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Structure of the bacteriorhodopsin mutant F219L N intermediate revealed by electron crystallography
Author(s) -
Vonck Janet
Publication year - 2000
Publication title -
the embo journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 7.484
H-Index - 392
eISSN - 1460-2075
pISSN - 0261-4189
DOI - 10.1093/emboj/19.10.2152
Subject(s) - bacteriorhodopsin , crystallography , deprotonation , helix (gastropod) , halobacterium salinarum , molecule , schiff base , conformational change , biology , crystal structure , intermediate state , biophysics , stereochemistry , membrane , chemistry , biochemistry , ion , physics , ecology , organic chemistry , atomic physics , snail
Bacteriorhodopsin is a light‐driven proton pump in halobacteria that forms crystalline patches in the cell membrane. Isomerization of the bound retinal initiates a photocycle resulting in the extrusion of a proton. An electron crystallographic analysis of the N intermediate from the mutant F219L gives a three‐dimensional view of the large conformational change that occurs on the cytoplasmic side after deprotonation of the retinal Schiff base. Helix F, together with helix E, tilts away from the center of the molecule, causing a shift of ∼3 Å at the EF loop. The top of helix G moves slightly toward the ground state location of helix F. These movements open a water‐accessible channel in the protein, enabling the transfer of a proton from an aspartate residue to the Schiff base. The movement of helix F toward neighbors in the crystal lattice is so large that it would not allow all molecules to change conformation simultaneously, limiting the occupancy of this state in the membrane to 33%. This explains photocooperative phenomena in the purple membrane.