Cooperation among c-subunits of FoF1-ATP synthase in rotation-coupled proton translocation.

In FoF1-ATP synthase, proton translocation through Fo drives rotation of the c-subunit oligomeric ring relative to the a-subunit. Recent studies suggest that in each step of the rotation, key glutamic acid residues in different c-subunits contribute to proton release to and proton uptake from the a-subunit. However, no studies have demonstrated cooperativity among c-subunits toward FoF1-ATP synthase activity. Here, we addressed this using Bacillus PS3 ATP synthase harboring a c-ring with various combinations of wild-type and cE56D, enabled by genetically fused single-chain c-ring. ATP synthesis and proton pump activities were decreased by a single cE56D mutation and further decreased by double cE56D mutations. Moreover, activity further decreased as the two mutation sites were separated, indicating cooperation among c-subunits. Similar results were obtained for proton transfer-coupled molecular simulations. The simulations revealed that prolonged proton uptake in mutated c-subunits is shared between two c-subunits, explaining the cooperation observed in biochemical assays.

Cells need to be able to store and transfer energy to fuel their various activities. To do this, they produce a small molecule called ATP to carry the energy, which is then released when the ATP is broken down. An enzyme found in plants, animals and bacteria, called F_oF₁ ATP synthase, can both create and use ATP. When it does this, protons, or positive hydrogen ions, are transported across cellular boundaries called membranes. The region of the enzyme that is responsible for pumping the protons contains different parts known as the c-ring and the a-subunit. The movement of protons drives the c-ring to rotate relative to the a-subunit, which leads to producing ATP. Previous research using simulations and the protein structures found there are two or three neighbouring amino acids in the c-ring that face the a-subunit, suggesting that these amino acids act together to drive the rotation. To test this hypothesis, Mitome et al. mutated these amino acids to examine the effect on the enzyme's ability to produce ATP. A single mutation reduced the production of ATP, which decreased even further with mutations in two of the amino acids. The extent of this decrease depended on the distance between the two mutations in the c-ring. Simulations of these changes also found similar results. This indicates there is coordination between different parts of the c-ring to increase the rate of ATP production. This study offers new insights into the molecular processes controlling ATP synthesis and confirms previous theoretical research. This will interest specialists in bioenergetics because it addresses a fundamental biological question with broad impact.

Short-term administration of a new free radical scavenger, edaravone, is more effective than its long-term administration for the treatment of neonatal hypoxic-ischemic encephalopathy.

BACKGROUND AND PURPOSE: Edaravone (3-methyl-1-phenyl-2-pyrazolin-5-one) is a new free radical scavenger that is used for the treatment of adult acute cerebral infarction in Japan. We examined the effect of edaravone on the optimal duration of treatment, the long-term effect on the brain, and the effect on learning and memory disability in a rat model of neonatal hypoxic-ischemic encephalopathy. METHODS: Seven-day-old Wistar rats were subjected to left common carotid artery ligation then 2 hours of hypoxic-ischemic insult or sham operation. Edaravone was administered intraperitoneally (9 mg/kg) after hypoxic-ischemic insult every 24 hours for 2, 5, or 10 consecutive days. The neuroprotective effect of edaravone was evaluated by behavioral test and histological analysis. RESULTS: Two-day treatment with edaravone significantly gave protection to the learning and memory capability, as well as morphological recovery compared with control rats. Five-day treatment showed morphological improvement but no behavioral improvement. In contrast, 10-day treatment did not show either morphological or behavior improvement. CONCLUSIONS: These findings indicate that edaravone is a promising candidate as a treatment of choice for neonatal hypoxic-ischemic encephalopathy, when its use is limited to the acute phase after hypoxia-ischemia.