Browsing by Author "Hung, Chih-Chang"

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Schiff Base Proton Acceptor Assists Photoisomerization of Retinal Chromophores in Bacteriorhodopsin
(2017-06-20)
Hung, Chih-Chang
;
Chen, Xiao-Ru
;
Ko, Ying-Kuan
;
Kobayashi, Takayoshi
;
Yang, Chii-Shen
In this study, we investigated the ultrafast dynamics of bacteriorhodopsins (BRs) from Haloquadratum walsbyi (HwBR) and Haloarcula marismortui (HmBRI and HmBRII). First, the ultrafast dynamics were studied for three HwBR samples: wild-type, D93N mutation, and D104N mutation. The residues of the D93 and D104 mutants correspond to the control by the Schiff base proton acceptor and donor of the proton translocation subchannels. Measurements indicated that the negative charge from the Schiff base proton acceptor residue D93 interacts with the ultrafast and substantial change of the electrostatic potential associated with chromophore isomerization. By contrast, the Schiff base proton donor assists the restructuring of the chromophore cavity hydrogen-bond network during the thermalization of the vibrational hot state. Second, the ultrafast dynamics of the wild-types of HwBR, HmBRI, and HmBRII were compared. Measurements demonstrated that the hydrogen-bond network in the extracellular region in HwBR and HmBRII slows the photoisomerization of retinal chromophores, and the negatively charged helices on the cytoplasmic side of HwBR and HmBRII accelerate the thermalization of the vibrational hot state of retinal chromophores. The similarity of the correlation spectra of the wild-type HmBRI and D104N mutant of HwBR indicates that inactivation of the Schiff base proton donor induces a positive charge on the helices of the cytoplasmic side.
Ultrafast dynamics of ligand and substrate interaction in endothelial nitric oxide synthase under Soret excitation
(2016-07-08)
Hung, Chih-Chang
;
Yabushita, Atsushi
;
Kobayashi, Takayoshi
;
Chen, Pei-Feng
;
Liang, Keng S.
Ultrafast transient absorption spectroscopy of endothelial NOS oxygenase domain (eNOS-oxy) was performed to study dynamics of ligand or substrate interaction under Soret band excitation. Photo-excitation dissociates imidazole ligand in <300 fs, then followed by vibrational cooling and recombination within 2 ps. Such impulsive bond breaking and late rebinding generate proteinquakes, which relaxes in several tens of picoseconds. The photo excited dynamics of eNOS-oxy with L-arginine substrate mainly occurs at the local site of heme, including ultrafast internal conversion within 400 fs, vibrational cooling, charge transfer, and complete ground-state recovery within 1.4 ps. The eNOS-oxy without additive is partially bound with water molecule, thus its photoexcited dynamics also shows ligand dissociation in <800 fs. Then it followed by vibrational cooling coupled with charge transfer in 4.8 ps, and recombination of ligand to distal side of heme in 12 ps. (C) 2016 Elsevier B.V. All rights reserved.
Ultrafast relaxation dynamics of nitric oxide synthase studied by visible broadband transient absorption spectroscopy
(2017-09-01)
Hung, Chih-Chang
;
Yabushita, Atsushi
;
Kobayashi, Takayoshi
;
Chen, Pei-Feng
;
Liang, Keng S.
Ultrafast dynamics of endothelial nitric oxide synthase (eNOS) oxygenase domain was studied by transient absorption spectroscopy pumping at Soret band. The broadband visible probe spectrum has visualized the relaxation dynamics from the Soret band to Q-band and charge transfer (CT) band. Supported by two-dimensional correlation spectroscopy, global fitting analysis has successfully concluded the relaxation dynamics from the Soret band to be (1) electronic transition to Q-band (0.16 ps), (2) ligand dissociation and CT (0.94 ps), (3) relaxation of the CT state (4.0 ps), and (4) ligand rebinding (59 ps). (C) 2017 Elsevier B.V. All rights reserved.