Li Zhuo, Robinson David, Hirst Jonathan D
School of Chemistry, University of Nottingham, Nottingham NG7 2RD, UK.
Faraday Discuss. 2015;177:329-44. doi: 10.1039/c4fd00163j.
The Franck-Condon effect is considered and the vibrational structure of the πnbπ* transition of the peptide backbone is incorporated into matrix method calculations of the electronic circular dichroism (CD) spectra of proteins in the far-ultraviolet. We employ the state-averaged CASPT2 method to calculate the ground and πnbπ* excited state geometries and frequencies of N-methylacetamide (NMA), which represents the peptide chromophore. The results of these calculations are used to incorporate vibronic levels of the excited states into the matrix method calculation. The CD spectra of a set of 49 proteins, comprising a range of structural types, are calculated to assess the influence of the vibrational structure. The calculated spectra of α-helical proteins are better resolved using the vibronic parameters and correlation between the experimental and the calculated intensity of less regular β structure proteins improves over most wavelengths in the far-UV. No obvious improvement is observed in the calculated spectra of regular β-sheet proteins. Our high-level ab initio calculations of the vibronic structure of the πnbπ* transition in NMA have provided some further insight into the physical origins of the nature of protein CD spectra in the far-UV.
考虑了弗兰克-康登效应，并将肽主链πnbπ跃迁的振动结构纳入远紫外区蛋白质电子圆二色性（CD）光谱的矩阵方法计算中。我们采用状态平均的CASPT2方法来计算N-甲基乙酰胺（NMA）的基态和πnbπ激发态几何结构及频率，NMA代表肽发色团。这些计算结果用于将激发态的振转能级纳入矩阵方法计算中。计算了一组包含多种结构类型的49种蛋白质的CD光谱，以评估振动结构的影响。使用振转参数可以更好地分辨α-螺旋蛋白质的计算光谱，并且在远紫外区的大多数波长上，不太规则的β结构蛋白质的实验强度与计算强度之间的相关性有所改善。在规则β-折叠蛋白质的计算光谱中未观察到明显改善。我们对NMA中πnbπ*跃迁振转结构的高水平从头计算，为深入了解远紫外区蛋白质CD光谱性质的物理起源提供了一些进一步的见解。
