G proteins and phototransduction.
01 Jan 2002-Annual Review of Physiology (Annual Reviews 4139 El Camino Way, P.O. Box 10139, Palo Alto, CA 94303-0139, USA)-Vol. 64, Iss: 1, pp 153-187
TL;DR: How the interplay between the mechanisms that contribute to amplification and those that govern termination of G protein activity determine the speed and the sensitivity of the cellular response to light is examined.
Abstract: Phototransduction is the process by which a photon of light captured by a molecule of visual pigment generates an electrical response in a photoreceptor cell. Vertebrate rod phototransduction is one of the best-studied G protein signaling pathways. In this pathway the photoreceptor-specific G protein, transducin, mediates between the visual pigment, rhodopsin, and the effector enzyme, cGMP phosphodiesterase. This review focuses on two quantitative features of G protein signaling in phototransduction: signal amplification and response timing. We examine how the interplay between the mechanisms that contribute to amplification and those that govern termination of G protein activity determine the speed and the sensitivity of the cellular response to light.
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TL;DR: In this review, some of the functions of heterotrimeric G proteins in defined cells and tissues are described.
Abstract: Heterotrimeric G proteins are key players in transmembrane signaling by coupling a huge variety of receptors to channel proteins, enzymes, and other effector molecules. Multiple subforms of G proteins together with receptors, effectors, and various regulatory proteins represent the components of a highly versatile signal transduction system. G protein-mediated signaling is employed by virtually all cells in the mammalian organism and is centrally involved in diverse physiological functions such as perception of sensory information, modulation of synaptic transmission, hormone release and actions, regulation of cell contraction and migration, or cell growth and differentiation. In this review, some of the functions of heterotrimeric G proteins in defined cells and tissues are described.
1,074 citations
Cites background from "G proteins and phototransduction."
...Activation of PDE lowers cytosolic cGMP levels leading to a decreased open probability of cGMP-regulated cation channels in the plasma membrane, which eventually results in hyperpolarization of the photoreceptor cells (24)....
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...At least three proteins contribute to the rapid deactivation of transducin by increasing its GTPase activity: RGS9 and G 5L, which form a complex, and the -subunit of the transducin effector cGMP-PDE (24)....
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...Several -subunits like gustducin and transducins belong to the G i/G o family and are involved in specific sensory functions (24, 126)....
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TL;DR: This review focuses on the part of the molecule containing two atoms attached together by a double bond with substituents W-Z which may be found as two isomeric molecules.
Abstract: Organic molecules as well as metal complexes may exist as several geometric isomers1 which display distinct physical properties and chemical reactivities. A molecule containing two atoms (in general, two carbons) attached together by a double bond with substituents W-Z may be found as two isomeric † C.D. dedicates this review to Professor Andrée Marquet as a mark of his admiration and gratitude. * To whom correspondence should be addressed: Tel: (33) 169 08 52 25. Fax: (33) 169 08 90 71. E-mail: christophe.dugave@cea.fr. ‡ Present address: Département de Chimie, Institut de Pharmacologie, Université de Sherbrooke, 3001, 12e Avenue nord, Sherbrooke, Québec, J1H 5N4 Canada. 2475 Chem. Rev. 2003, 103, 2475−2532
849 citations
TL;DR: In this paper, the authors revisited classical heterotrimeric G-protein signaling and explored these new, non-canonical Gprotein signaling pathways, including a receptor-independent Gα nucleotide cycle that regulates cell division.
Abstract: Heterotrimeric G-proteins are intracellular partners of G-protein-coupled receptors (GPCRs). GPCRs act on inactive Gα·GDP/Gβγ heterotrimers to promote GDP release and GTP binding, resulting in liberation of Gα from Gβγ. Gα·GTP and Gβγ target effectors including adenylyl cyclases, phospholipases and ion channels. Signaling is terminated by intrinsic GTPase activity of Gα and heterotrimer reformation — a cycle accelerated by ‘regulators of G-protein signaling’ (RGS proteins). Recent studies have identified several unconventional G-protein signaling pathways that diverge from this standard model. Whereas phospholipase C (PLC) β is activated by Gαq and Gβγ, novel PLC isoforms are regulated by both heterotrimeric and Ras-superfamily G-proteins. An Arabidopsis protein has been discovered containing both GPCR and RGS domains within the same protein. Most surprisingly, a receptor-independent Gα nucleotide cycle that regulates cell division has been delineated in both Caenorhabditis elegans and Drosophila melanogaster. Here, we revisit classical heterotrimeric G-protein signaling and explore these new, non-canonical G-protein signaling pathways.
