Electrogenic processes and protein conformational changes accompanying the bacteriorhodopsin photocycle

Abstract

The possible mechanisms of electrogenic processes accompanying proton transport in bacteriorhodopsin are discussed on the basis of recent structural data of the protein. Apparent inconsistencies between experimental data and their interpretation are considered. Special emphasis is placed on the protein conformational changes accompanying the reprotonation of chromophore and proton uptake stage in the bacteriorhodopsin photocycle.

Crystal structure of the D85S mutant of bacteriorhodopsin: model of an O-like photocycle intermediate

“…However, large displacements on the extracellular side have not been previously observed. The O 3 BR transition is one of the slowest in the photocycle 28 , hinting at substantial structural rearrangements necessary to either restore the original hydrogen-bonding network of the ground state to allow reprotonation of the proton release group by Asp85, or, in the hydroxide pumping scheme 29,30 the net transport of a hydroxide ion from the extracellular surface to the Schiff base region.…”

Bacteriorhodopsin. Correspondence of the photocycle and electrogenesis with sites of the molecule

“…The photopotential (∆V) at every stage of the process is directly proportional to the projection (r) of the pathway of the proton movement onto the normal to the mem brane and inversely proportional to the dielectric con stant (ε) of the membrane: ∆V ~ kr/ε. Different phases of this response with the photocycle intermediates and structure of the molecule have been compared in detail earlier [2,3], and this comparison is summarized in the figure with regard to new literature data [5,8,9] and our findings. The file with 1c3w coordinates [10] contains the best current X ray diffraction analysis data on the BR molecule and is widely used in modern studies on BR.…”

Eukaryotic G protein-coupled receptors as descendants of prokaryotic sodium-translocating rhodopsins

“…1e ). Functional and structural studies of the Na + translocating rhodopsins [ 16 , 38 , 40 , 41 , 51 , 59 ] indicate that photoisomerization of the retinal, by twisting the side chain of Lys255, is bound to unplug the Na + -binding site of KR2, cause deprotonation of the Schiff base (as it has been shown in bacteriorhodopsin [ 60 ]), and, concurrently, induce an outward movement of the 6 th helix (F-helix), opening a cleft that is needed for ion translocation across the hydrophobic part of the protein, as in other microbial rhodopsins [ 21 , 61 – 65 ]. The nucleophilic nitrogen atom of the deprotonated Schiff base would thereby provide one more ligand for the Na + ion on its way through KR2.…”