Membrane-associated proteins play pivotal roles in a wide variety of cellular events, such as bioenergetics, membrane transport and signal transduction. In eukaryotic cells, membrane traffic in the endomembrane system is also regulated by membrane-associated proteins. Here we report the structural analyses of membrane-associated proteins as follows ; the bacterial photosynthetic reaction center converting the light energy into chemical energy, the γ1-adaptin ear domain of the AP-1 complex in the membrane traffic and the signaling molecule reelin regulating the layer formation in the brain. We discuss their structural features from the viewpoint of protein-protein interactions.
Whereas α-helix has an almost unique secondary structure, β-structure or conformation appears in various structural motifs. Basically, β-structure is either in parallel or anti-parallel β-sheet, but recent structure determination of phage and viral structural proteins revealed a variety of new structure motifs such as β-helix, β-spiral, and β-propeller in addition to traditional parallel and anti-parallel β-sheet, β-barrel or β-sandwich. This article will review these new β-structure motifs and their functional implications.
Transparent insulating oxide 12CaO·7Al2O3 (C12A7) is converted into electronic conductor by replacing the oxygen ions in the crystallographic cages with electrons. At the low electron concentration (Ne) <-1020 cm-3, C12A7 exhibits semiconductive properties due to hopping of localized electron. With increase of Ne, it becomes metallic state at a critical Ne-1×1021 cm-3. Fully oxygen-replaced C12A7 (C12A7: e-) may be regarded as a room-temperature-stable electride in which electrons serve as anions. Small work function of 2.4 eV comparable to that in metal potassium is a characteristic of C 12A7: e- and makes it a promising candidate for electron emitting source.
The high-pressure formation of the bulk metallic glass of elemental Zr and Ti, which has been recently reported, is verified by a newly developed angle dispersive X-ray diffraction (ADX) system using a large volume multi-anvil apparatus equipped with X-ray transparent anvils. The ADX data revealed that Zr and Ti remain as a crystalline form at high-pressure and temperature condition where the amorphization has been reported. The misinterpretation in the previous papers is attributed to the anomalous rapid grain growth that is related to the characteristic lattice dynamic and the resulting anomalously fast self diffusion in the high-temperature phases of Zr and Ti.
Firefly emits visible yellow-green light. The bioluminescence reaction is carried out by the enzyme luciferase. The bioluminescence color change by a single amino acid substitution in luciferase is most attractive interest, however the molecular mechanism has been unclear. In fact S286N mutant of Genji-botaru luciferase emits red light. We have determined wild-type and S286N crystal structures of Genji-botaru luciferase and uncovered a structural explanation for the color control mechanism in firefly luciferase. The degree of molecular rigidity of the excited oxyluciferin is involved in the color of bioluminescence during emission reaction.
ADAMs (A disintegrin and Metalloproteinases) are major sheddases possessing extracellular metalloproteinase/disintegrin/cysteine-rich (MDC) domains. ADAMs uniquely display both proteolytic and adhesive functions on the cell surface, however, most of their physiological targets and adhesion mechanisms remain unclear. Crystal structures of vascular apotosis-inducing protein- 1 (VAP 1), a snake venom homolog of mammalian ADAMs, reveal ADAMs' MDC domain architecture and a potential target recognition site. The C-shaped structure implies interplay between the ADAMs' proteolytic and adhesive domains and suggests a molecular mechanism for ADAMs' target recognition for shedding.
Degradation of cell membrane and mucosa, of which phospholipads are major components, and production of lipid mediators are roles of phospholipases from pathogenic bacteria to grow, survive and spread in the host organism. The studies on the enzymes are important for the pathobiology of bacterial infectious disease. The crystal structure of Sphingomyelinase from Bacillus cereus revealed the structure basis of the phospholipase C and hemolysis activities in a divalent cation dependent manner. The water-bridged double divalent cations were concluded to be the catalytic architecture to the phospholipase C activity. In addition, the β-hairpin structure with aromatic amino acid residues was shown to be involved in the membrane binding of the enzyme as a part of the hemolysis activity.