Characterization and Photochemistry of 13-Desmethyl Bacteriorhodopsin
| Autor: | Charles H. Buck, Nathan B. Gillespie, Jeffrey A. Stuart, Lei Ren, Robert R. Birge, Karissa A. Utzat, Heather W. Daniell, Deborah Dews, Lavoisier Ramos |
|---|---|
| Rok vydání: | 2005 |
| Předmět: |
Photochemistry
Infrared Spectrum Analysis Raman Article Retina symbols.namesake chemistry.chemical_compound Spectroscopy Fourier Transform Infrared Materials Chemistry Molecule Physical and Theoretical Chemistry Spectroscopy Molecular Structure biology Chemistry Molecular orbital theory Bacteriorhodopsin Retinal Models Theoretical Chromophore Surfaces Coatings and Films Kinetics Bacteriorhodopsins symbols biology.protein Protons Raman spectroscopy Hydrogen |
| Zdroj: | The Journal of Physical Chemistry B. 109:16142-16152 |
| ISSN: | 1520-5207 1520-6106 |
| Popis: | The photochemistry of the 13-desmethyl (DM) analogue of bacteriorhodopsin (BR) is examined by using spectroscopy, molecular orbital theory, and chromophore extraction followed by conformational analysis. The removal of the 13-methyl group permits the direct photochemical formation of a thermally stable, photochemically reversible state, P1(DM) (lambda(max) = 525 nm), which can be generated efficiently by exciting the resting state, bR(DM) with yellow or red light (lambda590 nm). Chromophore extraction analysis reveals that the retinal configuration in P1(DM) is 9-cis, identical to that of the retinal configuration in the native BR P1 state. Fourier transform infrared and Raman experiments on P1(DM) indicate an anti configuration around the C15=N bond, as would be expected of an O-state photoproduct. However, low-temperature spectroscopy and ambient, time-resolved studies indicate that the P1(DM) state forms primarily via thermal relaxation from the L(D)(DM) state. Theoretical studies on the BR binding site show that 13-dm retinal is capable of isomerizing into a 9-cis configuration with minimal steric hindrance from surrounding residues, in contrast to the native chromophore in which surrounding residues significantly obstruct the corresponding motion. Analysis of the photokinetic experiments indicates that the Arrhenius activation energy of the bR(DM) --P1(DM) transition in 13-dm-BR is less than 0.6 kcal/mol (vs 22 +/-5 kcal/mol measured for the bR --P (P1 and P2) reaction in 85:15 glycerol:water suspensions of wild type). Consequently, the P1(DM) state in 13-dm-BR can form directly from all-trans, 15-anti intermediates (bR(DM) and O(DM)) or all-trans, 15-syn (K(D)(DM)/L(D)(DM)) intermediates. This study demonstrates that the 13-methyl group, and its interactions with nearby binding site residues, is primarily responsible for channeling one-photon photochemical and thermal reactions and is limited to the all-trans and 13-cis species interconversions in the native protein. |
| Databáze: | OpenAIRE |
| Externí odkaz: |
|