The Involvement of Water at the Retinal Binding Site in Rhodopsin and Early Light‐induced Intramolecular Proton Transfer

Rafferty, Charles N.; Shichi, Hitoshi

doi:10.1111/j.1751-1097.1981.tb05329.x

Cited by 69 publications

(37 citation statements)

References 23 publications

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“…It has been observed that removal of water molecules from the Schiff base pocket can result in displacement of positive charge away from the Schiff base nitrogen, leading to deprotonation of the Schiff base (Rafferty and Shichi, 1981;Deng et al, 1994;Harosi and Sandorfy, 1995;Nagata et al, 1997). Thus, some (or all) of the eight critical amino acids in the UV pigments may eliminate water molecules in the Schiff base pocket.…”

Section: Discussionmentioning

confidence: 99%

Molecular evolution of color vision in vertebrates

Yokoyama

2002

Gene

261

231

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Visual systems of vertebrates exhibit a striking level of diversity, reflecting their adaptive responses to various color environments. The photosensitive molecules, visual pigments, can be synthesized in vitro and their absorption spectra can be determined. Comparing the amino acid sequences and absorption spectra of various visual pigments, we can identify amino acid changes that have modified the absorption spectra of visual pigments. These hypotheses can then be tested using the in vitro assay. This approach has been a powerful tool in elucidating not only the molecular bases of color vision, but the processes of adaptive evolution at the molecular level. q

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Section: Discussionmentioning

confidence: 99%

Molecular evolution of color vision in vertebrates

Yokoyama

2002

Gene

261

231

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“…Increased intramembranous accessibility to external small molecules and water is required for Rho activation to advance beyond the Meta I state (26,27). Moreover, the retinylidene chromophore becomes accessible to reagents such as NH 2 OH or NaBH 4 only upon attainment of the Meta II state (11,28).…”

Section: Discussionmentioning

confidence: 99%

Role of Bulk Water in Hydrolysis of the Rhodopsin Chromophore

Jastrzębska

Palczewski

Golczak

2011

Journal of Biological Chemistry

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Rhodopsin (Rho) is a prototypical G protein-coupled receptor that changes from an inactive conformational state to a G protein-activating state as a consequence of its retinal chromophore isomerization, 11-cis-retinal 3 all-trans-retinal. The photoisomerized chromophore covalently linked to Lys 296 by a Schiff base is subsequently hydrolyzed, but little is known about this reaction. Recent research indicates a significant role for tightly bound transmembrane water molecules in the Rho activation process. Atomic structures of Rho and hydroxyl radical footprinting reveal ordered waters within Rho transmembrane helices that are located close to highly conserved and functionally important receptor residues, forming a hydrogen bond network. Using 18 O-labeled H 2 O, we now report that water from bulk solvent, but not tightly bound water, is involved in the hydrolytic release of chromophore upon Rho activation by light. Moreover, small molecules (and presumably, water) enter the Rho structure from the cytoplasmic side of the membrane. Thus, this work indicates two distinct origins of water vital for Rho function.Rhodopsin (Rho), 3 the visual pigment in retinal rod photoreceptors, is a G protein-coupled receptor responsible for dim light vision (1, 2). Rho is composed of its apoprotein, opsin, and a retinylidene chromophore in an 11-cis-conformation covalently linked by a Schiff base to Lys 296 of the opsin (Fig. 1A). Photoactivation of Rho is initiated by isomerization of the retinylidene ligand to its all-trans-configuration (3), allowing the photoreceptor after deprotonation of the Schiff base to adopt the active Meta II state required for G protein (transducin) activation. The atomic structure of Rho led to the identification of crystallographically ordered water molecules adjacent to functionally important conserved protein residues (Fig. 1A) (4), supporting the conclusion that these waters are essential not just for structural stabilization of the receptor but also for the activation process. One of these tightly bound waters positioned close to the chromophore-binding pocket has been postulated to play a key role in the counterion switch between ground state (dark; Glu 113 ) and activated states (Glu 181 ) of Rho (5, 6). Moreover, Glu 113 and Glu 181 are also likely involved in the hydrolytic process via the carbinol ammonium ion and in a regeneration reaction between 11-cis-retinal and opsin. To form the Schiff base, Lys 296 must be deprotonated, the carbonyl group must be polarized, and water must be accommodated within the chromophore-binding site (1). Hydroxyl radical footprinting revealed local conformational changes in the Rho structure following its photoactivation, presumably mediated by the dynamics of both ordered water molecules and the protein (7,8). Moreover, protein footprinting combined with rapid H 2 18 O mixing methodology and deuterium-hydrogen exchange on C 2 His residues indicated that these tightly bound internal waters do not exchange with bulk solvent in ground state Rho, Meta II, or opsin...

