pB2 Intermediate of the Photoactive Yellow Protein: Structure and Excitation Energies

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• 作者：Ya-Wen Hsiao ; Walter Thiel
• 刊名：Journal of Physical Chemistry B
• 出版年：2011
• 出版时间：March 10, 2011
• 年：2011
• 卷：115
• 期：9
• 页码：2097-2106
• 全文大小：1011K
• 年卷期：v.115,no.9(March 10, 2011)
• ISSN：1520-5207

文摘

pB₂ is the last electronically excited intermediate of the photoactive yellow protein (PYP) before it thermally reverts to the dark state. We investigate the structure of pB₂ by quantum refinement and QM/MM methods and compare our results with a previously published crystal structure (1TS6). We find differences in the chromophore geometries, mostly with regard to torsion angles, that lead to a somewhat higher degree of planarity than in 1TS6. Quantum chemical calculations at the DFT/MRCI level show that these geometry changes affect the excitation energies and oscillator strengths for transitions into the two lowest singlet excited states. The DFT/MRCI results for the presently determined structures agree well with the experimental spectrum. A classical molecular dynamics simulation of free water molecules surrounding the fixed-in-space PYP indicates hydrogen bonding between water and the solvent-exposed pB₂ chromophore, since one water molecule is constantly found around the phenolic OH group. Including this additional water molecule in the quantum refinement yields improved electron density maps with a good fit of previously unresolved densities. On the other hand, this extra water molecule has little influence on the chromophore structure and the calculated excitation energies. The overall best pB₂ structure from the present work comes from quantum refinement with electrostatics and with an additional water molecule near the phenolic OH group of the chromophore (model 4).