Active States of Rhodopsin

Ernst, Oliver P.; Bartl, Franz

doi:10.1002/1439-7633(20021004)3:10<968::aid-cbic968>3.0.co;2-q

Cited by 31 publications

(33 citation statements)

References 57 publications

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“…1 (11)]. These findings suggested a two-step activation scheme, in which the loss of the proton from the retinal SB and the uptake of a proton to the ERY region marked two consecutive transitions (12)(13)(14)(15). Early products with a deprotonated Schiff base (16) and MI-like products that interact with the G protein but do not release GDP from the G protein nucleotide-binding site (17) have been described.…”

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confidence: 98%

Sequence of late molecular events in the activation of rhodopsin

Knierim

Hofmann

Ernst

et al. 2007

Proc. Natl. Acad. Sci. U.S.A.

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Activation of the G protein-coupled receptor rhodopsin involves both the motion of transmembrane helix 6 (TM6) and proton exchange events. To study how these activation steps relate to each other, spin-labeled rhodopsin in solutions of dodecyl maltoside was used so that time-resolved TM6 motion and proton exchange could each be monitored as a function of pH and temperature after an activating light flash. The results reveal that the motion of TM6 is not synchronized with deprotonation of the Schiff base that binds the chromophore to the protein but is an order of magnitude slower at 30°C. However, TM6 motion and the uptake of a proton from solution in the neutral pH range follow the same time course. Importantly, the motion of TM6 is virtually independent of pH, as is Schiff base deprotonation under the conditions used, whereas proton uptake titrates with a pK of 6.5. This finding shows that proton uptake is a consequence rather than a cause of helix motion. Activated rhodopsin binds to and subsequently activates the cognate G protein, transducin. It has been shown that peptides derived from the C terminus of the transducin ␣-subunit mimic in part binding of the intact G protein. These peptides are found to bind to rhodopsin after TM6 movement, resulting in the release of protons. Collectively, the data suggest the following temporal sequence of events involved in activation: (i) internal Schiff base proton transfer; (ii) TM6 movement; and (iii) proton uptake from solution and binding of transducin.G protein-coupled receptor ͉ membrane proteins ͉ spin labeling ͉ retinal protein ͉ photorecptor G protein-coupled receptors (GPCRs) are seven transmembrane helix (TM) proteins. After receiving a chemical or physical stimulus such as ligand binding or photon absorption, they are activated and catalyze nucleotide exchange in heterotrimeric G proteins (G␣␤␥) (1, 2). Rhodopsin is the prototype and eponym of the largest class of GPCRs, the rhodopsin-like receptors (class A). Rhodopsin consists of the apoprotein opsin and the covalently bound chromophore 11-cis-retinal, which is connected to the protein through a protonated Schiff base to Lys-296 (SB; Fig. 1 Inset). Absorption of a photon by dark rhodopsin (ground state) leads to fast isomerization of the 11-cis-retinal to the all-trans configuration. After several shortlived photointermediates (photo-, batho-, lumirhodopsin), rhodopsin finally arrives at a pH-and temperature-dependent equilibrium between the two states metarhodopsin I (MI) and metarhodopsin II (MII) (3). In the MI state, the retinal SB is still protonated. Deprotonation of the SB by internal proton transfer occurs during transition to MII and can be tracked by the blue shift of the UV/visible absorption maximum ( max,rhodopsin ϭ 500 nm to max,MII ϭ 380 nm). Importantly, MII formation is linked to the uptake of a proton from the aqueous phase (4-6).A paradigm of rhodopsin activation arose from photointermediate measurements. It was recognized that the interaction of rhodopsin with its G protein transducin (...

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confidence: 98%

Sequence of late molecular events in the activation of rhodopsin

Knierim

Hofmann

Ernst

et al. 2007

Proc. Natl. Acad. Sci. U.S.A.

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“…The majority of signals are chemical ligands, such as hormones or pheromones, which reach their GPCR by diffusion and bind to a site near their extracellular surface (1,2). Photoreceptors contain a chromophore as a fixed prostethic group and are specialized for the detection of quanta of visible light in the environment (3,4).…”

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confidence: 99%

Transition of Rhodopsin into the Active Metarhodopsin II State Opens a New Light-induced Pathway Linked to Schiff Base Isomerization

