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13C ENDORは,D1ポリペプチドのC端が,光系IIの酸素進化複合体におけるMnと直接結合していることを示しています
Jamie A Stull1, Troy A Stich, Rachel J Service
1Department of Chemistry, University of California-Davis, Davis, California 95616, USA.
Journal of the American Chemical Society
|December 30, 2009
まとめ
この研究では,Mims ENDOR光譜を用いて,光システムIIのマンガン群を調査しました. この発見は,D1-Ala344カルボキシラートがマンガン群に直接結合することを支持しており,これは酸素の進化を理解する上で極めて重要です.
科学分野:
- 生物物理化学 生物物理化学
- 光合成研究 研究 光合成研究
- バイオ・オーガニック化学 バイオ・オーガニック化学
背景:
- 抗鉄磁性結合のMn (III) Mn (IV) ダイマーは,複雑な生物交換相互作用の重要なモデルである.
- 光学系II (PSII) の酸素進化複合体 (OEC) は,このような二次体を含み,光合成の鍵となっている.
- OEC内の直接的な相互作用,特にMn-carboxylate結合を理解することは,そのメカニズムの解明に不可欠です.
研究 の 目的:
- D1-Ala344のC端カルボキシラートがPSIIのマンガネスクラスターに直接結合しているかどうかを判断する.
- Mims ENDORスペクトロスコーピーを用いて,タンパク質由来カルボキシラートハイパーファインの相互作用を検知する.
- 実験結果とOECの構造モデルを相関させる.
主な方法:
- Q帯 (34GHz) Mims ENDORスペクトロスコピーは,炭素13 ((13) C) とラベルを貼ったモデル Mn(III) Mn(IV) ダイマーで実施されました.
- Synechocystis sp. の PSII にも同様の ENDOR 研究が実施されました. PCC 6803は,選択的で均一な (13) Cラベルを付けています.
- 超微細相互作用値 (A(dip) とA(iso)) は,実験データとX線結晶学構造を用いて計算およびシミュレートされた.
主要な成果:
- モデルMn(III) Mn(IV) ダイマーは,1MHzのイソトロピック高精度カップリング定数 (A(iso)) を得ました.
- (13) CラベリングによるPSIIに関するENDORの研究は,A(iso) 値が1.2,1,および2MHzであることを示した.
- 実験のA(iso) 値は,Mn-コーディネートカルボキシラート分子が1.2MHzより大幅に大きい値を示す可能性が低いことを示唆しています.
結論:
- D1ポリペプチドのC末端のカルボキシラートは,PSII.のマンガン群に直接結合している.
- この発見は,D1-Ala344がMn群集により近い配置を提案する構造モデル (LollとGuskov) を支持しています.
- 直接カルボキシラート結合は,酸素進化複合体の触媒機構を理解するための重要な特徴である.
関連する概念動画
Photosystem II
The multi-protein complex photosystem II (PS II) harvests photons and transfers their energy through its bound pigments to its reaction center, and ultimately to photosystem I (PSI) through the electron transport chain. The pigments responsible for caputirng the light energy in photosystems include chlorophyll a, chlorophyll b, and carotenoids.
The pigment molecules are arranged across two photosystem domains — the antenna complex and the reaction center. The main aim of the pigment molecules...
The pigment molecules are arranged across two photosystem domains — the antenna complex and the reaction center. The main aim of the pigment molecules...
Photosystem I
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Both these photosystems work in concert. An excited electron from PSII is relayed to PSI via an electron transport chain in the thylakoid membrane of the chloroplast, which is comprised of the carrier molecule plastoquinone, the dual-protein cytochrome complex, and plastocyanin. As electrons move between PSII and PSI, they lose energy and must be re-energized...
Electron Transport Chain: Complex III and IV
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The Photochemical Reaction Center
Reaction centers are pigment-protein complexes that initiate energy conversion from photons to chemical entities. Therefore, photochemical reaction center is a more appropriate term that describes these complexes. The Nobel laureates Robert Emerson and William Arnold provided the first experimental evidence of photochemical reaction centers by demonstrating the participation of nearly 2,500 chlorophyll molecules for the release of just one molecule of oxygen. Despite thousands of photosynthetic...
Photosystems
Photosystems are multiprotein complexes that form the functional units of photosynthesis in plants, algae, and cyanobacteria. They are found embedded in the membrane of tiny sac-like structures called thylakoids placed inside the chloroplast.
Functioning of Photosystems
Photosystems contain many pigment molecules, such as chlorophylls and carotenoids, arranged in a particular organization across two domains — the antenna complex and the reaction center. The main aim of the pigment molecules...
Functioning of Photosystems
Photosystems contain many pigment molecules, such as chlorophylls and carotenoids, arranged in a particular organization across two domains — the antenna complex and the reaction center. The main aim of the pigment molecules...
The Antenna Complex
Plants and other photosynthetic organisms comprise pigments capable of absorption of direct sunlight. These pigments are present in the reaction center - the main site of photochemical reactions as well as in the antenna complex. Under average light conditions, the rate at which reaction center pigments absorb light is far below the electron transport chain's capacity. As a result, the reaction center alone cannot provide enough energy to drive photosynthesis. The photosynthetic efficiency can...
