The structures of the active center in dark-adapted bacteriorhodopsin by solution-state NMR spectroscopy.
The two forms of bacteriorhodopsin present in the dark-adapted state, containing either all-trans or 13-cis,15-syn retinal, were examined by using solution state NMR, and their structures were determined. Comparison of the all-trans and the 13-cis,15-syn forms shows a shift in position of about 0.25 A within the pocket of the protein. Comparing this to the 13-cis,15-anti chromophore of the catalytic cycle M-intermediate structure, the 13-cis,15-syn form demonstrates a less pronounced up-tilt of the retinal C12[bond]C14 region, while leaving W182 and T178 essentially unchanged. The N[bond]H dipole of the Schiff base orients toward the extracellular side in both forms, however, it reorients toward the intracellular side in the 13-cis,15-anti configuration to form the catalytic M-intermediate. Thus, the change of the N[bond]H dipole is considered primarily responsible for energy storage, conformation changes of the protein, and the deprotonation of the Schiff base. The structural similarity of the all-trans and 13-cis,15-syn forms is taken as strong evidence for the ion dipole dragging model by which proton (hydroxide ion) translocation follows the change of the dipole.
Patzelt
Heiko
H
Max-Planck-Institut für Biochemie, Abteilung Membranbiochemie, Am Klopferspitz 18a, 82152 Martinsried, Germany;.
Simon
Bernd
B
terLaak
Antonius
A
Kessler
Brigitte
B
Kühne
Ronald
R
Schmieder
Peter
P
Oesterhelt
Dieter
D
Oschkinat
Hartmut
H
D000595:Amino Acid Sequence; D001436:Bacteriorhodopsins / Q000737:chemistry*; D001665:Binding Sites; D003624:Darkness; D009682:Magnetic Resonance Spectroscopy / Q000379:methods; D008958:Models, Molecular; D011487:Protein Conformation
D001436:Bacteriorhodopsins