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Retinal ligand mobility explains internal hydration and reconciles active rhodopsin structures.
Nicholas Leioatts1, Blake Mertz, Karina Martínez-Mayorga
1Department of Biochemistry and Biophysics, University of Rochester Medical Center , Rochester, New York 14642, United States.
Biochemistry
|December 17, 2013
Summary
Rhodopsin activation involves significant changes in retinal flexibility and water influx into the protein core. These findings clarify the transition from dark to active states, crucial for understanding G-protein-coupled receptors.
Area of Science:
- Biochemistry
- Structural Biology
- Molecular Biophysics
Background:
- Rhodopsin, a key G-protein-coupled receptor (GPCR), mediates dim-light vision.
- Understanding GPCR activation mechanisms is vital due to their pharmaceutical importance.
- Recent structural data offers insights, but rhodopsin activation mechanisms remain incompletely understood.
Purpose of the Study:
- To elucidate the molecular mechanisms underlying the transition of rhodopsin from its inactive (dark) state to the active metarhodopsin I (Meta I) state.
- To investigate the role of ligand flexibility and water dynamics in rhodopsin activation.
Main Methods:
- Microsecond-scale all-atom molecular dynamics (MD) simulations.
- Solid-state (2)H nuclear magnetic resonance (NMR) spectroscopy for validation.
Main Results:
- Significant differences in retinal ligand flexibility between dark and Meta I states were observed.
- Retinal adopts a more elongated conformation in Meta I, consistent with active crystal structures.
- This conformational change correlates with substantial water influx into the protein's hydrophobic core and a shift in the conserved Trp265 residue.
Conclusions:
- Enhanced retinal flexibility upon light activation explains varied retinal orientations in active rhodopsin crystal structures.
- The influx of water and the Trp265 transition are key events in rhodopsin activation.
- These findings provide a deeper mechanistic understanding of GPCR activation dynamics.
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