Time Resolved EPR Study on the Photoinduced Long-Range Charge-Separated State in Protein: Electron Tunneling Mediated by Arginine Residue in Human Serum Albumin.
To elucidate how local molecular conformations play a role on electronic couplings for the long-range photoinduced charge-separated (CS) states in protein systems, we have analyzed time-resolved electron paramagnetic resonance (TREPR) spectra by polarized laser irradiations of 9,10-anthraquinone-1-sulfonate (AQ1S(-)) bound to human serum albumin (HSA). Analyses of the magnetophotoselection effects on the EPR spectra and a docking simulation clarified the molecular geometry and the electronic coupling of the long-range CS states of AQ1S(•2-)-tryptophan214 radical cation (W214(•+)) separated by 1.2 nm. The ligand of AQ1S(-) has been demonstrated to be bound to the drug site I in HSA. Molecular conformations of the binding region were estimated by the docking simulations, indicating that an arginine218 (R218(+)) residue bound to AQ1S(•2-) mediates the long-range electron-transfer. The energetics of triad states of AQ1S(•2-)-R218(+)-W214(•+) and AQ1S(-)-R218(•)-W214(•+) have been computed on the basis of the density functional molecular orbital calculations, providing the clear evidence for the long-range electronic couplings of the CS states in terms of the superexchange tunneling model through the arginine residue.
Graduate School of Science and Technology, Shizuoka University , 836 Ohya Suruga-ku, Shizuoka 422-8529, Japan.
Masaaki
M
Fuki
Graduate School of Science and Technology, Shizuoka University , 836 Ohya Suruga-ku, Shizuoka 422-8529, Japan.
Hisao
H
Murai
Department of Chemistry, Graduate School of Science, Kobe University , 1-1 Rokkoudai-cho, Nada-ku, Kobe 657-8501, Japan.
Takashi
T
Tachikawa
Department of Chemistry, Graduate School of Science, Kobe University , 1-1 Rokkoudai-cho, Nada-ku, Kobe 657-8501, Japan.
Yasuhiro
Y
Kobori
D000880:Anthraquinones / Q000737:chemistry / Q000378:metabolism; D001120:Arginine / Q000737:chemistry*; D001665:Binding Sites; D004578:Electron Spin Resonance Spectroscopy; D006801:Humans; D007834:Lasers; D062105:Molecular Docking Simulation; D011485:Protein Binding; D000075462:Serum Albumin, Human / Q000737:chemistry* / Q000378:metabolism
D000880:Anthraquinones; C042834:9,10-anthraquinone; D001120:Arginine; D000075462:Serum Albumin, Human