Journal
BIOCHEMISTRY
Volume 43, Issue 34, Pages 10867-10876Publisher
AMER CHEMICAL SOC
DOI: 10.1021/bi0400148
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- NEI NIH HHS [R01 EY002051, R37 EY002051, R01 EY002051-28, EY02051] Funding Source: Medline
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The vibrational structure of the chromophore in the primary photoproduct of vision, bathorhodopsin, is examined to determine the cause of the anomalously decoupled and intense C-11= C-12 hydrogen-out-of-plane (HOOP) wagging modes and their relation to energy storage in the primary photoproduct. Low-temperature (77 K) resonance Raman spectra of Glu181 and Ser186 mutants of bovine rhodopsin reveal only mild mutagenic perturbations of the photoproduct spectrum suggesting that dipolar, electrostatic, or steric interactions with these residues do not cause the HOOP mode frequencies and intensities. Density functional theory calculations are performed to investigate the effect of geometric distortion on the HOOP coupling. The decoupled HOOP modes can be simulated by imposing similar to40degrees twists in the same direction about the C-11=C-12 and C-12-C-13 bonds. Sequence comparison and examination of the binding site suggests that these distortions are caused by three constraints consisting of an electrostatic anchor between the protonated Schiff base and the Glu 113 counterion, as well as steric interactions of the 9- and 13-methyl groups with surrounding residues. This distortion stores light energy that is used to drive the subsequent protein conformational changes that activate rhodopsin.
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