Intramembrane signaling mediated by hydrogen-bonding of water and carboxyl groups in bacteriorhodopsin and rhodopsin.
The light-induced mechanism for proton pumping of bacteriorhodopsin was studied by Fourier transform infrared spectroscopy of the discrete sequential intermediate states, L, M, and N. Attention is focused on L in the early microsecond time range, as a transition state in which the Schiff base forms strong H-bonding with a water molecule coordinated with Asp85. This structure leads to transfer of the Schiff base proton to Asp85 in the L-to-M process, which then triggers proton release from Glu204 to the extracellular surface. H-bonding of Arg82 and water molecules are involved in this process. Chloride can replace Asp85 in the D85T mutant, and this anion will be then transported instead of a proton. In L, structural perturbations are induced also around Asp96, through a string of H-bonding mediated by internal water molecules and peptide carbonyls in helices B and C, and Trp182 in helix F. These may cause the structural changes that occur later in the M-to-N process. Similar interactions, through internal water molecules and the peptide bonds in helices B and C, take place in bovine rhodopsin. They transduce changes across the membrane from the Schiff base to the cytoplasmic surface, where the activation of the transducin occurs.
Maeda
A
A
Department of Biophysics, Graduate School of Science, Kyoto University. maeda@photo2.biophys.kyoto-u.ac.jp
Kandori
H
H
Yamazaki
Y
Y
Nishimura
S
S
Hatanaka
M
M
Chon
Y S
YS
Sasaki
J
J
Needleman
R
R
Lanyi
J K
JK
D000818:Animals; D001436:Bacteriorhodopsins / Q000737:chemistry*; D002417:Cattle; D006860:Hydrogen Bonding; D008565:Membrane Proteins / Q000737:chemistry*; D012243:Rhodopsin / Q000737:chemistry*; D015398:Signal Transduction
D008565:Membrane Proteins; D001436:Bacteriorhodopsins; D012243:Rhodopsin