title: Crystal structure of the 13-cis isomer of bacteriorhodopsin in the dark-adapted state.
abstract: The atomic structure of the trans isomer of bacteriorhodopsin was determined previously by using a 3D crystal belonging to the space group P622. Here, a structure is reported for another isomer with the 13-cis, 15-syn retinal in a dark-adapted crystal. Structural comparison of the two isomers indicates that retinal isomerization around the C13[double bond]C14 and the C15[double bond]N bonds is accompanied by noticeable displacements of a few residues in the vicinity of the retinal Schiff base and small re-arrangement of the hydrogen-bonding network in the proton release channel. On the other hand, aromatic residues surrounding the retinal polyene chain were found to scarcely move during the dark/light adaptation. This result suggests that variation in the structural rigidity within the retinal-binding pocket is one of the important factors ensuring the stereospecific isomerization of retinal.
authors.affiliation: Department of Physics, Graduate School of Science, Nagoya University, Nagoya 464-8602, Japan.
authors.forename: Taichi
authors.initials: T
authors.lastname: Nishikawa
authors.forename: Midori
authors.initials: M
authors.lastname: Murakami
authors.forename: Tsutomu
authors.initials: T
authors.lastname: Kouyama
mesh_terms: D001436:Bacteriorhodopsins / Q000737:chemistry*; D018360:Crystallography, X-Ray; D003624:Darkness; D004224:Diterpenes; D019617:Halobacterium salinarum / Q000737:chemistry*; D006860:Hydrogen Bonding; D007536:Isomerism; D008958:Models, Molecular; D010777:Photochemistry; D012172:Retinaldehyde / Q000737:chemistry*
chemical_list: D004224:Diterpenes; C031338:13-cis-retinal; D001436:Bacteriorhodopsins; D012172:Retinaldehyde