Raman Optical Activity Probing Structural Deformations of the 4-Hydroxycinnamyl Chromophore in Photoactive Yellow Protein.
Many biological cofactors, such as light-absorbing chromophores in photoreceptors, contain a π-electron system and are planar molecules. These cofactors are, however, usually nonplanar within a protein environment, and such structural distortions have been shown to be functionally important. Because the nonplanar structure makes the molecule chiral, Raman optical activity (ROA) provides a wealth of stereochemical information about the structural and conformational details of cofactors. The present study applied a near-infrared excited ROA to photoactive yellow protein, a blue light receptor. We successfully obtained the ROA spectra of the 4-hydroxycinnamyl chromophore embedded in a protein environment. Furthermore, calculations of the ROA spectra utilizing density functional theory provide detailed structural information, such as data on out-of-plane distortions of the chromophore. The structural information obtained from the ROA spectra includes the positions of hydrogen atoms, which are usually not detected in the crystal structures of biological samples.
†Department of Chemistry and Applied Chemistry, Graduate School of Science and Engineering, Saga University, Saga 840-8502, Japan.
Takahito
T
Shingae
†Department of Chemistry and Applied Chemistry, Graduate School of Science and Engineering, Saga University, Saga 840-8502, Japan.
Kensuke
K
Kubota
‡Department of Microbiology and Molecular Genetics, Oklahoma State University, Stillwater, Oklahoma 74078, United States.
Masato
M
Kumauchi
§Department of Earth and Space Science, Graduate School of Science, Osaka University, Toyonaka, Osaka 560-0043, Japan.
Fumio
F
Tokunaga
†Department of Chemistry and Applied Chemistry, Graduate School of Science and Engineering, Saga University, Saga 840-8502, Japan.|∥PRESTO, JST, 4-1-8 Honcho Kawaguchi, Saitama 332-0012, Japan.
Masashi
M
Unno
chirality; cofactor; density functional theory; photoreceptor; vibrational spectroscopy