In our eyes, rhodopsin uses the molecule retinal to see light
Opsin as GPCR
Completing the Cycle
Exploring the Structure
Rhodopsin (PDB entries 1u19, 3pqr and 3cap)
The visual cycle has been studied in great detail using spectroscopic methods, and researchers have discovered that rhodopsin goes through many steps after it absorbs light. Some of these are very subtle: for instance, the change from cis to trans retinal is extremely fast, but the protein takes a bit more time to catch up, creating some observable intermediate states. The changes that lead to the nerve signal, however, are more significant. The two crystal structures shown here show two important steps: the first is rhodopsin before it absorbs light (PDB entry 1u19 ) and the second is after light has been absorbed and protein has shifted into the shape recognized by G-proteins (PDB entry 3pqr ). To look at these structures more detail, as well as the structure of opsin after retinal has been removed (PDB entry 3cap ), click on the image for an interactive Jmol.
Topics for Further Discussion
- You can use the Structure Comparison tool to explore the similarity of opsin and G-protein-coupled receptors.
- Many structures are available for intermediate states of rhodopsin in its visual cycle. They have been given unusual names like photorhodopsin, bathorhodopsin, lumirhodopsin, and Meta II (shown in the Jmol). You can use the Structure Comparison tool to explore the motion of the protein as it moves through these states.
March 2012, David Goodselldoi:10.2210/rcsb_pdb/mom_2012_3