Single-macromolecule fluorescence resonance energy transfer and free-energy profiles
Single-macromolecule fluorescence resonance energy transfer and free-energy profiles
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DOI：
10.1021/jp027481o
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发表时间：
2003-05-29
影响因子：
3.3
通讯作者：
Szabo, A
中科院分区：
文献类型：
--
作者：
Gopich, IV;Szabo, A
在单分子荧光共振能量转移（FRET）实验中，在固定的时间窗口T内发射的供体和受体光子被计数，其中包含的动力学和结构信息是什么？为了回答这个问题，一个理论的发展，以获得从持续时间T的轨迹获得的能量转移效率的概率分布。效率是连接到大分子的荧光供体和受体之间的距离的显式函数;因此，效率可以形式上转换为距离。然而，所得到的距离概率分布，或者等效地，平均力或自由能分布的势，取决于观测时间窗T的大小。说明性的计算提出的无规卷曲聚合物和蛋白质，表现出两种状态的折叠动力学。它被发现，表观自由能的配置文件看起来物理上合理的，即使是很长的观察时间，在此期间发生显着的波动。然而，这样的配置文件是欺骗性的，除非观察时间是大约一个数量级小于施主-受主距离的弛豫时间。
What is the dynamical and structural information contained in single-molecule fluorescence resonance energy, transfer (FRET) experiments where the donor and acceptor photons emitted during a fixed time window T are counted? To answer this question, a theory is developed to obtain the probability distribution of the energy-transfer efficiency obtained from trajectories of duration T. The efficiency is an explicit function of the distance between a fluorescent donor and acceptor attached to the macromolecule; thus, the efficiency can formally be converted to a distance. The resulting distance probability distribution or, equivalently, the potential of mean force or free-energy profile, however, depends on the size of the observation time window T. Illustrative calculations are presented for a random coil polymer and for a protein that exhibits two-state folding kinetics. It is found that the apparent free-energy profiles look physically reasonable, even for long observation times during which significant fluctuations occur. Such, profiles are, however, deceptive unless the observation time is approximately an order of magnitude smaller than the relaxation time of the donor-acceptor distance.