Virtuelle (Nano) Welten: PDB Molecule of the Month 27: Bacteriorhodopsin

Seeing Light

We also build several forms of rhodopsin and use them in our eyes for seeing light. As in bacteriorhodopsin, our rhodopsin also contains a molecule of retinal. (Bacteriorhodopsin is shown on the left, from PDB entry 1fbb, and rhodopsin from cows is shown on the right, from PDB entry 1f88). Retinal is made in our bodies from retinol, or vitamin A, which is essential in the diet, since we cannot synthesize vitamin A on our own. When it absorbs a photon, the retinal in rhodopsin changes shape from bent to straight--just the opposite of retinal in bacteriorhodopsin! This change of shape then pushes the surrounding protein into a slightly different shape, which is sensed by proteins inside the cell. Then, the message is passed through a cascade of proteins, each sending the message to the next, finally launching a nerve signal to the brain. The process is so sensitive that the eye can sense as few as 5 photons.