Department of Chemistry, University of Southern California, Los Angeles, California 90089-0482, United States.
J Phys Chem B. 2011 Jun 30;115(25):8296-303. doi: 10.1021/jp2020269. Epub 2011 Jun 6.
The effect of the protein environment on the electronic structure of the green fluorescent protein (GFP) chromophore is investigated by QM/MM (quantum mechanics/molecular mechanics) calculations. The protein has very small effect on the excitation energy of the bright absorbing and the lowest triplet states of the anionic GFP chromophore, deprotonated 4-hydroxybenzylidene-2,3-dimethylimidazolinone (HBDI) anion, however, it increases vertical detachment energy from 2.5 eV (gas-phase deprotonated HBDI anion) to 5.0 eV (solvated protein). We also investigated possible existence of the charge-transfer-to-solvent (CTTS) states associated with the GFP chromophore. Although precursors of such states appear in cluster calculations, a tightly packed structure of the protein prevents the formation of the CTTS states in this system. Motivated by a recently discovered new type of photoconversion, oxidative redding, we characterized the redox properties of GFP. The computed standard reduction potential of the anionic form of GFP is 0.47 V (for the GFP(•) + 1e → GFP(-) reaction), and the reduction potential at physiological conditions (pH 7, T = 25 °C) is 0.06 V.
通过量子力学/分子力学（QM/MM）计算研究了蛋白质环境对绿色荧光蛋白（GFP）发色团电子结构的影响。该蛋白质对明亮吸收态和阴离子 GFP 发色团（去质子化的 4-羟基苯亚甲基-2,3-二甲基咪唑啉酮（HBDI）阴离子）的最低三重态的激发能影响很小，然而，它将垂直离解能从 2.5 eV（气相去质子化的 HBDI 阴离子）增加到 5.0 eV（溶剂化的蛋白质）。我们还研究了与 GFP 发色团相关的可能存在的电荷转移到溶剂（CTTS）态。尽管这些态的前体出现在团簇计算中，但蛋白质的紧密堆积结构阻止了 CTTS 态在该体系中的形成。受最近发现的新型光致变色（氧化红化）的启发，我们对 GFP 的氧化还原性质进行了表征。计算出的 GFP 阴离子形式的标准还原电位为 0.47 V（对于 GFP(•) + 1e → GFP(-) 反应），在生理条件下（pH 7，T = 25 °C）的还原电位为 0.06 V。
