Helix movement is coupled to displacement of the second extracellular loop in rhodopsin activation.
The second extracellular loop (EL2) of rhodopsin forms a cap over the binding site of its photoreactive 11-cis retinylidene chromophore. A crucial question has been whether EL2 forms a reversible gate that opens upon activation or acts as a rigid barrier. Distance measurements using solid-state (13)C NMR spectroscopy between the retinal chromophore and the beta4 strand of EL2 show that the loop is displaced from the retinal binding site upon activation, and there is a rearrangement in the hydrogen-bonding networks connecting EL2 with the extracellular ends of transmembrane helices H4, H5 and H6. NMR measurements further reveal that structural changes in EL2 are coupled to the motion of helix H5 and breaking of the ionic lock that regulates activation. These results provide a comprehensive view of how retinal isomerization triggers helix motion and activation in this prototypical G protein-coupled receptor.
Ahuja
Shivani
S
Department of Physics and Astronomy, Stony Brook University, Stony Brook, New York 11794-5215, USA.
Hornak
Viktor
V
Yan
Elsa C Y
EC
Syrett
Natalie
N
Goncalves
Joseph A
JA
Hirshfeld
Amiram
A
Ziliox
Martine
M
Sakmar
Thomas P
TP
Sheves
Mordechai
M
Reeves
Philip J
PJ
Smith
Steven O
SO
Eilers
Markus
M
D000818:Animals; D002417:Cattle; D002460:Cell Line; D006801:Humans; D008027:Light; D008958:Models, Molecular; D019906:Nuclear Magnetic Resonance, Biomolecular; D011485:Protein Binding; D012172:Retinaldehyde / Q000737:chemistry / Q000378:metabolism; D012243:Rhodopsin / Q000737:chemistry* / Q000378:metabolism
D012243:Rhodopsin; D012172:Retinaldehyde