XVIth International Workshop on
Quantum Systems in
Chemistry and Physics
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Excited states of photo-functional proteins: SAC-CI study
Jun-ya Hasegawa
Department of Synthetic Chemistry and Biological Chemistry, Graduate School of Engineering, Kyoto University
In the vision and fluorescent proteins, controlling photo-absorption/emission energy of chromophore is the essential to furnish a protein with the photo-functionality. Retinal Schiff base in vision, luciferin in insects, and green-fluorescent protein chromophores in a jellyfish are the representative compounds in nature. Depending on the molecular interactions with protein environment, these chromophores show a variety of photo-absorption/emission energies.

The present talk summarizes some recent theoretical studies on the spectral tuning mechanism in photobiology using quantum chemical calculations with the symmetry-adapted cluster configuration interaction (SAC-CI) method. SAC-CI is a coupled-cluster method for describing the electron correlations in the ground and excited states. To investigate excited states of chromophores and fluorophores in proteins, we introduced the SAC-CI method into the QM/MM framework.

We studied spectral tuning mechanism of retinal proteins [1] and emission color tuning of firefly luciferase [2] and fluorescent proteins [3], and found a common feature in their physical origin. Analyzing molecular interactions, we could also clarify amino acidsí contributions to the spectral tuning. On the basis of the mechanisms, we proposed mutations for artificially controlling the color of proteins, which was computationally examined by computational simulations [2,3].

[1] K. Fujimoto, J. Hasegawa, H. Nakatsuji, Bull. Chem. Soc. Jpn., 82 (2009) 1140-1148. [2] N. Nakatani, J. Hasegawa, H. Nakatsuji, J. Am. Chem. Soc. 129 (2007) 8756-8765; N. Nakatani, J. Hasegawa, and H. Nakatsuji, Chem. Phys. Letters 469 (2009) 191-194. [3] J. Hasegawa, T. Ise, K. Fujimoto, A. Kikuchi, E. Fukumura, A. Miyawaki, and Y. Shiro, J. Phys. Chem. B, 114(8), 2971-2979 (2010).


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