High-resolution cryo-EM structure of photosystem II reveals damage from high-dose electron beams

Photosystem II (PSII) plays a key role in water-splitting and oxygen evolution. X-ray crystallography has revealed its atomic structure and some intermediate structures. However, these structures are in the crystalline state and its final state structure has not been solved. Here we analyzed the structure of PSII in solution at 1.95 Å resolution by single-particle cryo-electron microscopy (cryo-EM). The structure obtained is similar to the crystal structure, but a PsbY subunit was visible in the cryo-EM structure, indicating that it represents its physiological state more closely. Electron beam damage was observed at a high-dose in the regions that were easily affected by redox states, and reducing the beam dosage by reducing frames from 50 to 2 yielded a similar resolution but reduced the damage remarkably. This study will serve as a good indicator for determining damage-free cryo-EM structures of not only PSII but also all biological samples, especially redox-active metalloproteins

Double-Network Hydrogels Strongly Bondable to Bones by Spontaneous Osteogenesis Penetration

Implanting hydroxyapatite-mineralized tough hydrogel into osteochondral defects of rabbits, osteogenesis spontaneously penetrates into the gel matrix owing to the semi-permeablility of the hydrogel. The gradient layer (around 40 μm thick) contributes quite strong bonding of the gel to bone. This is the first success in realizing the robust osteointegration of tough hydrogels, and the method is simple and feasible for practical use

Structural basis for the absence of low-energy chlorophylls in a photosystem I trimer from Gloeobacter violaceus

Photosystem I (PSI) is a multi-subunit pigment-protein complex that functions in light-harvesting and photochemical charge-separation reactions, followed by reduction of NADP to NADPH required for CO2 fixation in photosynthetic organisms. PSI from different photosynthetic organisms has a variety of chlorophylls (Chls), some of which are at lower-energy levels than its reaction center P700, a special pair of Chls, and are called low-energy Chls. However, the sites of low-energy Chls are still under debate. Here, we solved a 2.04-& ANGS; resolution structure of a PSI trimer by cryo-electron microscopy from a primordial cyanobacterium Gloeobacter violaceus PCC 7421, which has no low-energy Chls. The structure shows the absence of some subunits commonly found in other cyanobacteria, confirming the primordial nature of this cyanobacterium. Comparison with the known structures of PSI from other cyanobacteria and eukaryotic organisms reveals that one dimeric and one trimeric Chls are lacking in the Gloeobacter PSI. The dimeric and trimeric Chls are named Low1 and Low2, respectively. Low2 is missing in some cyanobacterial and eukaryotic PSIs, whereas Low1 is absent only in Gloeobacter. These findings provide insights into not only the identity of low-energy Chls in PSI, but also the evolutionary changes of low-energy Chls in oxyphototrophs

Status of 48Ca double beta decay search in CANDLES

We study a strategy to reduce veto-time in the search for neutrino-less double-beta decay (0υββ) with CANDLES-III system. We develop a new likelihood analysis and apply it to our new Run010 data. We show that we can increase the un-vetoed live-time by 11.8%. Thanks to this improvements, We expect to increase a limit on the life-time of 0υββ by a factor of three by analyzing both Run009 and Run010 data

Crack Tip Field of a Double-Network Gel: Visualization of Covalent Bond Scission through Mechanoradical Polymerization

Quantitative characterization of the energy dissipation zone around a crack tip is the focal point in the fracture mechanics of soft materials. In this report, we present a mechanochemical technique for the visualization and quantification of the degree of polymer strand scission in the damage zone of tough double-network hydrogels. This technique uses mechanoradicals generated by covalent bond scission to initiate radical polymerization, which records the internal fracturing around the crack tip during crack opening or propagation. We adopted the mechanoradical polymerization of N-isopropylacrylamide, which forms a thermoresponsive polymer and whose distribution was visualized using an environment-responsive fluorescent probe. Twoand three-dimensional damage distributions were captured using a laser scanning confocal microscope. This technique also allowed for the quantitative estimation of the spatial distribution of stress, strain, and energy dissipation around the crack tip. The advantages and limitations of this technique are also discussed

Double-network gels as polyelectrolyte gels with salt-insensitive swelling properties

Polyelectrolyte gels exhibit intrinsic salt-sensitive swelling behaviour, which causes size instability in ionic environments. Thus, polyelectrolyte gels that show salt-insensitive swelling have been anticipated for applications in ionic environments, such as medical materials usedin vivo. We found that double-network (DN) gels consisting of both a polyelectrolyte network and a non-ionic network are resistant to salt-sensitive swelling. This resistance is attributed to their lower osmotic pressure originating from mobile ions relative to the osmotic pressure of mixing at swelling equilibrium. Our investigation indicated that the two contrasting network structures within the DN gels are vital for achieving these properties, where the structures include a highly prestretched and sparse polyelectrolyte network and a coiled and dense non-ionic network. The salt-insensitivity of the DN gels will lead to their unique applications in ionic environments

Revisiting the Origins of the Fracture Energy of Tough Double-Network Hydrogels with Quantitative Mechanochemical Characterization of the Damage Zone

The high fracture energy of tough soft materials can be attributed to the large energy dissipation zone around the crack tip. Hence, quantitative characterization of energy dissipation is the key to soft matter fracture mechanics. In this study, we quantified the energy dissipation in the damage zone of a double-network (DN) hydrogel using a mechanochemical technique based on mechanoradical polymerization combined with confocal fluorescence microscopy. We found that, in addition to energy dissipation in a relatively narrow yield region, the dissipation in the wide preyielding region and the intrinsic fracture energy also has a large contribution to the fracture energy. Moreover, the fracture energy of a prestretched sample, in which the dissipative capacity is nearly depleted, suggests that the intrinsic fracture energy is higher than the fracture energy of the second network. These findings modify the previous understanding that the fracture energy of DN gels is dominated by the energy of the yielding zone formation