Crystal structures of materials tell us what kinds of reactions have occurred in the same way as microstructures of metal show the reactions. Various kinds of chemical and physical reactions as well as metallurgical ones are involved in the iron and steel making process,where crystallography plays important roles for revealing their reaction mechanisms. Two examples are shown: corrosion and sintering. In situ observation of reactions at the liquid/metal interface successfully showed the mechanism of atmospheric corrosion, resulting in development of the new-type weathering steel. In situ observation of reactions in the CaO-Fe2O3 system at high temperatures revealed its reaction mechanism, providing crucial and fundamental information on the sintering accompanying solidification, precipitation, and formation of calcium ferrites from the molten oxide.
We prepared oxyhydrides of the perovskite ATiO3 （A＝Ba, Sr, Ca） via low-temperature reduction using CaH2. The obtained oxyhydrides are stable against temperature as well as A-site substitution, and the hydride species are exchangeable with outer hydrogen gas, implying the hydride diffusion through the lattice. The exchange temperature depends on the A-site cation,and ranged from 380-460 ℃. Epitaxial thin films of these oxyhydrides were also fabricated. The films show a metallic conductivity.
MATE （multidrug and toxic compound extrusion） family transporters are conserved in the three primary kingdoms, and export xenobiotics using an electrochemical gradient of H+ or Na+ across the membrane.1) MATE transporters confer multidrug resistance （MDR） to bacterial pathogens2) and cancer cells.3) Therefore, the development of MATE inhibitors has long been awaited in the field of clinical medicine.4) Here we present the crystal structures of the H+-driven MATE transporter from Pyrococcus furiosus in two distinct apo-form conformations, and in complexes with a derivative of the antibacterial drug norfloxacin and three in vitro selected thioether-macrocyclic peptides. The structures, combined with functional analyses, revealed that the protonation of Asp41 on the N-terminal lobe induces the bending of TM1, which in turn collapses the N-lobe cavity, thereby extruding the substrate drug to the extra-cellular space. Moreover, two of the macrocyclic peptides bind the central cleft in distinct manners, which correlate with their inhibitory activities.
The cyanide-insensitive alternative oxidase （AOX） is a diiron carboxylate protein that catalyzes the four-electron reduction of dioxygen to water by ubiquinol. In Trypanosoma brucei, a parasite that causes human African sleeping sickness, AOX plays a critical role in the survival of the parasite in its bloodstream form. Since AOX is absent from mammals, this protein represents a novel and promising therapeutic target. We determined the first crystal structures of the trypanosomal alternative oxidase in the absence and presence of ascofuranone and its derivatives, which are drug candidates for African trypanosomiasis. All structures reveal that AOX is a homodimer with a non-haem diiron carboxylate active-site buried within a four-helix bundle.