Volume 09, No.1
January issue 2004
1. SPring-8の現状／PRESENT STATUS OF SPring-8
3. 最近の研究から／FROM LATEST RESEARCH
Crystal Structures of Bacterial Lipoprotein Localization Factors, LolA and LolB
理化学研究所 播磨研究所 Harima Institute, RIKEN、京都大学 大学院理学研究科 Graduate School of Science, Kyoto University
- Five Lol proteins are involved in the lipoprotein transport in Gram-negative bacteria. Crystal structures of a lipoprotein-specific periplasmic chaperone, LolA, and an outer membrane lipoprotein receptor, LolB from Escherichia coli were determined using diffraction data collected at the beamlines of SPring-8. Despite their dissimilar amino acid sequences (identity ~ 8%), the structures of LolA and LolB are strikingly similar to each other. Both have a hydrophobic cavity consisting of an unclosed β-barrel and an α-helical lid. The cavity represents a possible binding site for the lipid moiety of lipoproteins. However, the structural differences in size and shape of hydrophobic inner spaces between LolA and LolB are highly connected to the functional differences between two proteins. Furthermore, these structural differences between two proteins provide significant insights into the molecular mechanisms underlying the energy-independent transfer of lipoproteins from LolA to LolB, and from LolB to the outer membrane.
− 超伝導から量子コンピュータまで −
Possibility of New Nano Devices Using Nano Clusters Colored by Silicon Isotopes
−From Superconductors to Quantum Computers −
大阪市立大学大学院 理学研究科 Graduate School of Science, Osaka City University、慶應義塾大学 理工学部 Faculty of Science and Technology, Keio University、名古屋大学大学院 工学研究科 Graduate School of Engineering, Nagoya University、広島大学大学院 工学研究科 Graduate School of Engineering, Hiroshima University
- VIth group elements like C, Si, Ge and Sn make clusters consisting of pentagonal and/or hexagonal plolyhedra. A avarious crystals having hierachical structure can be constructed on a basis of these clusters. Recent strong demand from the field of isotope engineering for semiconductors has spurred on efforts that have led to the successful separation of stable Si isotopes. The combination of nano clusters and pure isotopes may open a new field of materials science. The present paper describnes, as such examples, the clarification of superconducting mechanism of the first discovered silicon-network Si46 superconductor. An approach of all silicon quantum computors using 28Si isotope is also demonstrated.
− 単結晶窒化ガリウム育成の新手法 −
Congruent Melting of Gallium Nitride at High Pressure and Its Application to Single Crystal Growth
日本原子力研究所 関西研究所 放射光科学研究センター Synchrotron Radiation Research Center, Kansai Research Establishment, JAERI、スプリングエイトサービス㈱ SPring-8 Service Co., Ltd
- The decomposition and melting behaviors of GaN under high pressures and temperatures were studied by in situ x-ray diffraction experiments using a large volume multi-anvil high-pressure apparatus at beamline BL14B1. GaN decomposed into Ga melt and N2 at lower pressures than 5.5 GPa. At pressures above 6.0 GPa, however, congruent melting of GaN occurred around 2220 ℃, and decreasing the temperature allowed the GaN melt to crystallize to the original structure. Single crystals of GaN were formed by cooling the melt slowly under high pressures and were recovered at ambient conditions. The present results have great potential in providing high quality bulk single crystals of GaN, which are desirable substrates for fabricating optoelectronic devices.