Light-induced rotation of a transmembrane alpha-helix in bacteriorhodopsin.
Spin labeling EPR spectroscopy has been used to characterize light-induced conformational changes of bacteriorhodopsin (bR). Pairs of nitroxide spin labels were attached to engineered cysteine residues at strategic positions near the cytoplasmic ends of transmembrane alpha-helices B, F, and G in order to monitor distance changes upon light activation. The EPR analysis of six doubly labeled bR mutants indicates that the cytoplasmic end of helix F not only tilts outwards, but also rotates counter-clockwise during the photocycle. The direction of the rotation of helix F is the opposite of the clockwise rotation previously reported for bovine rhodopsin. The opposite chirality of the F helix rotation in the two systems is perhaps related to the differences in the cis-trans photoisomerization of the retinal in the two proteins. Using time-resolved EPR, we monitored the rotation of helix F also in real time, and found that the signal from the rotation arises concurrently with the reprotonation of the retinal Schiff base.
Xiao
W
W
Department of Chemistry, University of California, Berkeley, CA, 94720, USA.
Brown
L S
LS
Needleman
R
R
Lanyi
J K
JK
Shin
Y K
YK
D000818:Animals; D001426:Bacterial Proteins / Q000737:chemistry / Q000378:metabolism; D001436:Bacteriorhodopsins / Q000737:chemistry* / Q000235:genetics / Q000528:radiation effects*; D002417:Cattle; D002628:Chemoreceptor Cells; D003545:Cysteine / Q000235:genetics / Q000378:metabolism; D004578:Electron Spin Resonance Spectroscopy; D029968:Escherichia coli Proteins; D007700:Kinetics; D008027:Light; D008565:Membrane Proteins / Q000737:chemistry / Q000378:metabolism; D008958:Models, Molecular; D017433:Protein Structure, Secondary; D011956:Receptors, Cell Surface / Q000737:chemistry / Q000378:metabolism; D012243:Rhodopsin / Q000737:chemistry / Q000378:metabolism; D012399:Rotation; D013113:Spin Labels; D013696:Temperature
D001426:Bacterial Proteins; D029968:Escherichia coli Proteins; D008565:Membrane Proteins; D011956:Receptors, Cell Surface; D013113:Spin Labels; C057331:Tar protein, E coli; D001436:Bacteriorhodopsins; D012243:Rhodopsin; D003545:Cysteine