Electron crystallography reveals the structure of metarhodopsin I.
Rhodopsin is the prototypical G protein-coupled receptor, responsible for detection of dim light in vision. Upon absorption of a photon, rhodopsin undergoes structural changes, characterised by distinct photointermediates. Currently, only the ground-state structure has been described. We have determined a density map of a photostationary state highly enriched in metarhodopsin I, to a resolution of 5.5 A in the membrane plane, by electron crystallography. The map shows density for helix 8, the cytoplasmic loops, the extracellular plug, all tryptophan residues, an ordered cholesterol molecule and the beta-ionone ring. Comparison of this map with X-ray structures of the ground state reveals that metarhodopsin I formation does not involve large rigid-body movements of helices, but there is a rearrangement close to the bend of helix 6, at the level of the retinal chromophore. There is no gradual build-up of the large conformational change known to accompany metarhodopsin II formation. The protein remains in a conformation similar to that of the ground state until late in the photobleaching process.
MRC Laboratory of Molecular Biology, Cambridge, UK.
Jonathan J
JJ
Ruprecht
Thorsten
T
Mielke
Reiner
R
Vogel
Claudio
C
Villa
Gebhard F X
GF
Schertler
D000818:Animals; D002417:Cattle; D020285:Cryoelectron Microscopy; D018360:Crystallography, X-Ray; D008958:Models, Molecular; D011487:Protein Conformation; D012243:Rhodopsin / Q000737:chemistry*; D012374:Rod Cell Outer Segment / Q000737:chemistry
C013110:metarhodopsins; D012243:Rhodopsin