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Role of the conserved NPxxY(x)5,6F motif in the rhodopsin ground state and during activation.

ABSTRACT: In the G protein-coupled receptor rhodopsin, the conserved NPxxY(x)(5,6)F motif connects the transmembrane helix VII and the cytoplasmic helix 8. The less geometrically constrained retinal analogue 9-demethyl-retinal prevents efficient transformation of rhodopsin to signaling metarhodopsin (Meta) II after retinal photoisomerization. Here, we demonstrate that Ala replacement mutations within the NPxxY(x)(5,6)F domain, which eliminate an interaction between aromatic residues Y306 and F313, allow formation of Meta II despite the presence of 9-demethyl-retinal. Also a disulfide bond linking residues 306 and 313 in the 9-demethyl-retinal-reconstituted mutant Y306C/F313C/C316S prevented Meta II formation, whereas the reduced form of the mutant readily transformed to Meta II after illumination. These observations suggest that the interaction between residues 306 and 313 is disrupted during the Meta I/Meta II transition. However, this enhancement in Meta II formation is not reflected in the G protein activation, which is dramatically reduced for these mutants, suggesting that changes in the Y306-F313 interaction also lead to a proper realigning of helix 8 after photoisomerization. The E134Q mutation, located in the second conserved motif, D(E)RY, rescues activity in 9-demethyl-retinal-reconstituted mutants to different degrees, depending on the position of the Ala replacement in the NPxxY(x)(5,6)F motif, thus revealing distinct roles for the NP and Y(x)(5,6)F portions. Our studies underscore the importance of the NPxxY(x)(5,6)F and D(E)RY motifs in providing structural constraints in rhodopsin that rearrange in response to photoisomerization during formation of the G protein-activating Meta II. The dual control of the structural rearrangements secures reliable transformation of quiescent rhodopsin to activating Meta II.

SUBMITTER: Fritze O

PROVIDER: S-EPMC151333 | biostudies-literature | 2003 Mar

REPOSITORIES: biostudies-literature

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Role of the conserved NPxxY(x)5,6F motif in the rhodopsin ground state and during activation.

Fritze Olaf O Filipek Sławomir S Kuksa Vladimir V Palczewski Krzysztof K Hofmann Klaus Peter KP Ernst Oliver P OP

Proceedings of the National Academy of Sciences of the United States of America 20030224 5

In the G protein-coupled receptor rhodopsin, the conserved NPxxY(x)(5,6)F motif connects the transmembrane helix VII and the cytoplasmic helix 8. The less geometrically constrained retinal analogue 9-demethyl-retinal prevents efficient transformation of rhodopsin to signaling metarhodopsin (Meta) II after retinal photoisomerization. Here, we demonstrate that Ala replacement mutations within the NPxxY(x)(5,6)F domain, which eliminate an interaction between aromatic residues Y306 and F313, allow f ...[more]

PMID: 12601165

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Project description:Rhodopsin is a canonical member of class A of the G protein-coupled receptors (GPCRs) that are implicated in many of the drug interventions in humans and are of great pharmaceutical interest. The molecular mechanism of rhodopsin activation remains unknown as atomistic structural information for the active metarhodopsin II state is currently lacking. Solid-state (2)H NMR constitutes a powerful approach to study atomic-level dynamics of membrane proteins. In the present application, we describe how information is obtained about interactions of the retinal cofactor with rhodopsin that change with light activation of the photoreceptor. The retinal methyl groups play an important role in rhodopsin function by directing conformational changes upon transition into the active state. Site-specific (2)H labels have been introduced into the methyl groups of retinal and solid-state (2)H NMR methods applied to obtain order parameters and correlation times that quantify the mobility of the cofactor in the inactive dark state, as well as the cryotrapped metarhodopsin I and metarhodopsin II states. Analysis of the angular-dependent (2)H NMR line shapes for selectively deuterated methyl groups of rhodopsin in aligned membranes enables determination of the average ligand conformation within the binding pocket. The relaxation data suggest that the beta-ionone ring is not expelled from its hydrophobic pocket in the transition from the pre-activated metarhodopsin I to the active metarhodopsin II state. Rather, the major structural changes of the retinal cofactor occur already at the metarhodopsin I state in the activation process. The metarhodopsin I to metarhodopsin II transition involves mainly conformational changes of the protein within the membrane lipid bilayer rather than the ligand. The dynamics of the retinylidene methyl groups upon isomerization are explained by an activation mechanism involving cooperative rearrangements of extracellular loop E2 together with transmembrane helices H5 and H6. These activating movements are triggered by steric clashes of the isomerized all-trans retinal with the beta4 strand of the E2 loop and the side chains of Glu(122) and Trp(265) within the binding pocket. The solid-state (2)H NMR data are discussed with regard to the pathway of the energy flow in the receptor activation mechanism.

Dataset Information

Role of the conserved NPxxY(x)5,6F motif in the rhodopsin ground state and during activation.

Publications

Role of the conserved NPxxY(x)5,6F motif in the rhodopsin ground state and during activation.

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