<教育デザインフォーラム学生発表会>発表会に関する小委員会報告

departmental bulletin pape

高速イオンの古典的軌道損失を用いた非接触電場制御

(1)本研究で開発した高速イオンの軌道計算コ-ドならびに径方向電場分布計算コ-ドを改良し、高速中性粒子入射による電場制御を中・大型トカマク装置に適用した場合に期待される電場分布の制御性を明かにした。得られた結果は、 [1]高速中性粒子入射(NBI)により生成される2種類径方向のイオン束(軌道損失と荷電交換損失、トロイダル方向の運動量の輸送に伴う径方向の損失の 2種類)を数値計算で求め、NBIをプラズマ周辺部に局在化して入射し、NBIの加速エネルギ-等に最適化を図ることにより、プラズマ周辺部に大きな径方向外向きのイオン束が形成されることを示した。 [2]NBIによる径方向外向きあるいは内向きの損失イオン束は、各磁気面上における両極性条件を満足するように変化する。トカマク装置で得られているH モ-ドプラズマに見られるような周辺部の電場を変化させるようにNBI入射方法を最適化した場合、中型トカマク装置では、100kW程度のNBI入力で 50V/cm程度の径方向電場の変化を誘起できる可能性がある。 [3]今後の問題点として、電場計算に用いている電子・イオンの拡散係数にはリップル損失を取り入れた新古典拡散係数を用いており、より現実的な異常拡散モデルを用いた電場分布計算を行う必要がある。また、本研究において示されたNBIによる電場制御特性を実際のトカマク装置で検証し、電場制御による閉じ込め特性改善の可能性を明かにする必要がある。 (2)小型トカマク装置における交流リミタバイアス実験により、100kHzまでの周波数領域でリミタ前面からSOL領域にわたり〜30V/cmの振動径電場を形成できることを示した。この振動径電場により誘起されるイオンの分極ドリフトと粒子衝突過程を利用して不純物の磁場を横切る拡散を助長することによる不純物排出の可能性を検討した。科学研究費補助金 研究種目:一般研究(B) 課題番号:03452285 研究代表者:上杉 喜彦 研究期間:1991-1992年度research repor

Observation of the Decay B0→D±D*∓

journal articl

インドにおける日本研究の現状 : 問題と将来性

departmental bulletin pape

Identification of Key Residues That Confer <i>Rhodobacter sphaeroides</i> LPS Activity at Horse TLR4/MD-2

<div><p>The molecular determinants underpinning how hexaacylated lipid A and tetraacylated precursor lipid IVa activate Toll-like receptor 4 (TLR4) are well understood, but how activation is induced by other lipid A species is less clear. Species specificity studies have clarified how TLR4/MD-2 recognises different lipid A structures, for example tetraacylated lipid IVa requires direct electrostatic interactions for agonism. In this study, we examine how pentaacylated lipopolysaccharide from <i>Rhodobacter sphaeroides</i> (RSLPS) antagonises human TLR4/MD-2 and activates the horse receptor complex using a computational approach and cross-species mutagenesis. At a functional level, we show that RSLPS is a partial agonist at horse TLR4/MD-2 with greater efficacy than lipid IVa. These data suggest the importance of the additional acyl chain in RSLPS signalling. Based on docking analysis, we propose a model for positioning of the RSLPS lipid A moiety (RSLA) within the MD-2 cavity at the TLR4 dimer interface, which allows activity at the horse receptor complex. As for lipid IVa, RSLPS agonism requires species-specific contacts with MD-2 and TLR4, but the R2 chain of RSLA protrudes from the MD-2 pocket to contact the TLR4 dimer in the vicinity of proline 442. Our model explains why RSLPS is only partially dependent on horse TLR4 residue R385, unlike lipid IVa. Mutagenesis of proline 442 into a serine residue, as found in human TLR4, uncovers the importance of this site in RSLPS signalling; horse TLR4 R385G/P442S double mutation completely abolishes RSLPS activity without its counterpart, human TLR4 G384R/S441P, being able to restore it. Our data highlight the importance of subtle changes in ligand positioning, and suggest that TLR4 and MD-2 residues that may not participate directly in ligand binding can determine the signalling outcome of a given ligand. This indicates a cooperative binding mechanism within the receptor complex, which is becoming increasingly important in TLR signalling.</p></div

RSLPS is a partial agonist at horse TLR4/MD-2 and competitive antagonist at human TLR4/MD-2.

