High-resolution solid-state 13C-NMR study of carbons C-5 and C-12 of the chromophore of bovine rhodopsin: evidence for a 6-S-cis conformation with negative-charge perturbation near C-12

Solid-state 13C magic-angle spinning NMR spectroscopy has been employed to study the conformation of the 11-cis-retinylidene Schiff base chromophore in bovine rhodopsin. Spectra were obtained from lyophilized samples of bovine rhodopsin selectively 13C-labeled at position C-5 or C-12 of the retinyl moiety, and reconstituted in the fully saturated branched-chain phospholipid diphytanoyl glycerophosphocholine. Comparison of the NMR parameters for carbon C-5 presented in this paper with those published for retinyl Schiff base model compounds and bacteriorhodopsin by Harbison and coworkers [Harbison et al. (1985) Biochemistry 24, 6955-6962], indicate that in bovine rhodopsin the C-6-C-7 single bond has the unperturbed cis conformation. This is in contrast to the 6-S-trans conformation found in bacteriorhodopsin. The NMR parameters for bovine [12-13C]rhodopsin present evidence for the presence of a negative charge interacting with the retinyl moiety near C-12, in agreement with the model for the opsin shift presented by Honig and Nakanishi and coworkers [Kakitani et al. (1985) Photochem. Photobiol. 41, 471-479].