Time-resolved photointermediate changes in rhodopsin glutamic acid 181 mutants

Area of Science:

• Biochemistry
• Molecular Biology
• Photochemistry

Background:

• Rhodopsin, a G protein-coupled receptor, plays a vital role in vision.
• The retinylidene chromophore pocket is essential for rhodopsin's light-sensing ability.
• Understanding the role of specific amino acids, like glutamic acid 181, is key to elucidating rhodopsin activation mechanisms.

Purpose of the Study:

• To investigate the functional role of glutamic acid 181 (E181) in the bovine rhodopsin chromophore pocket.
• To determine how mutations at E181 affect the dynamics and spectral properties of early photointermediates.
• To assess the contribution of E181 to receptor activation and Schiff base deprotonation.

Main Methods:

• Expression of E181 mutants of bovine rhodopsin in COS cells.
• Spectroscopic analysis of lauryl maltoside pigment suspensions using 7 ns laser pulses.
• Time-resolved absorbance measurements to monitor photointermediate decay and spectral shifts.

Main Results:

• Most E181 mutants exhibited accelerated bathorhodopsin decay compared to wild type.
• E181D mutant showed an unusual blue shift in the bathorhodopsin decay product (BSI).
• Mutations significantly affected the lumirhodopsin I to lumirhodopsin II transition, altering spectral shifts and Schiff base deprotonation dynamics.

Conclusions:

• Glutamic acid 181 is critical for the early stages of bovine rhodopsin activation.
• The charge and nature of residue 181 influence the stability and spectral characteristics of photointermediates.
• Negative charge at position 181 likely stabilizes the protonated Schiff base in later intermediates.