PMID: 12119389

Authors:

Patzelt H, Simon B, terLaak A, Kessler B, Kuhne R, Schmieder P, Oesterhelt D, Oschkinat H

Title:

The structures of the active center in dark-adapted bacteriorhodopsin by solution-state NMR spectroscopy.

Journal:

Proc Natl Acad Sci U S A. 2002 Jul 23;99(15):9765-70. Epub 2002 Jul 15.

Abstract:

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.