PHOTOEXCITATION OF RHODOPSIN: CONFORMATION CHANGES IN THE CHROMOPHORE, PROTEIN AND ASSOCIATED LIPIDS AS DETERMINED BY FTIR DIFFERENCE SPECTROSCOPY |
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| Authors: | Willem J DeGrip Daniel Gray John Gillespie Petra H M Bovee Ellen M M Van Den Berg Johan Lugtenburg Kenneth J Rothschild † |
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| Institution: | Department of Biochemistry, Center for Eye Research, University of Nijmegen, 6500 HB, Nijmegen, The Netherlands;department of Physics and Program in Cellular Biophysics, Boston University, Boston, MA 02215, USA;0Department of Organic Chemistry, Gorlaeus Laboratories, University of Leiden, 2300 RA Leiden, The Netherlands |
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| Abstract: | Abstract— The visual pigment rhodopsin is the major membrane protein in the rod photoreceptor membrane. Rhodopsin's function is to transduce the light induced isomerization (ll-cis to all-trans) of its internally located retinylidene chromophore into transient expression of signal sites at the surface of the protein. Fourier transform infrared (FTIR) difference spectroscopy has been used to study all of the steps in the photobleaching sequence of rhodopsin. Early protein alterations involving the peptide backbone and aspartic and/or glutamic carboxyl groups were detected which increase upon lumirhodopsin formation and spread to water exposed carboxyl groups by metarhodopsin II. The intensified and frequency shifted hydrogen-out-of-plane vibrations of the chromophore that are present in bathorhodopsin are absent in lumirhodopsin. This indicates that by lumirhodopsin, the chromophore has relaxed relative to its more strained all-frans form in bathorhodopsin. Finally, the transition to metarhodopsin II is found to involve perturbation of the acyl tail region of unsaturated phospholipid molecules possibly in response to small changes in the shape of the rhodopsin. |
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