Ultrafast X-Rays Capture Retinal Traversing Conical Intersection in Rhodopsin

Area of Science:

• Biochemistry
• Structural Biology
• Biophysics

Background:

• G-protein-coupled receptors (GPCRs), specifically the Rhodopsin family, are vital medicinal targets.
• Understanding the activation mechanism of visual rhodopsin, particularly the role of retinal cofactor dynamics, is crucial but remains unclear.

Purpose of the Study:

• To elucidate the mechanism of rhodopsin activation by observing retinal cofactor dynamics.
• To investigate the role of femtosecond-scale nuclear changes and amino acid movements in transmembrane signaling.

Main Methods:

• Utilized time-resolved X-ray solution scattering with a free-electron laser to capture retinal cis-trans isomerization.
• Employed all-atom simulations to reveal ultrafast amino acid movements.
• Conducted ligand-free opsin measurements to confirm light activation pathways.

Main Results:

• Observed retinal cis-trans isomerization at the conical intersection of excited and ground-state energy surfaces.
• Identified femtosecond-scale nuclear changes initiated by resonant photon absorption.
• Demonstrated that photonic energy is directly transmitted within the protein, independent of non-resonant processes.

Conclusions:

• The study unveils how cofactor dynamics activate rhodopsin through direct photonic energy transmission.
• The employed method overcomes limitations of crystal packing and cryotrapping.
• Provides a novel understanding of GPCR activation mechanisms at an unprecedented timescale.