Antifreeze proteins (AFPs) are characterized by their ability to adsorb to the surface of ice crystals and prevent any further crystal growth. AFPs have independently evolved for this purpose in a ...variety of organisms that encounter the threat of freezing, including many species of polar fish, insects, plants and microorganisms. Despite their diverse origins and structures, it has been suggested that all AFPs can organize ice-like water patterns on one side of the protein (the ice-binding site) that helps bind the AFP to ice. Here, to test this hypothesis, we have solved the crystal structure at 2.05 Å resolution of an AFP from the longhorn beetle, Rhagium mordax with five molecules in the unit cell. This AFP is hyperactive, and its crystal structure resembles that of the R. inquisitor ortholog in having a β-solenoid fold with a wide, flat ice-binding surface formed by four parallel rows of mainly Thr residues. The key difference between these structures is that the R. inquisitor AFP crystallized with its ice-binding site (IBS) making protein-protein contacts that limited the surface water patterns. Whereas the R. mordax AFP crystallized with the IBSs exposed to solvent enabling two layers of unrestricted ordered surface waters to be seen. These crystal waters make close matches to ice lattice waters on the basal and primary prism planes.
The mechanism of the clustering in Al-Mg-Si-Cu alloys has been a long-standing controversial issue. Here, for the first time, the mechanism of the clustering in the alloy was investigated by a ...Kinetic Monte Carlo (KMC) approach. In addition, reversion aging (RA) was carried out to evaluate the simulation results. The results showed that many small-size clusters formed rapidly in the early stages of aging. With the prolongation of aging time, the clusters merged and grew. The small clusters formed at the beginning of aging in Al-Mg-Si-Cu alloy were caused by initial vacancies (quenching vacancies). The merging and decomposition of the clusters were mainly caused by the capturing of vacancies, and the clusters had a probability to decompose before reaching a stable size. After repeated merging and decomposition, the clusters reach stability. During RA, the complex interaction between the cluster merging and decomposition leaded to the partial irregular change of the hardness reduction and activation energy.
Calpains are intracellular, calcium-activated cysteine proteases. Calpain-3 is abundant in skeletal muscle, where its mutation-induced loss of function causes limb-girdle muscular dystrophy type 2A. ...Unlike the small subunit–containing calpain-1 and -2, the calpain-3 isoform homodimerizes through pairing of its C-terminal penta-EF-hand domain. It also has two unique insertion sequences (ISs) not found in the other calpains: IS1 within calpain-3’s protease core and IS2 just prior to the penta-EF-hand domain. Production of either native or recombinant full-length calpain-3 to characterize the function of these ISs is challenging. Therefore, here we used recombinant rat calpain-2 as a stable surrogate and inserted IS1 into its equivalent position in the protease core. As it does in calpain-3, IS1 occupied the catalytic cleft and restricted the enzyme’s access to substrate and inhibitors. Following activation by Ca2+, IS1 was rapidly cleaved by intramolecular autolysis, permitting the enzyme to freely accept substrate and inhibitors. The surrogate remained functional until extensive intermolecular autoproteolysis inactivated the enzyme, as is typical of calpain-2. Although the small-molecule inhibitors E-64 and leupeptin limited intermolecular autolysis of the surrogate, they did not block the initial intramolecular cleavage of IS1, establishing its role as a propeptide. Surprisingly, the large-molecule calpain inhibitor, calpastatin, completely blocked enzyme activity, even with IS1 intact. We suggest that calpastatin is large enough to oust IS1 from the catalytic cleft and take its place. We propose an explanation for why calpastatin can inhibit calpain-2 bearing the IS1 insertion but cannot inhibit WT calpain-3.
Display omitted
•Elongated beta-sandwich repeats are a major part of bacterial RTX adhesins.•The repeats are arranged in tandem to extend away from the bacterial surface.•Calcium ions are coordinated ...in the linkers between repeats to stiffen the protein.•Rigidification of the tandem repeats further helps extension of the adhesin.•The repeats differ greatly between species, but all have Ca2+ in their linkers.
RTX adhesins are long, multi-domain proteins present on the outer membrane of many Gram-negative bacteria. From this vantage point, adhesins use their distal ligand-binding domains for surface attachment leading to biofilm formation. To expand the reach of the ligand-binding domains, RTX adhesins maintain a central extender region of multiple tandem repeats, which makes up most of the proteins’ large molecular weight. Alignments of the 10-15-kDa extender domains show low sequence identity between adhesins. Here we have produced and structurally characterized protein constructs of four tandem repeats (tetra-tandemers) from two different RTX adhesins. In comparing the tetra-tandemers to each other and already solved structures from Marinomonas primoryensis and Salmonella enterica, the extender domains fold as diverse beta-sandwich structures with widely differing calcium contents. However, all the tetra-tandemers have at least one calcium ion coordinated in the linker region between beta-sandwich domains whose role appears to be the rigidification of the extender region to help the adhesin extend its reach.
Segregation engineering (SE) can optimize the microstructure and improve the properties of traditional alloys. AlCoCrFeNi2.1 alloy has been declared as a promising superalloy. Mo can improve high ...temperature performance, AlCoCrFeMo0.05Ni2 alloy has been developed. To evaluate the SE in AlCoCrFeMo0.05Ni2 HEA, annealing process of the alloy was investigated. The experimental results showed that a large number of metastable phases were formed at the lattice defects in the as-cast alloy during annealing. And the main phase of the alloy annealed at 800 °C for 72 h changed from FCC to BCC structures. Moreover, a large number of dislocations and stacking faults were formed in the (Ni, Al)-rich BCC new phase, and finally turned into nanocrystals or twins. At the same time, the (Cr, Mo)-rich BCC phase changed from spherical to rod, square and dish-like during the annealing. The growth of the (Cr, Mo)-rich BCC phase and the mutual restriction of different phases resulted in the refinement of the (Ni, Al)-rich BCC phase during annealing. The high temperature ductility of the alloy has been improved significantly. At 700 °C, its elongation reached 80%, while the strength had still up to 500 MPa.
