The Molecular Mechanism of Visual Excitation and Its Relation to the Structure and Composition of the Rod Outer Segment

Liebman, Paul A.; Parker, K.R.; Dratz, Edward A.

doi:10.1146/annurev.ph.49.030187.004001

Cited by 257 publications

(82 citation statements)

References 103 publications

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“…Rhodopsin is activated by photon absorption, causing cis-trans isomerization of the chromophore 11-cis-retinal, which is bound covalently to the apoprotein opsin. Optimal photon absorption of photoreceptor cells is ensured by the high density of rhodopsin in the disk membranes [Ͼ25,000 receptors per m 2 (3)]. …”

mentioning

confidence: 99%

Monomeric G protein-coupled receptor rhodopsin in solution activates its G protein transducin at the diffusion limit

Ernst

Gramse

Kolbe

et al. 2007

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

200

163

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G protein-coupled receptors mediate biological signals by stimulating nucleotide exchange in heterotrimeric G proteins (G␣␤␥).Receptor dimers have been proposed as the functional unit responsible for catalytic interaction with G␣␤␥. To investigate whether a G protein-coupled receptor monomer can activate G␣␤␥, we used the retinal photoreceptor rhodopsin and its cognate G protein transducin (G t) to determine the stoichiometry of rhodopsin/Gt binding and the rate of catalyzed nucleotide exchange in G t. Purified rhodopsin was prepared in dodecyl maltoside detergent solution. Rhodopsin was monomeric as concluded from fluorescence resonance energy transfer, copurification studies with fluorescent labeled and unlabeled rhodopsin, size exclusion chromatography, and multiangle laser light scattering. A 1:1 complex between light-activated rhodopsin and G t was found in the elution profiles, and one molecule of GDP was released upon complex formation. Analysis of the speed of catalytic rhodopsin/G t interaction yielded a maximum of Ϸ50 Gt molecules per second and molecule of activated rhodopsin. The bimolecular rate constant is close to the diffusion limit in the diluted system. The results show that the interaction of Gt with an activated rhodopsin monomer is sufficient for fully functional Gt activation. Although the activation rate in solution is at the physically possible limit, the rate in the native membrane is still 10-fold higher. This is likely attributable to the precise orientation of the G protein to the membrane surface, which enables a fast docking process preceding the actual activation step. Whether docking in membranes involves the formation of rhodopsin dimers or oligomers remains to be elucidated. enzyme catalysis ͉ nucleotide exchange ͉ light scattering

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mentioning

confidence: 99%

Monomeric G protein-coupled receptor rhodopsin in solution activates its G protein transducin at the diffusion limit

Ernst

Gramse

Kolbe

et al. 2007

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

200

163

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“…More direct evidence comes from the work of Levitzki and his colleagues who have consistently argued from both kinetic analyses (Tolkovsky & Levitzki, 1978a;Levitzki, 1986) and the physical association of G. and adenylate cyclase during substantial purification (Arad et al, 1984) that G., at least, remains tightly bound to its effector, and therefore to the membrane, throughout the G protein cycle. Even transducin, the G protein that is least tightly associated with the membrane, may not significantly dissociate from the disc membrane after activation under physiological conditions (Liebman et al, 1987;Uhl et al, 1990), although Chabre (1987) has argued that the°Ct-GTP subunit is soluble and becomes a cytoplasmic messenger. The adverse consequences of active a subunits leaving the membrane would certainly be less serious in rods than in more typical, less specialized, cells.…”

Section: G Protein Activationmentioning

confidence: 99%

“…The speed of the process is limited only by the very rapid rates of intramolecular movements of proteins, and these allow the nicotinic receptor to begin to respond within 20 ,us of addition of acetylcholine (Katz & Miledi, 1965). For receptor tyrosine kinases activation is a much slower process because, at least for the EGF receptor, stimulation of the kinase activity requires an interaction between two receptors with EGF bound (Yarden & Schlessinger, 1987 (Liebman et al, 1987). However, receptors and G proteins interact at the surface of a membrane and not free in solution.…”

