Rischel C, Spiedel D, Ridge J P, Jones M R, Breton J, Lambry J C, Martin J L, Vos M H
Institut National de la Santé et de la Recherche Médicale U451, Laboratoire d'Optique Appliquée, Ecole Polytechnique-Ecole Nationale Supérieure de Techniques Avancées, F-91761 Palaiseau Cedex, France.
Proc Natl Acad Sci U S A. 1998 Oct 13;95(21):12306-11. doi: 10.1073/pnas.95.21.12306.
As a step toward understanding their functional role, the low frequency vibrational motions (<300 cm-1) that are coupled to optical excitation of the primary donor bacteriochlorophyll cofactors in the reaction center from Rhodobacter sphaeroides were investigated. The pattern of hydrogen-bonding interaction between these bacteriochlorophylls and the surrounding protein was altered in several ways by mutation of single amino acids. The spectrum of low frequency vibrational modes identified by femtosecond coherence spectroscopy varied strongly between the different reaction center complexes, including between different mutants where the pattern of hydrogen bonds was the same. It is argued that these variations are primarily due to changes in the nature of the individual modes, rather than to changes in the charge distribution in the electronic states involved in the optical excitation. Pronounced effects of point mutations on the low frequency vibrational modes active in a protein-cofactor system have not been reported previously. The changes in frequency observed indicate a strong involvement of the protein in these nuclear motions and demonstrate that the protein matrix can increase or decrease the fluctuations of the cofactor along specific directions.
作为理解其功能作用的一个步骤，对与球形红细菌反应中心初级供体细菌叶绿素辅因子的光激发相耦合的低频振动运动（<300 cm-1）进行了研究。通过单个氨基酸的突变，这些细菌叶绿素与周围蛋白质之间的氢键相互作用模式在几个方面发生了改变。飞秒相干光谱法识别出的低频振动模式光谱在不同的反应中心复合物之间有很大差异，包括在氢键模式相同的不同突变体之间。有人认为，这些变化主要是由于各个模式性质的改变，而不是由于光激发所涉及的电子态中电荷分布的变化。此前尚未报道点突变对蛋白质-辅因子系统中活跃的低频振动模式有明显影响。观察到的频率变化表明蛋白质强烈参与了这些核运动，并证明蛋白质基质可以增加或减少辅因子沿特定方向的波动。
