Volume 09, No.4
July issue 2004
1. SPring-8の現状／PRESENT STATUS OF SPring-8
3. 最近の研究から／FROM LATEST RESEARCH
Proton Pumping Mechanism of Bovine Heart Cytochrome c Oxidase
– X-ray Crystallographical, Molecular Biological and Infrared Spectroscopical Analyses
兵庫県立大学大学院 生命理学研究科 Graduate School of Life Science, University of Hyogo
- Improved X-ray structures of bovine heart cytochrome c oxidase (at 1.8/1.9 Å resolution in the fully oxidized/reduced states) show that the net positive charge created upon oxidation of the low-spin heme of the enzyme (heme a) drives the active proton transport from the interior of the mitochondria to Asp51 across the enzyme via a water channel and a hydrogen-bond network, located in tandem, and that the enzyme reduction induces proton ejection from the aspartate to the mitochondrial exterior. A peptide bond in the hydrogen-bond network critically inhibits reverse proton transfer through the network. A redox-coupled change in the capacity of the water channel, induced by the hydroxyfarnesylethyl group of heme a, suggests that the channel functions as an effective proton collecting region. The Asp51Asn mutation of the bovine enzyme abolishes its proton-pumping function without impairment of the dioxygen reduction activity. Infrared results indicate that the conformation of Asp51 is controlled only by the oxidation state of heme a. These results indicate that heme a drives the proton pumping process.
Compaction and Structure Formation of Proteins Revealed by Time-Resolved Small Angle X-ray Scattering
大阪大学 蛋白質研究所 Institute for Protein Research, Osaka University、京都大学大学院 工学研究科 Graduate School of Engineering, Kyoto University、（独）理化学研究所 播磨研究所 Harima Institute, RIKEN
- The compaction process in protein folding has not been characterized well due to experimental difficulties. The submillisecond-resolved observation system for small-angle X-ray scattering was developed and applied for the process of apomyoglobin folding. It was demonstrated that the secondary and tertiary structures are largely organized cooperatively; however, the initial folding phase involves a significant collapse of their main chain structures. A common folding mechanism was proposed, in which hydrophobic environments realized by the initial collapse prompts the subsequent formation of helical structures.
Elucidation of the Crystal Structure of the PsbP Protein Involved in the Oxygen Evolution in Photosynthesis
京都大学大学院 生命科学研究科／（独）理化学研究所 播磨研究所 Graduate School of Biostudies, Kyoto University / Harima Institute, RIKEN
- Photosynthesis is a multi-step reaction that utilizes light energy to convert carbon dioxide into sugar and generate oxygen as by-product. The first step of photosynthesis is the oxygen-evolving reaction performed by the protein-pigment complex called “photosystem II”, and PsbP is one of the protein subunits constituting photosystem II. Since PsbP exists only in higher plants and green algae, its existence has been the subject of inquiry in the process of plant evolution. In order to elucidate the origin and function of PsbP from its 3D structure, a high-resolution analysis based on multiple wavelength anomalous dispersion method using the X-ray of SPring-8 was conducted. The result showed that the structure of PsbP was not similar to any known structures in photosystem II from cyanobacteria, primitive organisms doing oxygenic photosynthesis. This research shows one aspect of the evolution of oxygenic photosynthetic organisms.
4. 研究会等報告／WORKSHOP AND COMMITTEE REPORT
5. 談話室・ユーザー便り／OPEN HOUSE･A LETTERS FROM SPring-8 USERS
The 12th SPring-8 Open House -SPring-8 Never Fails to Bring us a Refreshing Surprise!-
“HANDY TIPS AROUND HARIMA SCIENCE GARDEN CITY” will be separately bound from the September 2004 issue (No.5, Vol.9)