Secondary binding sites of retinoids in opsin: characterization and role in regeneration

Heck, M.; Schädel, Sandra A.; Maretzki, D; Hofmann, Klaus Peter

doi:10.1016/j.visres.2003.08.011

Cited by 42 publications

(51 citation statements)

References 19 publications

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“…Our findings are in agreement and support the results of previous studies proposing that more than one retinoid can interact with visual opsins [ 40 ] which strongly suggests the presence of functionally relevant secondary binding sites of retinoids in opsin [ 41 ]. Furthermore, previous experimental evidence showed an important role for non-covalent 11CR binding to opsin prior to regeneration [ 42 ] and in its ability to bind to a selective conformation of the protein among various conformational modes of visual pigments prior and after photoactivation [ 39 ].…”

Section: Figsupporting

confidence: 92%

Beyond spectral tuning: human cone visual pigments adopt different transient conformations for chromophore regeneration

Srinivasan

Cordomí

Ramon

et al. 2015

Cell. Mol. Life Sci.

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Human red and green visual pigments are seven transmembrane receptors of cone photoreceptor cells of the retina that mediate color vision. These pigments share a very high degree of homology and have been assumed to feature analogous structural and functional properties. We report on a different regeneration mechanism among red and green cone opsins with retinal analogs using UV-Vis/fluorescence spectroscopic analyses, molecular modeling and site-directed mutagenesis. We find that photoactivated green cone opsin adopts a transient conformation which regenerates via an unprotonated Schiff base linkage with its natural chromophore, whereas red cone opsin forms a typical protonated Schiff base. The chromophore regeneration kinetics is consistent with a secondary retinal uptake by the cone pigments. Overall, our findings reveal, for the

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Section: Figsupporting

confidence: 92%

Beyond spectral tuning: human cone visual pigments adopt different transient conformations for chromophore regeneration

Srinivasan

Cordomí

Ramon

et al. 2015

Cell. Mol. Life Sci.

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“…Is it related to the observation that adding detergent to membrane-bound Rho also affects retinal release and uptake, or "ligand channeling"? Some have proposed that a secondary retinal binding site is formed by Helix 8 of Rho (42)(43)(44), and detergent may disrupt the interaction of the palmitoyl anchors of Helix 8 with the membrane. Because we found that arrestin and retinal release were decoupled in detergent, our results may imply a role for ligand channeling in arrestin release.…”

Section: Discussionmentioning

confidence: 99%

Dynamics of Arrestin-Rhodopsin Interactions

Sommer

Smith

Farrens

2006

Journal of Biological Chemistry

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We report that acidic phospholipids can restore the binding of visual arrestin to purified rhodopsin solubilized in n-dodecyl-␤-Dmaltopyranoside. We used this finding to investigate the interplay between arrestin binding and the status of the retinal chromophore ligand in the receptor binding pocket. Our results showed that arrestin can interact with the late photoproduct Meta III and convert it to a Meta II-like species. Interestingly in these mixed micelles, the release of retinal and arrestin was no longer directly coupled as it is in the native rod disk membrane. For example, up to ϳ50% of the retinal could be released even though arrestin remains bound to the receptor in a long lived complex. We anticipate that this new ability to study these proteins in a defined, purified system will facilitate further structural and dynamic studies of arrestinrhodopsin interactions.The integral membrane protein rhodopsin (Rho) 2 enables the conversion of light to nerve signals in the rod cells, resulting in dim light vision (1-3). In the dark, the chromophore (11-cis-retinal) is linked to Rho at Lys 296 by a protonated Schiff base ( max ϳ 500 nm). Light absorption isomerizes the chromophore to all-trans-retinal. Within milliseconds two photoproducts evolve, Meta I ( max ϳ 480 nm) and Meta II ( max ϳ 380 nm), which are in a pH-and temperature-sensitive equilibrium.The ability of Meta II to bind and activate the G-protein transducin (4) is terminated in several ways. Meta II can decay through hydrolysis of the Schiff base linkage and release of retinal, a process that takes ϳ1 min at physiological temperature and pH (5). Alternatively Meta II can decay to the long lived retinal storage photoproduct Meta III ( max ϳ 470 nm) in which the Schiff base is intact and protonated (6 -9). Finally Rho signaling can be blocked through a series of protein-protein interactions that involves phosphorylation of the C-terminal tail of Rho by Rho kinase and binding of the protein arrestin (10).Earlier we found that these inactivation mechanisms are related. That is, arrestin release and retinal release appear to be directly linked events: both are described by similar activation energies, and arrestin slows the rate of retinal release ϳ2-fold at physiological temperatures. Intriguingly we also found that a fraction of the arrestin remains bound to ROS*-P long after "active" Meta II decay (5).In the present work, we expanded upon these studies and made several surprising discoveries. First, we found that adding phospholipids restores arrestin binding to purified Rho*-P solubilized in n-dodecyl-␤-D-maltopyranoside (DM). Second, we clearly established in the mixed micelle system that arrestin interacts with the post-Meta II photodecay product Meta III. Finally we found that arrestin and retinal release appear to be unlinked in mixed micelles with the acidic phospholipids PS, PI, and PA showing a more pronounced effect than the neutral phospholipids PC and PE ( Fig. 1 shows a scheme of the different lipid head groups). Intriguingly with the ...

