Solid-state 13C NMR detection of a perturbed 6-s-trans chromophore in bacteriorhodopsin.

摘要: Solid-state 13C magic angle sample spinning NMR spectroscopy has been used to study the ionone ring portion of chromophore bacteriorhodopsin. Spectra were obtained from fully hydrated samples regenerated with retinals labeled at positions C-5, C-6, C-7, C-8, and C-18 lyophilized C-9 C-13. C-15-labeled studied in both forms. Three independent parameters (the downfield element C-5 chemical shift tensor, C-8 isotropic shift, longitudinal relaxation time) indicate that a 6-s-trans conformation protein, contrast 6-s-cis is energetically favored for retinoids solution. We also observe an additional 27 ppm middle which provides support existence negatively charged protein residue near C-5. Evidence positive charge possibly counterion negative charge, discussed. On basis these results, we present new model retinal binding site, important implications mechanism "opsin shift" observed