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Conformational motion in bacteriorhodopsin: the K to L transition
1Department of Chemistry, University of Kansas, Lawrence 66045.
Biochemistry
|January 15, 1991
Summary
Conformational motion in bacteriorhodopsin was detected by comparing linear dichroism and transient absorption. This motion, linked to the L550 intermediate, occurs on a 1.7-microsecond timescale during the photocycle.
Area of Science:
- Biophysics
- Photochemistry
- Structural Biology
Background:
- Bacteriorhodopsin is a light-driven proton pump crucial for energy transduction.
- Understanding its photocycle dynamics is key to elucidating energy conversion mechanisms.
Purpose of the Study:
- To detect and characterize protein conformational motion during the early stages of the bacteriorhodopsin photocycle.
- To differentiate between chromophore electronic transitions and protein structural rearrangements.
Main Methods:
- Time-resolved linear dichroism spectroscopy.
- Time-resolved transient absorption spectroscopy.
- Analysis of K610 and L550 intermediates in bacteriorhodopsin.
Main Results:
- Transient absorption revealed lifetimes of K610 and L550 intermediates, unaffected by conformational motion.
- Linear dichroism detected orientational motion of the chromophore with a 1.7-microsecond rotational time constant.
- Wavelength dependence confirmed this motion is associated with the L550 intermediate.
Conclusions:
- Protein conformational motion occurs within the first 10 microseconds of the bacteriorhodopsin photocycle.
- This motion is primarily linked to the L550 intermediate, indicating a significant structural change.
- No orientational motion was observed on the timescale of the L550 to M410 transition.