Structural constraints imposed by a non-native disulfide cause reversible changes in rhodopsin photointermediate...

Area of Science:

• Biochemistry
• Molecular Biology
• Photochemistry

Background:

• Rhodopsin, a G protein-coupled receptor, initiates visual signal transduction.
• Understanding rhodopsin activation intermediates is crucial for visual neuroscience.
• Specific disulfide bonds can modulate protein function and stability.

Purpose of the Study:

• To investigate the effect of a specific disulfide bridge (Cys140-Cys222) on bovine rhodopsin activation kinetics.
• To explore the utility of disulfide bond formation as a tool to differentiate rhodopsin intermediates.
• To gain insights into the structural differences between meta I intermediates.

Main Methods:

• Bovine rhodopsin was suspended in lauryl maltoside detergent.
• A disulfide bridge was formed between Cys140 and Cys222 using Cu(phen)(3)(2+).
• Absorption difference spectra were recorded after 477 nm light excitation over a time scale from 1 microsecond to 690 milliseconds.
• Kinetic data were analyzed using global exponential fitting.

Main Results:

• Rhodopsin with the Cys140-Cys222 disulfide bridge required only two exponential components for kinetic fitting, unlike untreated or reduced rhodopsin (three components).
• Cu(phen)(3)(2+) treatment favored the meta I(380) intermediate over meta I(480) and slowed meta II formation from meta I(380).
• Dithiothreitol reduction of non-oxidized rhodopsin did not affect observed kinetics.

Conclusions:

• Formation of the Cys140-Cys222 disulfide bridge in rhodopsin alters its activation kinetics.
• This disulfide bond formation serves as a valuable tool to discriminate between distinct rhodopsin activation intermediates.
• The findings suggest structural similarities between the meta I(380) intermediate and the constraint imposed by the Cys140-Cys222 disulfide bridge.