham group. Serum [K+] was determined using a blood gas analyzer at 1 min after medicine administration. At 24 h post-reperfusion, rat brains were harvested and processed for 2% 2,3,5-triphenyltetrazolium chloride staining, terminal deoxynucleotidyl transferase-mediated 2'-deoxyuridine 5'-triphosphate-biotin nick end labeling staining, detection of caspase-3 and cleaved-caspase-3 by western blotting, detection of reactive oxygen species (ROS) by dihydroethidium staining, and observation of mitochondrial structure by electron microscopy. In addition, malondialdehyde (MDA), adenosine triphosphate (ATP), total superoxide dismutase (T-SOD), cytochrome C oxidase (COX) activity, and mitochondrial permeability transition pore (MPTP) opening were measured using detection kits.
RESULTS: The results showed that elevated serum [K+] decreased cerebral injury and apoptosis, reduced ROS and MDA levels and MPTP opening, increased ATP levels and cytochrome C oxidase activity, and improved mitochondrial ultrastructural changes, although there was no significant difference in T-SOD activity.
CONCLUSION: These findings suggested that elevated serum [K+] could alleviate cerebral ischemia-reperfusion injury and the mechanism may be associated with the preservation of mitochondrial function.

Keywords: Apoptosis; Ischemia-reperfusion injury; Kcl; Mitochondria

DOI: https://doi.org/10.1159/000492289

Metabolism. 2018 Aug 02. pii: S0026-0495(18)30168-9. [Epub ahead of print]

Sugar or fat: the metabolic choice of the trained heart.

Rita Ferreira, Rita Nogueira-Ferreira, Fábio Trindade, Rui Vitorino, Scott K Powers, Daniel Moreira-Gonçalves.

Mammals respond to muscular exercise by increasing cardiac output to meet the increased demand for oxygen in the working muscles and it is well-established that regular bouts of exercise results in myocardial remodeling. Depending on exercise type, intensity and duration, these cardiac adaptations lead to changes in the energetic substrates required to sustain cardiac contractility. In contrast to the failing heart, fatty acids are the preferred substrate in the trained heart, though glucose metabolism is also enhanced to support oxidative phosphorylation. The participation of AMPK/eNOS and PPARα/PGC-1α pathways in the regulation of cardiac metabolism is well known but other players also contribute including sirtuins and integrins-mediated outside-in activation of FAK and other kinases. These regulatory players act by up-regulating fatty acid uptake, transport to mitochondria and oxidation, and glucose uptake via GLUT4. This exercise-induced increase in mitochondria metabolic flexibility is important to sustain the energetic demand associated with cardiomyocyte hypertrophy and hyperplasia promoted by IGF-1 and neuregulin-1-induced PI3K/Akt signaling. So, the timeless advice of Hippocrates "walking is the best medicine" seems to be justified by the promotion of mitochondrial health and, consequently, the beneficial metabolic remodeling of the heart.

Keywords: Cardiac muscle; Exercise training; Fatty acid oxidation; GLUT4; Metabolic remodeling

DOI: https://doi.org/10.1016/j.metabol.2018.07.004

Trends Plant Sci. 2018 Aug 01. pii: S1360-1385(18)30158-4. [Epub ahead of print]

Iron-Requiring Enzymes in the Spotlight of Oxygen.

Gianpiero Vigani, Irene Murgia.

Iron (Fe) is a cofactor required for a variety of essential redox reactions in plant metabolism. Thus, plants have developed a complex network of interacting pathways to withstand Fe deficiency, including metabolic reprogramming. This opinion aims at revisiting such reprogramming by focusing on: (i) the functional relationships of Fe-requiring enzymes (FeREs) with respect to oxygen; and (ii) the progression of FeREs engagement, occurring under Fe deficiency stress. In particular, we considered such progression of FeREs engagement as strain responses of increasing severity during the stress phases of alarm, resistance, and exhaustion. This approach can contribute to reconcile the variety of experimental results obtained so far from different plant species and/or different Fe supplies.

Keywords: iron deficiency; iron requiring enzymes FeREs; molybdenum; oxygen; plant metabolism

DOI: https://doi.org/10.1016/j.tplants.2018.07.005