Elucidating photoinduced structural changes in phytochromes by the combined application of resonance Raman spectroscopy and theoretical methods
Elucidating photoinduced structural changes in phytochromes by the combined application of resonance Raman spectroscopy and theoretical methods
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DOI：
10.1016/j.molstruc.2011.02.038
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发表时间：
2011-05-03
影响因子：
3.8
通讯作者：
Hildebrandt, P.
中科院分区：
文献类型：
--
作者：
Mroginski, M. A.;von Stetten, D.;Hildebrandt, P.
光敏色素是植物和微生物中一类感红光的光感受器。光活性辅因子是一种开链甲川桥连四吡咯，在光吸收后，经历双键异构化，随后是一系列热弛豫过程，最终导致蛋白质的功能结构变化。共振拉曼光谱学对理解这些蛋白质的分子功能做出了重大贡献，尽管实验和光谱的解释都代表了相当大的挑战。本文介绍了利用共振拉曼光谱和理论相结合的方法研究光敏色素辅基结构的成就、潜力和局限性。实验方法进行了讨论，特别注意的策略，以克服不必要的光化学和光物理过程时，探测光敏色素的光诱导反应周期的各种状态。光敏色素，包括工程蛋白变体和与同位素标记的四吡咯形成的加合物，最全面的实验数据集，已获得共振拉曼光谱与近红外激发，也允许探测光敏色素晶体没有光诱导的破坏。模型化合物的拉曼光谱的量子力学计算代表了用于确定蛋白质结合的四吡咯的次甲基桥几何形状的第一近似，并且构成了用于识别特定结构特性的标记带的基础，例如辅因子的质子化状态。这种不可避免地忽略蛋白质环境的理论方法的缺点已经变得明显的三维结构的光敏色素的第一次测定。这些结构模型现在可以用于采用混合方法，结合联合收割机的量子力学和分子力学计算的辅因子和蛋白质矩阵，分别。虽然需要进一步的发展，更准确地描述蛋白质力场，这种方法有望成为一个强大的工具，从拉曼光谱的结构信息的全面提取，这样它可能允许精炼的结构模型的辅因子网站衍生的蛋白质晶体学。(C)2011 Elsevier B.V.保留所有权利。
Phytochromes constitute a family of red-light sensing photoreceptors in plants and microorganisms. The photoactive cofactor is an open-chain methine-bridged tetrapyrrole that, upon light absorption, undergoes a double bond isomerisation followed by series thermal relaxation processes which eventually lead to the functional structural change of the protein. Resonance Raman spectroscopy has contributed significantly to the understanding of the molecular functioning of these proteins although both the experiments and the interpretation of the spectra represent a considerable challenge. This account is dedicated to describe achievements, potential and limitations of combined resonance Raman spectroscopic and theoretical approaches for elucidating cofactor structures in phytochromes. Experimental approaches are discussed paying specific attention on strategies to overcome unwanted photochemical and photophysical processes when probing the various states of the photoinduced reaction cycle of phytochromes. The most comprehensive set of experimental data on phytochromes, including engineered protein variants and adducts formed with isotopically labelled tetrapyrroles, has been obtained by resonance Raman spectroscopy with near-infrared excitation that also allows probing phytochrome crystals without photo-induced destruction. Quantum mechanical calculations of Raman spectra of model compounds represent a first approximation for determining the methine bridge geometry of the protein-bound tetrapyrroles and constitute the basis for the identification of marker bands for specific structural properties such as the protonation state of the cofactor. Drawbacks of this theoretical method that inevitably neglects the protein environment have become evident with the first determinations of three-dimensional structures of phytochromes. These structural models can now be used for employing hybrid methods that combine quantum mechanical and molecular mechanics calculations of the cofactor and the protein matrix, respectively. Although further developments are required for a more accurate description of the protein force field, this methodology promises to become a powerful tool for a comprehensive extraction of structural information from the Raman spectra such it may allow refining structural models of the cofactor site derived by protein crystallography. (C) 2011 Elsevier B.V. All rights reserved.