Display omitted
•A large number of dislocations and stacking faults were discovered in a new metastable (Ni, Al)-rich BCC phase.•Annealing twin transformed from the metastable phase has been found in an as-cast AlCoCrFeMo0.05Ni2 high entropy alloy.•The growth of (Cr, Mo)-rich BCC phase during annealing process resulted in the refinement of (Ni, Al)-rich BCC phase.
The effect of aging on the microstructure and property of a newly high entropy alloy (HEA) with balanced strength-ductility and good high temperature property is studied. The results show that the ...microstructure of AlCoCrFeMo0.05Ni2 high entropy alloy forging consists of Fe, Co rich FCC phase, Al, Ni rich BCC phase and Cr, Mo rich BCC phase. The area ratios of FCC and BCC phases are about 61% and 39%, respectively. After aged at 680 °C and 700 °C, an Al, Ni rich needle-like phase with FCC structure is precipitated in the original FCC phase; the Cr, Mo rich BCC phase grows up, aggregates at the grain boundary and forms finally block σ phase. The microstructure of the alloy aged at 700 °C is refined continuously without change in the area ratios of the Al, Ni BCC phase as the aging time prolonged. The mechanical property of the alloy aged at 680 °C for 8 h is excellent at room temperature. And the yield strength, tensile strength, and elongation are 1080 MPa, 1393 MPa, 19.5%, respectively. The elongation of the alloy aged at 700 °C for 150 h can reach up to 80% at 700 °C.
Display omitted
•AlCoCrFeMo0.05Ni2 HEA designed by our group has excellent balanced strength-ductility.•Electroslag ingot of AlCoCrFeMo0.05Ni2 HEA has been forged into φ 16 mm bar successfully.•The needle-like phase is the mainly aging strengthening phase in AlCoCrFeMo0.05Ni2 HEA.•The σ phase at the grain boundary of the aged alloy is evolved from the spherical Cr, Mo rich phase.•The high temperature ductility of the alloy increased significantly due to the ultrafined microstructure.
The efficient TiO2 NTs/Sn3O4 photocatalysts were synthesized by the hydrothermal deposition of Sn3O4 on TiO2 nanotube arrays (TiO2 NTs), and the morphology, microstructure and photocatalytic property ...were adjusted by changing the alkali kind. The TiO2 NTs/Sn3O4 prepared with NaOH exhibited the outstanding photoelectric conversion and photocatalytic environment remediation/H2 evolution. The methylene blue (MB) dye and Cr(VI) could be removed by the as-prepared photocatalysts under visible light irradiation, and •O2−/•OH radicals were the main active species for MB photodegradation. Furthermore, the high photocatalytic H2 evolution rate was as high as 6.49 μmol cm−2 h−1. The outstanding photocatalytic activity and stability of TiO2 NTs/Sn3O4 photocatalysts would exhibit attractive prospect in the wastewater remediation and electric energy/hydrogen generation.
•EHEA are successfully prepared by EHLC.•EHLC coating have a finer microstructure, higher and more uniform hardness.•The EHLC coating consists of FCC/L12 and B2/BCC structures.•The EHLC coating ...elemental distribution is more uniform than the LC coating.
Anisotropy in a thicker coating due to different cross-sectional microstructures is usually a major concern when used for an engineering application. Here, we report that extreme high-speed laser cladding (EHLC) can fabricate coating with thickness of dozens and hundreds microns, whose microstructure and hardness are uniform. Due to lower heat input and rapid cooling, the microstructures with same growth direction under the EHLC are confirmed to connect each other. Based on our present investigation, the EHLC technique opens new avenues for fabricating coatings especially for high-entropy alloy coatings in which uniform microstructure and hardness are required.
Display omitted
•The Bi2WO6/Bi2MoO6 heterojunctions were synthesized on TiO2 NTs.•TiO2 NTs/ Bi2WO6-Bi2MoO6 photoelectrodes displayed the attractive photocatalytic performance.•The direct Z-scheme ...photocatalytic mechanism was explored.
In this paper, the direct Z-scheme Bi2WO6-Bi2MoO6 heterojunctions were constructed by the simple hydrothermal deposition on TiO2 nanotube arrays (TiO2 NTs). The results revealed Bi2WO6/Bi2MoO6 heterojunctions dramatically enhanced the solar absorption and slowed the electron recombination, which improved the photoelectrocatalytic pollutant removal property, and •OH and •O2 radicals were the decisive active species. Moreover, the TiO2 NTs/Bi2WO6-Bi2MoO6 photoelectrode exhibited excellent photoelectric conversion and photoelectrocatalytic H2 evolution properties, much higher than the data of TiO2 NTs/Bi2WO6 and TiO2 NTs/Bi2MoO6 photoelectrodes. The visible light photoelectrocatalytic H2 evolution rate of TiO2 NTs/Bi2WO6-Bi2MoO6 photoelectrode was 38.03 μmol·h−1·cm−2, and it still showed high photocatalytic activity after several experimental cycles. The outstanding photocatalytic activity of TiO2 NTs/Bi2WO6-Bi2MoO6 sample provides a referential template of the Z-scheme heterojunction construction for the application in photocatalytic pollutant removal and H2 evolution.
PDF