Ritter

Zimmermann

Heck

et al. 2004

Journal of Biological Chemistry

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Rhodopsin bears 11-cis-retinal covalently bound by a protonated Schiff base linkage. 11-cis/all-trans isomerization, induced by absorption of green light, leads to active metarhodopsin II, in which the Schiff base is intact but deprotonated. The subsequent metabolic retinoid cycle starts with Schiff base hydrolysis and release of photolyzed all-trans-retinal from the active site and ends with the uptake of fresh 11-cis-retinal. To probe chromophore-protein interaction in the active state, we have studied the effects of blue light absorption on metarhodopsin II using infrared and time-resolved UVvisible spectroscopy. A light-induced shortcut of the retinoid cycle, as it occurs in other retinal proteins, is not observed. The predominantly formed illumination product contains all-trans-retinal, although the spectra reflect Schiff base reprotonation and protein deactivation. By its kinetics of formation and decay, its low temperature photointermediates, and its interaction with transducin, this illumination product is identified as metarhodopsin III. This species is known to bind alltrans-retinal via a reprotonated Schiff base and forms normally in parallel to retinal release. We find that its generation by light absorption is only achieved when starting from active metarhodopsin II and is not found with any of its precursors, including metarhodopsin I. Based on the finding of others that metarhodopsin III binds retinal in all-trans-C 15 -syn configuration, we can now conclude that light-induced formation of metarhodopsin III operates by Schiff base isomerization ("second switch"). Our reaction model assumes steric hindrance of the retinal polyene chain in the active conformation, thus preventing central double bond isomerization.Living cells react to stimuli, which are realized in physical or chemical signals and are often detected by specialized membrane receptor proteins. G-protein-coupled receptors (GPCRs) 1 transmit their signal to heterotrimeric G-proteins via cytoplasmic domains of their seven-transmembrane ␣-helical structure. The majority of signals are chemical ligands, such as hormones or pheromones, which reach their GPCR by diffusion and bind to a site near their extracellular surface (1, 2). Photoreceptors contain a chromophore as a fixed prostethic group and are specialized for the detection of quanta of visible light in the environment (3, 4). The first step in the signal transduction pathway mediated by these receptors is the generation of a short-lived electronically excited state caused by photon absorption to channel the energy into a conformationally and/or chemically altered state of chromophore-protein interaction (5). Although these early events of light absorption are lacking in ligand binding receptors, G-protein-coupled photoreceptors may use similar mechanisms to spread the local activation near the ligand binding site to the cytoplasmic binding sites, where the G-protein has access. In this view, the chromophore can be understood as a fixed ligand that becomes an agonist by light absorpt...

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“…However, comparing the UR with the PR molecules, important differences are observed in carbons 7,9,11,12,13 and the N atom. In all of the bonds, the −90°conformer shows a peak.…”

Section: Interatomic Distances and Atomic Bond Ordermentioning

confidence: 99%

“…In prokaryote type 1 opsins, however, e.g., bacteriorhodopsin (Br), the photoisomerization of retinal occurs from alltrans to 13-cis configurations, and the obtained photoenergy is used for proton or ion pumping outside the cell membrane. 12 Meta II can decay or be converted after several minutes to meta III, which can be reprotonated, starting the photocycle of rhodopsin. 5 The cis to trans retinal reaction has been analyzed extensively in computational and experimental studies.…”

Section: Introductionmentioning

confidence: 99%

“…4 The biophysics of vision starts with light energy activation of the chromophore cis retinal, which is covalently bonded to the opsin (apoprotein) through the N atom of the side-chain of Lys296, as found in the bovine eye (Bos taurus), which forms a positively charged Schiff's base (SB). 12,13 Interestingly, in the UV vision that is found in many species of birds, reptiles, fishes, and rodents, retinal is in the unprotonated condition. [6][7][8][9][10] Thus, by ultrafast optical spectroscopic methodology, the photoisomerization reaction has been accurately unveiled, which confirms that between the potential energy surfaces of the ground and excited states, there occurs a conical intersection, which a Instituto de Investigaciones Biomédicas, Universidad Nacional Autónoma de México, México, D.F.…”

Section: Introductionmentioning

confidence: 99%

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Atomic and molecular analysis highlights the biophysics of unprotonated and protonated retinal in UV and scotopic vision

Kubli‐Garfias

Vázquez‐Ramírez

Cabrera‐Vivas

et al. 2015

Photochem Photobiol Sci

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During the photoreaction of rhodopsin, retinal isomerizes, rotating the C11[double bond, length as m-dash]C12 π-bond from cis to an all-trans configuration. Unprotonated (UR) or protonated (PR) retinal in the Schiff's base (SB) is related to UV and light vision. Because the UR and PR have important differences in their physicochemical reactivities, we compared the atomic and molecular properties of these molecules using DFT calculations. The C10-C11[double bond, length as m-dash]C12-C13 dihedral angle was rotated from 0° to 180° in 45° steps, giving five conformers, and the following were calculated from them: atomic orbital (AO) contributions to the HOMO and LUMO, atomic charges, bond length, bond order, HOMO, LUMO, hardness, electronegativity, polarizability, electrostatic potential, UV-vis spectra and dipole moment (DM). Similarly, the following were analyzed: the energy profile, hybridization, pyramidalization and the hydrogen-out-of-plane (HOOP) wagging from the H11-C11[double bond, length as m-dash]C12-H12 dihedral angle. In addition, retinal with a water H-bond (HR) in the SB was included for comparison. Interestingly, in the PR, C11 and C12 are totally the LUMO and the HOMO, respectively, and have a large electronegativity difference, which predicts an electron jump in these atoms during photoexcitation. At the same time, the PR showed a longer bond length and lower bond order, with a larger DM, lower HOMO-LUMO gap, lower hardness and higher electronegativity. In addition, the AOs of -45° and -90° conformers changed significantly, from pz to py, during the rotation concomitantly with marked hybridization, smooth pyramidalization and lower HOOP activity. Clearly, the atomic and molecular differences between the UR and PR are overwhelming, including the rotational energy profile and light absorption spectra, which indicates that light absorption of UR and PR is already determined by the retinal characteristics of the SB protonation. The HR-model compared with UR shows a lower energy barrier and a discreet bathochromic effect in the UV region.

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Active States of Rhodopsin

Cited by 31 publications

References 57 publications

Sequence of late molecular events in the activation of rhodopsin

Sequence of late molecular events in the activation of rhodopsin

Transition of Rhodopsin into the Active Metarhodopsin II State Opens a New Light-induced Pathway Linked to Schiff Base Isomerization

Atomic and molecular analysis highlights the biophysics of unprotonated and protonated retinal in UV and scotopic vision

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