High-resolution X-ray structure of an early intermediate in the bacteriorhodopsin photocycle.
Bacteriorhodopsin is the simplest known photon-driven proton pump and as such provides a model for the study of a basic function in bioenergetics. Its seven transmembrane helices encompass a proton translocation pathway containing the chromophore, a retinal molecule covalently bound to lysine 216 through a protonated Schiff base, and a series of proton donors and acceptors. Photoisomerization of the all-trans retinal to the 13-cis configuration initiates the vectorial translocation of a proton from the Schiff base, the primary proton donor, to the extracellular side, followed by reprotonation of the Schiff base from the cytoplasm. Here we describe the high-resolution X-ray structure of an early intermediate in the photocycle of bacteriorhodopsin, which is formed directly after photoexcitation. A key water molecule is dislocated, allowing the primary proton acceptor, Asp 85, to move. Movement of the main-chain Lys 216 locally disrupts the hydrogen-bonding network of helix G, facilitating structural changes later in the photocycle.
Edman
K
K
Department of Biochemistry, Uppsala University, Biomedical Centre, Sweden.
Nollert
P
P
Royant
A
A
Belrhali
H
H
Pebay-Peyroula
E
E
Hajdu
J
J
Neutze
R
R
Landau
E M
EM
D001436:Bacteriorhodopsins / Q000737:chemistry* / Q000378:metabolism; D018360:Crystallography, X-Ray; D008027:Light; D008958:Models, Molecular; D008969:Molecular Sequence Data; D010777:Photochemistry
D001436:Bacteriorhodopsins