Journal
JOURNAL OF MOLECULAR BIOLOGY
Volume 357, Issue 1, Pages 163-172Publisher
ACADEMIC PRESS LTD- ELSEVIER SCIENCE LTD
DOI: 10.1016/j.jmb.2005.12.046
Keywords
G protein-coupled receptor; solid-state NMR; magic angle spinning; retinal chromophore; rotamer toggle switch
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Funding
- NCRR NIH HHS [S10 RR13889] Funding Source: Medline
- NIGMS NIH HHS [R01 GM041412-14, GM-41412] Funding Source: Medline
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Isomerization of the II-cis retinal chromophore in the visual pigment rhodopsin is coupled to motion of transmembrane helix H6 and receptor activation. We present solid-state magic angle spinning NMR measurements of rhodopsin and the metarhodopsin II intermediate that support the proposal that interaction of Trp265(6.48) with the retinal chromophore is responsible for stabilizing an inactive conformation in the dark, and that motion of the beta-ionone ring allows Trp2656.48 and transmembrane helix H6 to adopt active conformations in the light. Two-dimensional dipolar-assisted rotational resonance NMR measurements are made between the C19 and C20-methyl groups of the retinal and uniformly C-13-labeled Trp265(6.48). The retinal C20-Trp265(6.48) contact present in the dark-state of rhodopsin is lost in metarhodopsin II, and a new contact is formed with the C19 methyl group. We have previously shown that the retinal translates 4-5 angstrom toward H5 in metarhodopsin II. This motion, in conjunction with the Trp-C19 contact, implies that the Trp265(6.48) side-chain moves significantly upon rhodopsin activation. NMR measurements also show that a packing interaction in rhodopsin between Trp265(6.48) and Gly121(3.36) is lost in metarhodopsin II, consistent with H6 motion away from H3. However, a close contact between Gly120(3.35) on H3 and Met86(2.53) on H2 is observed in both rhodopsin and metarhodopsin II, suggesting that H3 does not change orientation significantly upon receptor activation. (c) 2005 Elsevier Ltd. All rights reserved.
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