Bacteriorhodopsin By xray-crystallographic analysis |
Part 1 (next) |
| Bacteriorhodopsin is an all-alpha-helix membrane protein with seven transmembrane spans. It is found as a trimer in the purple membranes of Halobacteria. It is a light-driven proton pump. The protein is shown in blue, except for lysine 216 and the covalently-attached retinal in yellow, and the phospholipids shown in CPK. Notice that the retinal is almost completely buried between the alpha-helices.
The protein is now shown in Cartoons, with Lys 216+Retinal in yellow, Asp 96 in red, and Asp 85 in orange. These are the three key players in proton transport.
When the retinal absorbs a photon of light, it isomerizes, and releases a proton. Asp 85 helps to shuttle the proton to the outside, while Asp 96 helps to pass a proton back to the relaxed retinal. Aromatic residues: Trp and Tyr, shown in green, and Phe shown in white. These residues are found clustered in many membrane proteins. They are found primarily in the alpha-helices, near the two membrane surfaces, and at sites of protein-protein contact. Proline residues are shown in green. They are found in the loops, at the N-termini of the alpha-helices, and 3 are found within alpha-helices. Each is associated with a kink of 16-24 degrees. Gly residues, shown in green, spacefilling, are found in loops, at helix-helix contacts, and at the C-termini of alpha-helices.Author, title, referenceļ¼PubMed) 2brd (PDB) |