Structural changes in the N and N' states of the bacteriorhodopsin photocycle.
The bacteriorhodopsin transport cycle includes protonation of the retinal Schiff base by Asp96 (M-->N reaction) and reprotonation of Asp96 from the cytoplasmic surface (N-->N' reaction). We measured distance changes between pairs of spin-labeled structural elements of interest, and in general observed larger overall structural changes in the N state compared with the N' state. The distance between the C-D loop and E-F interhelical loops in A103R1/M163R1 increased approximately 6 A in the N state and approximately 3 A in the N' state. The opposite trend of distance changes in V101R1/A168R1 and L100R1/T170R1 supports counterclockwise rotation of helix F in the N but not the N' state. Small distance increases were observed in S169R1/S226R1, but little change was seen in G106R1/G155R1. Taking earlier published EPR data into account, we suggest that structural changes of the E-F loop occur first, and then helices F and G begin to move together in the late M state. These motions then reach their maximum amplitude in the N state, evidently to facilitate the release of a proton from Asp96 and the formation of a proton-conduction pathway from Asp96 to the Schiff base. The structural changes reverse their directions and decay in the N' state.
Chen
Deliang
D
Department of Physiology and Biophysics, University of California, Irvine, California, USA.
Lanyi
Janos K
JK
D001436:Bacteriorhodopsins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D008027:Light; D008958:Models, Molecular; D009154:Mutation; D011487:Protein Conformation / Q000528:radiation effects; D015202:Protein Engineering; D013113:Spin Labels
D013113:Spin Labels; D001436:Bacteriorhodopsins