Bacteriorhodopsin (bR), a membrane protein from Halobacterium salinarum, uses light energy to generate a proton-motive force across the cell membrane. After photon absorption by the retinal chromophore, five spectroscopically characterizable intermediates (designated K, L, M, N, and O) are formed in sequence, followed by a return to the resting state, bR568. In the M-state phase of this photocycle there appear to be at least three substates whose visible spectra show little difference, but which can be distinguished by their infrared spectra, by their nuclear magnetic resonance spectra, and by other physical measurements. Bacteriorhodopsin is a 27 kDa integral membrane protein usually found in two-dimensional crystalline patches known as "purple membrane", which can occupy almost 50% of the surface area of the archaeal cell. The repeating element of the hexagonal lattice is composed of three identical protein chains, each rotated by 120 degrees relative to the others. Here you can see a classical X-ray structure of ground-state bacteriorhodopsin from Halobacterium salinarum (PDB code: 1KGB)

#molecularart ... #immolecular ... #bacteriorhodopsin ... #membrane ... #proton ... #pump ... #xray

Structure rendered with @proteinimaging and depicted with @corelphotopaint.