Single-molecule spectroscopy reveals photosynthetic LH2 complexes switch between emissive states
Single-molecule spectroscopy reveals photosynthetic LH2 complexes switch between emissive states
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DOI：
10.1073/pnas.1310222110
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发表时间：
2013-07-02
影响因子：
11.1
通讯作者：
Moerner, W. E.
中科院分区：
文献类型：
--
作者：
Schlau-Cohen, Gabriela S.;Wang, Quan;Moerner, W. E.
光合生物在低光强度下通过以接近单位量子效率将光能转化为化学能而蓬勃发展，在高光强度下通过安全地消散多余的光能和有害光产物而蓬勃发展。平衡这两种功能的分子机制仍未完全描述。表征这些过程的机制的一个关键障碍是，它们发生在蛋白质内，随着时间的推移，各个蛋白质之间甚至单个蛋白质内的激发态特性都会发生巨大变化。在系综测量中，这些激发态特性仅显示为平均值。为了克服这种平均现象，我们在单蛋白水平上研究了来自嗜酸红假单胞菌的紫色细菌天线蛋白光捕获复合物 2 (LH2)。我们使用室温单分子技术（反布朗动电陷阱）来研究溶液相（非微扰）环境中的 LH2。通过同时测量单个 LH2 复合物的荧光强度、寿命和光谱，我们识别出三种不同的状态，并观察它们在几秒的时间尺度上发生的转变。我们的结果表明，LH2 复合物可能通过构象变化经历光激活转变为猝灭态，并热恢复到基态。这是一种以前未观察到的、可逆的猝灭途径，也是光合生物适应光强度变化的一种机制。
Photosynthetic organisms flourish under low light intensities by converting photoenergy to chemical energy with near unity quantum efficiency and under high light intensities by safely dissipating excess photoenergy and deleterious photoproducts. The molecular mechanisms balancing these two functions remain incompletely described. One critical barrier to characterizing the mechanisms responsible for these processes is that they occur within proteins whose excited-state properties vary drastically among individual proteins and even within a single protein over time. In ensemble measurements, these excited-state properties appear only as the average value. To overcome this averaging, we investigate the purple bacterial antenna protein light harvesting complex 2 (LH2) from Rhodopseudomonas acidophila at the single-protein level. We use a room-temperature, single-molecule technique, the anti-Brownian electrokinetic trap, to study LH2 in a solution-phase (nonperturbative) environment. By performing simultaneous meas-urements of fluorescence intensity, lifetime, and spectra of single LH2 complexes, we identify three distinct states and observe transitions occurring among them on a timescale of seconds. Our results reveal that LH2 complexes undergo photoactivated switching to a quenched state, likely by a conformational change, and thermally revert to the ground state. This is a previously unobserved, reversible quenching pathway, and is one mechanism through which photosynthetic organisms can adapt to changes in light intensities.