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“…Experiments were performed at 20°C in 20 mM BisTris propane (pH 6.5) and 0.1% (w/v) ␤-dodecyl maltoside (23). Directly after solubilization of opsin (1 M) in disk membranes with ␤-dodecyl maltoside (0.1% (w/v) final concentration), pigments were regenerated by addition of 0.8 M retinal and analyzed in a total volume of 650 l. For conversion to Meta II, samples were illuminated for 15 s with orange light (Schott GG495 or GG475 long-pass filter) using the same equipment used for UV-visible spectroscopy.…”

Section: Methodsmentioning

confidence: 99%

Partial Agonism in a G Protein-coupled Receptor

Bartl

Fritze

Ritter

et al. 2005

Journal of Biological Chemistry

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The visual process in rod cells is initiated by absorption of a photon in the rhodopsin retinal chromophore and consequent retinal cis/trans-isomerization. The ring structure of retinal is thought to be needed to transmit the photonic energy into conformational changes culminating in the active metarhodopsin II (Meta II) intermediate. Here, we demonstrate that cis-acyclic retinals, lacking four carbon atoms of the ring, can activate rhodopsin. Detailed analysis of the activation pathway showed that, although the photoproduct pathway is more complex, Meta II formed with almost normal kinetics. However, lack of the ring structure resulted in a low amount of Meta II and a fast decay of activity. We conclude that the main role of the ring structure is to maintain the active state, thus specifying a mechanism of activation by a partial agonist of the G protein-coupled receptor rhodopsin.Rhodopsin is the visual pigment of the rod photoreceptor cell and gains its spectral properties from the chromophore 11-cis-retinal, which is covalently linked by a protonated Schiff base to Lys-296 of the apoprotein opsin (see Fig. 1). Rhodopsin is also the only G protein-coupled receptor (GPCR) 4 whose crystal structure is solved (1-3). Insight into its mechanism of activation increases our understanding of how GPCRs work. Rhodopsin activation is triggered by the chromophore capture of a photon, which causes ultra fast cis/trans-isomerization of retinal. The photonic energy is used for conversion of the chromophore from an inverse agonist to a potent agonist and is channeled into protein conformational changes. This enables the cytoplasmic surface of the receptor to catalyze nucleotide exchange in the heterotrimeric G protein transducin (G t ) (4).The retinal-binding pocket is flexible enough to harbor a variety of synthetic retinal analogs, making them convenient probes of rhodopsin function (5). Specific protein-chromophore interactions ensure the low activity of rhodopsin in the dark ground state as well as in the rapid activation process. Removal of parts of the retinal structure is thus useful in identifying important elements of the retinal structure utilized in rhodopsin function. In a previous study, we investigated a retinal analog lacking the methyl group at C-9, termed 11-cis-9-demethylretinal (9-dm-retinal) (see Fig. 1C). 9-dm-retinal exerts its effect on the late metarhodopsin (Meta) photoproducts, Meta I and Meta II, by acting as a partial agonist (6, 7). Meta I is inactive and in equilibrium with the G protein-activating Meta II, thus corresponding to low and high affinity states of GPCRs (4). Recent evidence has further specified the nature of the protein-chromophore interaction in active Meta II. It was shown that, in Meta II and not in earlier intermediates, the central part of the polyene chain is firmly locked in the all-trans-configuration and resists re-isomerization to the ground state (8). Absorption of light in this state does not reverse the activation pathway back to the ground state, as observed for the...

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Secondary binding sites of retinoids in opsin: characterization and role in regeneration

Cited by 42 publications

References 19 publications

Beyond spectral tuning: human cone visual pigments adopt different transient conformations for chromophore regeneration

Beyond spectral tuning: human cone visual pigments adopt different transient conformations for chromophore regeneration

Dynamics of Arrestin-Rhodopsin Interactions

Partial Agonism in a G Protein-coupled Receptor

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