<p>HEK293 cells were transiently transfected with horse or human TLR4, MD-2 and CD14, together with reporter constructs NF-κB-luc and phRG-TK. Cells were stimulated 48 hours later for 6 hours. Data are from a representative experiment (n = 3 experiments) and expressed as triplicate mean ±SEM for that experiment, relative to the maximum ECLPS response. A and B) Horse TLR4/MD-2/CD14-transfected cells were stimulated with increasing concentrations of RSLPS or increasing concentrations of ECLPS (A), or increasing concentrations of RSLPS+10 ng/ml ECLPS (B). C) Human TLR4/MD-2/CD14-transfected cells were stimulated with increasing concentrations of ECLPS in the presence of 0, 1, 10 and 100 ng/ml RSLPS.</p

RSLPS requires specific residues within horse MD-2 and TLR4, yet is independent of CD14.

<p>HEK293 cells were transiently transfected with combinations of human and horse TLR4 and MD-2, with or without horse CD14, and reporter constructs NF-κB-luc and phRG-TK. Cells were stimulated 48 hours later for 6 hours with 100 ng/ml RSLPS, 10 ng/ml ECLPS, 100 ng/ml RSLPS+10 ng/ml ECLPS, or medium alone. Data are from a representative experiment (n = 3 experiments) and expressed as triplicate mean ±SEM for that experiment, relative to the maximum ECLPS response. A) Cells were transfected with different combinations of human and horse TLR4 and MD-2. B) Horse TLR4/MD-2 was transfected with and without CD14. C) MD-2 mutants were transfected with horse TLR4/CD14. D) TLR4 mutants were transfected with horse MD-2/CD14.</p

High-Resolution Structure of Murine Interleukin 1 Homologue IL-1F5 Reveals Unique Loop Conformations for Receptor Binding Specificity^†^,^‡

Interleukin-1 (IL-1) F5 is a novel member of the IL-1 family. The IL-1 family are involved in innate immune responses to infection and injury. These cytokines bind to specific receptors and cause activation of NFκB and MAP kinase. IL-1F5 has a sequence identity of 44% to IL-1 receptor antagonist (IL-1Ra), a natural antagonist of the IL-1 system. Here we report the crystal structure of IL-1F5 to a resolution of 1.6 Å. It has the same β-trefoil fold as other IL-1 family members, and the hydrophobic core is well conserved. However, there are substantial differences in the loop conformations, structures that confer binding specificity for the cognate receptor to IL-1β and the antagonist IL-1Ra. Docking and superimposition of the IL-1F5 structure suggest that is unlikely to bind to the interleukin1 receptor, consistent with biochemical studies. The structure IL-1F5 lacks features that confer antagonist properties on IL-1Ra, and we predict that like IL-1β it will act as an agonist. These studies give insights into how distinct receptor specificities can evolve within related cytokine families

RSLPS activity requires the presence of both R385 and P442 in horse TLR4.

<p>HEK293 cells were transiently transfected with combinations of human and horse TLR4 and MD-2, together with horse CD14 and reporter constructs NF-κB-luc and phRG-TK. Cells were stimulated 48 hours later for 6 hours. Data are from a representative experiment (n = 3 experiments) and expressed as triplicate mean ±SEM for that experiment, relative to the maximum ECLPS response. A) TLR4 point mutants were transfected with horse MD-2/CD14 and stimulated with 100 ng/ml RSLPS, 10 ng/ml ECLPS, 100 ng/ml RSLPS+10 ng/ml ECLPS or medium alone. B) TLR4 point mutants were transfected with horse MD-2/CD14 and stimulated with 1 µg/ml lipid IVa, 1 µg/ml lipid IVa+10 ng/ml ECLPS, or medium alone.</p

RSLA and lipid IVa sit differently within the MD-2 pocket.

<p>A) Docking models of RSLA and lipid IVa bound to horse TLR4/MD-2 were overlaid to assess ligand and receptor positioning. The acyl chains of RSLA (blue) sit more deeply in the MD-2 (pink) pocket than lipid IVa (green), and the R2 chain of RSLA protrudes from the MD-2 pocket to contact TLR4* (grey). The 1-PO₄ is also moved away from TLR4 due to lowering of the diglucosamine backbone. B) Overlay of RSLA (blue; horse model), lipid IVa (green; horse model) and lipid A (red; human crystal) in situ in the MD-2 pocket. TLR4 and MD-2 have been removed for clarity. The PO₄ groups and acyl chains of all three ligands sit somewhat differently to one another within the pocket. Lipid A and RSLA appear to occupy a similar volume within the pocket.</p