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.
Department of Physiology and Biophysics, University of California, Irvine, California, USA.
Deliang
D
Chen
Janos K
JK
Lanyi
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