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“…Structural water forming hydrogen bonds from the PSB to O 2 of Glu-113 (not shown in Fig. 3) is likely to be present (7,42).…”

Section: Scheme IIImentioning

confidence: 99%

“…The distance of the Glu-113 oxygen closest to C12 (referred to as O1) was kept at 3 Å in rho and in batho (7,41). It is likely that structural water forms a hydrogen bond network from O2 of Glu-113 to the SB proton (white) (not shown in this figure) (7,42). In rho, the distances of the SB proton to O2 of Glu-113 in the dark state, batho, bsi, and lumi are 4.6, 4.4, 3.6, and 3.9 Å, respectively.…”

Section: Scheme IIImentioning

confidence: 99%

Chromophore structural changes in rhodopsin from nanoseconds to microseconds following pigment photolysis

Jäger

Lewis

Zvyaga

et al. 1997

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

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Rhodopsin is a prototypical G proteincoupled receptor that is activated by photoisomerization of its 11-cis-retinal chromophore. Mutant forms of rhodopsin were prepared in which the carboxylic acid counterion was moved relative to the positively charged chromophore Schiff base. Nanosecond time-resolved laser photolysis measurements of wild-type recombinant rhodopsin and two mutant pigments then were used to determine reaction schemes and spectra of their early photolysis intermediates. These results, together with linear dichroism data, yielded detailed structural information concerning chromophore movements during the first microsecond after photolysis. These chromophore structural changes provide a basis for understanding the relative movement of rhodopsin's transmembrane helices 3 and 6 required for activation of rhodopsin. Thus, early structural changes following isomerization of retinal are linked to the activation of this G protein-coupled receptor. Such rapid structural changes lie at the heart of the pharmacologically important signal transduction mechanisms in a large variety of receptors, which use extrinsic activators, but are impossible to study in receptors using diffusible agonist ligands.Rhodopsin is the light-triggered membrane receptor in rod outer segments responsible for dim-light vision. Absorption of light transforms rhodopsin (rho) into an activated state, which interacts with a heterotrimeric G protein to initiate an enzyme cascade leading to visual transduction. To reach this active state, called metarhodopsin (meta) II (1, 2), rho passes through a number of intermediates that have been characterized by UV-visible, Fourier-transform infrared (FTIR), Raman, and NMR spectroscopies, in addition to spin-labeling and biochemical studies (3-10). One way to characterize the intermediates is to trap them at low temperatures. This approach led to the classical ''bleaching'' scheme ( max values in nanometers): rho (498) 3 bathorhodopsin (batho) (542) 3 lumirhodopsin (lumi) (497) 3 meta I (480) 3 meta II (380) Scheme I However, at more physiologically relevant temperatures, time-resolved measurements up to 1 msec after photolysis reveal a new intermediate and a different kinetic scheme (3, 11). The following reaction scheme was proposed to occur during the nanosecond-to-microsecond time regime (3): rho (498) 3 batho (529) ª bsi (477) 3 lumi (492) 3 . . . Scheme II The new intermediate, blue-shifted intermediate of rho (bsi), is entropically favored and thus not trapped at low temperatures (11).The role of various structural features of the retinal chromophore in early rho photointermediates has been studied through time-resolved spectral measurements of artificial rho, in which the native chromophore is replaced by synthetically modified retinals (12). In studies of bacteriorhodopsin, timeresolved absorption spectroscopy has been shown to be particularly valuable when combined with site-directed mutagenesis to probe the roles of specific protein residues in different intermediates (13). Unti...

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The Involvement of Water at the Retinal Binding Site in Rhodopsin and Early Light‐induced Intramolecular Proton Transfer

Cited by 69 publications

References 23 publications

Molecular evolution of color vision in vertebrates

Molecular evolution of color vision in vertebrates

Role of Bulk Water in Hydrolysis of the Rhodopsin Chromophore

Chromophore structural changes in rhodopsin from nanoseconds to microseconds following pigment photolysis

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