Signalling States of Photoactivated Rhodopsin

Hofmann, Klaus Peter

doi:10.1002/9780470515693.ch10

Cited by 14 publications

(9 citation statements)

References 65 publications

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“…In rhodopsin, GluIII:04 (Glu 113 ) functions as the counter ion for the LysVII:10 (Lys 256 )-mediated, covalent Schiff-base attachment of retinal. In relation to the ligands of this study, it is notable that the overall structural difference between the highly efficacious inverse agonist 11-cis-retinal and the all-trans agonist form of retinal in fact is not very big (21,22). Importantly, however, during light activation, which turns the inverse agonist 11-cis into the all-trans agonist, the Schiff-base attachment of the ligand is broken (23).…”

Section: Molecular Efficacy Switch In the Ghrelinmentioning

confidence: 86%

Identification of an Efficacy Switch Region in the Ghrelin Receptor Responsible for Interchange between Agonism and Inverse Agonism

Holst

Mokrosiński

Lang

et al. 2007

Journal of Biological Chemistry

106

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The carboxyamidated wFwLL peptide was used as a core ligand to probe the structural basis for agonism versus inverse agonism in the constitutively active ghrelin receptor. In the ligand, an efficacy switch could be built at the N terminus, as exemplified by AwFwLL, which functioned as a high potency agonist, whereas KwFwLL was an equally high potency inverse agonist. The wFw-containing peptides, agonists as well as inverse agonists, were affected by receptor mutations covering the whole main ligand-binding pocket with key interaction sites being an aromatic cluster in transmembrane (TM)-VI and -VII and residues on the opposing face of TM-III. Gain-of-function in respect of either increased agonist or inverse agonist potency or swap between high potency versions of these properties was obtained by substitutions at a number of positions covering a broad area of the binding pocket on TM-III, -IV, and -V. However, in particular, space-generating substitutions at position III:04 shifted the efficacy of the ligands from inverse agonism toward agonism, whereas similar substitutions at position III: 08, one helical turn below, shifted the efficacy from agonism toward inverse agonism. It is suggested that the relative position of the ligand in the binding pocket between this "efficacy shift region" on TM-III and the opposing aromatic cluster on TM-VI and TM-VII leads either to agonism, i.e. in a superficial binding mode, or it leads to inverse agonism, i.e. in a more profound binding mode. This relationship between different binding modes and opposite efficacy is in accordance with the Global Toggle Switch model for 7TM receptor activation. 7TM3 receptors (G-protein-coupled receptors) constitute one of the largest superfamilies of proteins, which also serve as targets for a large proportion of current medical drugs. In particular members of the family A or rhodopsin-like 7TM receptors, which also is the largest family, are considered to be rather easy drug targets. Most of these receptors are antagonist-prone, i.e. if they are screened with libraries of small organic, drug-like molecules, most if not all of the hits will be antagonists, inhibiting agonist-induced signal transduction, when they are tested in functional assays (1). However, a small proportion of the 7TM receptors, including, for example, the complement C5a receptor, the melanocortin MC4 receptor, and the ghrelin receptor, are instead agonist-prone, i.e. most of the screening hits are agonists in functional assays (2). Part of the reason for this is probably that these receptors are characterized by a rather high degree of constitutive, ligand-independent signaling activity, i.e. in the conformational equilibrium these receptors are at least partly biased for active conformation(s) (1). The ghrelin receptor (Fig. 1), for example, is among the most constitutively active receptors as it signals with ϳ50%, depending on the signal transduction pathway, of its maximal signaling capacity without the presence of any hormone (3, 4). High constitutive activity has b...

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Section: Molecular Efficacy Switch In the Ghrelinmentioning

confidence: 86%

Identification of an Efficacy Switch Region in the Ghrelin Receptor Responsible for Interchange between Agonism and Inverse Agonism

Holst

Mokrosiński

Lang

et al. 2007

Journal of Biological Chemistry

106

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“…by protonation, facilitates formation of the active receptor conformation [91,92,135]. In rhodopsin, the energy which is provided by photon absorption and used for retinal cis/trans isomerization shifts the pK a for proton uptake and formation of the Meta II conformation to higher values compared with formation of the opsin* conformation [136,137].…”

Section: Alterations In the Retinal Binding Sitementioning

confidence: 99%

Crystal structure of the ligand-free G-protein-coupled receptor opsin

Park

Scheerer

Hofmann

et al. 2008

Nature

Self Cite

853

925

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Compared with the known structure of inactive rhodopsin, opsin displays prominent structural changes in the conserved E(D)RY and NPxxY(x) 5,6 F regions and TM5-TM7. At the cytoplasmic side, TM6 is tilted outwards by 6-7 Å, whereas the helix structure of TM5 is more elongated and close to TM6. These structural changes, of which some are attributed to an active GPCR state, reorganize the empty retinal binding pocket to disclose two openings for exit and entry of retinal. The opsin structure thus sheds new light on binding of hydrophobic ligands to GPCRs, GPCR activation and signal transfer to the G protein.

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“…The first active-state GPCR structure was that of opsin, the retinal-free form of rhodopsin [16]. Upon light activation, retinal isomerizes and initiates a series of conformational changes leading to the formation of metarhodopsin II, the conformational state capable of activating the G protein tranducin [17]. Following the formation of metarhodopsin II, the Schiff base is hydrolyzed and retinal dissociates to generate opsin (the retinal-free form of rhodopsin).…”

Section: Active-state Gpcr Structuresmentioning

confidence: 99%

Nanobody stabilization of G protein-coupled receptor conformational states

Steyaert

Kobilka

2011

Current Opinion in Structural Biology

211

194

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Remarkable progress has been made in the field of G protein coupled receptor (GPCR) structural biology during the past four years. Several obstacles to generating diffraction quality crystals of GPCRs have been overcome by combining innovative methods ranging from protein engineering to lipid-based screens and microdiffraction technology. The initial GPCR structures represent energetically stable inactive-state conformations. However, GPCRs signal through different G protein isoforms or G protein-independent effectors upon ligand binding suggesting the existence of multiple ligand-specific active states. These active-state conformations are unstable in the absence of specific cytosolic signaling partners representing new challenges for structural biology. Camelid single chain antibody fragments (nanobodies) show promise for stabilizing active GPCR conformations and as chaperones for crystallogenesis.

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Signalling States of Photoactivated Rhodopsin

Cited by 14 publications

References 65 publications

Identification of an Efficacy Switch Region in the Ghrelin Receptor Responsible for Interchange between Agonism and Inverse Agonism

Identification of an Efficacy Switch Region in the Ghrelin Receptor Responsible for Interchange between Agonism and Inverse Agonism

Crystal structure of the ligand-free G-protein-coupled receptor opsin

Nanobody stabilization of G protein-coupled receptor conformational states

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