13C ENDOR揭示了D1多C末端在光系II氧化物进化复合体中直接与Mn结合
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
概括
这项研究使用了Mims ENDOR光谱学来研究光系统II中的团. 这些发现支持D1-Ala344碳酸盐与团的直接结合,这对于理解氧气演变至关重要.
科学领域:
- 生物物理化学 生物物理化学
- 光合作用研究研究 光合作用研究
- 生物有机化学 生物有机化学
背景情况:
- 抗铁磁合的Mn (III) Mn (IV) 二次体是复杂的生物交换相互作用的重要模型.
- 光系II (PSII) 中的氧进化复合体 (OEC) 含有这种二次体,是光合作用的关键.
- 了解OEC内部的直接相互作用,特别是Mn-carboxylate结合,对于阐明其机制至关重要.
研究的目的:
- 要确定D1-Ala344的C端碳酸盐是否直接结合到PSII中的集群.
- 使用Mims ENDOR光谱检测蛋白质衍生的碳酸盐超细相互作用.
- 将实验发现与OEC的结构模型相关联.
主要方法:
- 进行了Q频段 (34 GHz) Mims ENDOR光谱检测,对一个标有碳-13 ((13) C) 的模型Mn(III) Mn(IV) 模数进行检测.
- 类似的ENDOR研究也对来自Synechocystis sp.的PSII进行了研究. PCC 6803,具有选择性和统一的 (13) C 标签.
- 使用实验数据和X射线晶体结构计算和模拟了超细相互作用值 (A(dip) 和A(iso)).
主要成果:
- 模型的Mn{III},Mn{IV}二极管产生了1MHz的同位素高精度合常量 (A{iso}).
- 在使用 (13) C 标签的 PSII 上进行的 ENDOR 研究结果显示,A ((iso) 值为 1.2,1,和 2 MHz.
- 实验中的A(iso) 值表明,Mn-协调碳酸盐部分不太可能表现出明显大于1.2MHz的值.
结论:
- D1多的C端碳酸盐直接与PSII中的集群结合.
- 这一发现支持结构模型 (Loll和Guskov) 提出D1-Ala344与Mn集群的更密切安排.
- 直接氧酸盐结合是理解氧化复合物的催化机制的关键特征.
相关概念视频
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
Although structurally similar to photosystem II (PSII), photosystem I (PSI) is has a different electron supplier and electron acceptor.
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...
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
During the electron transport chain, electrons from NADH and FADH2 are first transferred to complexes I and II, respectively. These two complexes then transfer the electrons to ubiquinol, which carries them further to complex III. Complex III passes the electrons across the intermembrane space to Cyt c, which carries them further to complex IV. Complex IV donates electrons to oxygen and reduces it to water. As electrons pass through complexes I, III, and IV, the energy released aids the pumping...
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...

