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On-Chip Crystallization and Large-Scale Serial Diffraction at Room Temperature
Published on: March 11, 2022
Rhodopsin photointermediates in two-dimensional crystals at physiological temperatures
Istvan Szundi1, Jonathan J Ruprecht, Jacqueline Epps
1Department of Chemistry and Biochemistry, University of California, Santa Cruz, Santa Cruz, California 95064, USA.
Biochemistry
|April 12, 2006
Summary
Bovine rhodopsin in 2D crystals favors the Meta I photointermediate. Proton uptake is blocked, suggesting a key activation step occurs before Schiff base hydrolysis, impacting GPCR signaling.
Area of Science:
- Biochemistry
- Molecular Biology
- Photochemistry
Background:
- Rhodopsin, a G protein-coupled receptor (GPCR), initiates visual signal transduction.
- Understanding rhodopsin photointermediates is crucial for elucidating GPCR activation mechanisms.
- Previous studies on rhodopsin photointermediates were primarily conducted in native membrane suspensions.
Purpose of the Study:
- To investigate the properties of bovine rhodopsin photointermediates in two-dimensional (2D) crystal suspensions.
- To compare the formation and decay kinetics of photointermediates in crystalline versus native membrane environments.
- To determine the nature of the 380 nm absorbing species and its role in GPCR activation.
Main Methods:
- Time-resolved absorbance spectroscopy using 7 ns laser pulses at varying temperatures (15, 25, 35°C).
- Measurements performed on 2D rhodopsin crystal suspensions at different pH values.
- Kinetic modeling of time-resolved absorbance data.
Main Results:
- The crystalline environment favored the Meta I(480) photointermediate, with faster formation from Lumi at 35°C.
- Decay to a 380 nm absorbing species was less complete in 2D crystals compared to native membranes.
- The 380 nm product showed no anomalous pH dependence, and proton uptake for Meta II formation appeared blocked in 2D crystals.
- Kinetic modeling suggested the 380 nm absorbance arises from an on-pathway GPCR activation intermediate, not early Schiff base hydrolysis.
Conclusions:
- The 2D crystal environment alters rhodopsin photointermediate dynamics, favoring Meta I and blocking a later proton uptake step.
- The 380 nm absorbing species is an on-pathway intermediate in GPCR activation, preceding Schiff base hydrolysis.
- Structural determination of this 380 nm intermediate could provide significant insights into receptor activation.
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