Section: Sensitivity Of Receptorsmentioning

confidence: 99%

“…However, receptors and G proteins interact at the surface of a membrane and not free in solution. The result is to both effectively 'concentrate' the proteins-they are diluted in two rather than three dimensions, and the proteins can be presented to each other in favourable orientations (Liebman et al, 1987). Both processes will increase the rates of productive interaction between receptors and G proteins.…”

Section: Sensitivity Of Receptorsmentioning

confidence: 99%

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The role of G proteins in transmembrane signalling

Taylor

1990

Biochemical Journal

226

113

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INTRODUCTIONIn some transmembrane signalling systems detection of the extracellular stimulus and generation of an intracellular response are properties of the same protein or protein complex. Binding of acetylcholine to the a subunits of the pentameric nicotinic receptor, for example, opens a cation-selective channel formed by parts of each of the receptor subunits, and insulin when it binds to the extracellular domain of its receptor activates a protein tyrosine kinase activity in the intracellular domain of the same protein. Rodbell and his collaborators (Rodbell et al., 1971) were the first to provide evidence for a more complex class of signalling pathway where the sensor and intracellular effector are separate proteins that communicate through a guanine nucleotide-dependent regulatory protein or G protein. The G protein cycles between inactive GDP-bound and active GTPbound forms. Activation is catalysed by receptors and deactivation is an intrinsic property of the G protein, its GTPase activity. The developments that followed Rodbell's pioneering studies have established that many different receptors regulate many intracellular effectors through a family of closely related G proteins (Citri & Schramm, 1980;Rodbell, 1980;Schramm & Selinger, 1984;Northup, 1985;Levitzki, 1988). Many excellent recent reviews have focused on various aspects of these interactions between receptors, G proteins and intracellular effectors (Casperson & Bourne, 1987;Gilman, 1987;Allende, 1988;Lochrie & Simon, 1988;Weiss et al., 1988;Chabre & Deterre, 1989;Ross, 1989;Houslay, 1990).The G protein cycle, at the centre of the conversation between receptors and their effectors, provides one solution to the compromise that cells must make between responding rapidly and being able to respond to very low concentrations of extracellular stimulus. In this review I will consider how different signalling mechanisms are adapted to the cellular processes they control by comparing the properties of the signalling pathways that involve G proteins with the simpler pathways that do not.

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“…In the photoreceptor cell they mediate communication between photoexcited rhodopsin and a cGMP-specific phosphodiesterase [2,3]. The cGMP concentration, in turn, modulates the conducting properties of the plasma membrane and hence the current entering the photoreceptor [4,5].…”

Section: Introductionmentioning

confidence: 99%

Sub‐second turnover of transducin GTPase in bovine rod outer segments A light scattering study

1988

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A fast, regenerative light scattering signal from bovine ROS, the PA-signal, reflects the light-induced, transient activation of transducin.Its rate of recovery depends on the number of photolysed rhodopsin molecules, indicating that rhodopsin deactivation and not GTPase activity is rate limiting in our in vitro system. When rhodopsin deactivation is accelerated (in the presence of NH,OH), PA-signal recovery is also accelerated. A GTPase turnover number of more than 2 s-l (at 37°C) can bc derived from these experiments. This is more than one order of magnitude faster than the GTPase rates so far described in the literature and is rapid enough for a physiological shut-off mechanism. The fast GTPase is attributed to a highly intact disk stack, which never releases transducin into the free aqueous space.

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The Molecular Mechanism of Visual Excitation and Its Relation to the Structure and Composition of the Rod Outer Segment

Cited by 257 publications

References 103 publications

Monomeric G protein-coupled receptor rhodopsin in solution activates its G protein transducin at the diffusion limit

Monomeric G protein-coupled receptor rhodopsin in solution activates its G protein transducin at the diffusion limit

The role of G proteins in transmembrane signalling

Sub‐second turnover of transducin GTPase in bovine rod outer segments A light scattering study

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