Lipid-Rhodopsin Hydrophobic Mismatch Alters Rhodopsin Helical Content
The ability of photoactivated rhodopsin to achieve the enzymatically active metarhodopsin II conformation is exquisitely sensitive to bilayer hydrophobic thickness. The sensitivity of rhodopsin to the lipid matrix has been explained by the hydrophobic matching theory, which predicts that lipid bilayers adjust elastically to the hydrophobic length of transmembrane helices. Here, we examined if bilayer thickness adjusts to the length of the protein or if the protein alters its conformation to adapt to the bilayer. Purified bovine rhodopsin was reconstituted into a series of mono-unsaturated phosphatidylcholines with 14-20 carbons per hydrocarbon chain. Changes of hydrocarbon chain length were measured by 2H NMR, and protein helical content was quantified by synchrotron radiation circular dichroism and conventional circular dichroism. Experiments were conducted on dark-adapted rhodopsin, the photo-intermediates metarhodopsin I/II/III, and opsin. Changes of bilayer thickness upon rhodopsin incorporation and photoactivation were mostly absent. In contrast, the helical content of rhodopsin increased with membrane hydrophobic thickness. Helical content did not change measurably upon photoactivation. The increases of bilayer thickness and helicity of rhodopsin are accompanied by higher metarhodopsin II/metarhodopsin I ratios, faster rates of metarhodopsin II formation, an increase of tryptophan fluorescence, and higher temperatures of rhodopsin denaturation. The data suggest a surprising adaptability of this G protein-coupled membrane receptor to properties of the lipid matrix.
- Research Organization:
- Brookhaven National Lab. (BNL), Upton, NY (United States). National Synchrotron Light Source
- Sponsoring Organization:
- Doe - Office Of Science
- DOE Contract Number:
- DE-AC02-98CH10886
- OSTI ID:
- 959781
- Report Number(s):
- BNL-82767-2009-JA; JACSAT; TRN: US1005807
- Journal Information:
- Journal of the American Chemical Society, Vol. 130; ISSN 0002-7863
- Country of Publication:
- United States
- Language:
- English
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