479 citations
TL;DR: Identification of Rpe65 as the isomerase explains the phenotypes in rpe65-/- knockout mice and in humans with Leber congenital amaurosis.
404 citations
TL;DR: Gene therapy has been successfully used in animal models of these diseases to rescue the function of enzymes involved in chromophore regeneration, restoring vision and hope that multiple inherited retinal diseases will soon be treated by pharmaceutical intervention.
Abstract: Absorption of a photon by an opsin pigment causes isomerization of the chromophore from 11-cis-retinaldehyde to all-transretinaldehyde. Regeneration of visual chromophore following light exposure is dependent on an enzyme pathway called the retinoid or visual cycle. Our understanding of this pathway has been greatly facilitated by the identification of disease-causing mutations in the genes coding for visual cycle enzymes. Defects in nearly every step of this pathway are responsible for human-inherited retinal dystrophies. These retinal dystrophies can be divided into two etiologic groups. One involves the impaired synthesis of visual chromophore. The second involves accumulation of cytotoxic products derived from all-trans-retinaldehyde. Gene therapy has been successfully used in animal models of these diseases to rescue the function of enzymes involved in chromophore regeneration, restoring vision. Dystrophies resulting from impaired chromophore synthesis can also be treated by supplementation with a chromophore analog. Dystrophies resulting from the accumulation of toxic pigments can be treated pharmacologically by inhibiting the visual cycle, or limiting the supply of vitamin A to the eyes. Recent progress in both areas provides hope that multiple inherited retinal diseases will soon be treated by pharmaceutical intervention.
398 citations
References
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TL;DR: Light scattering by small particles as mentioned in this paper, Light scattering by Small Particle Scattering (LPS), Light scattering with small particles (LSC), Light Scattering by Small Parts (LSP),
Abstract: Light scattering by small particles , Light scattering by small particles , مرکز فناوری اطلاعات و اطلاع رسانی کشاورزی
9,737 citations
Book•
01 Dec 1981
TL;DR: Light scattering by small particles as mentioned in this paper, Light scattering by Small Particle Scattering (LPS), Light scattering with small particles (LSC), Light Scattering by Small Parts (LSP),
Abstract: Light scattering by small particles , Light scattering by small particles , مرکز فناوری اطلاعات و اطلاع رسانی کشاورزی
6,623 citations
Book•
01 Jan 1977
TL;DR: The second edition of this biological reference aimed at undergraduates and graduates is as mentioned in this paper, which covers the structure and mechanism of enzymes, creating a guide to the current understanding of enzymology.
Abstract: This is the second edition of this biological reference aimed at undergraduates and graduates. The book covers the structure and mechanism of enzymes, creating a guide to the current understanding of enzymology.
3,231 citations
01 Jan 2003
TL;DR: In this article, the basic physics of elastic light scattering from small particles is studied for the simple case of a homogeneous and isotropic sphere, where the particle velocity and its properties are analyzed.
Abstract: In the laser Doppler and phase Doppler techniques a part of the incident laser light is imaged by the particles onto the detectors. It is this scattered light which carries information about the particle velocity and its properties and thus, the light scattered from small particles plays a central role in the basic physics of these measurement techniques. In recognition of this, the following chapter is devoted to the fundamentals of elastic light scattering from small particles. The simplest case of a homogeneous and isotropic sphere is considered.
2,499 citations
"G proteins and phototransduction." refers background in this paper
...Theoretical analysis shows that, for a dilute suspension of particles whose major dimension is not much greater than the wavelength of the measuring light, the principal factor contributing to a change in the scattering intensity in a particular direction is a change in the mass density of the particles relative to the density of the bulk solution (34, 35)....
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TL;DR: This article reviews many of the more important aspects about the structure, cellular localization, and regulation of each family of phosphodiesterases and places particular emphasis on new information obtained in the last few years about how differential expression andregulation of individual phosphodiesters relate to their function(s) in the body.
Abstract: In the last few years there has been a veritable explosion of knowledge about cyclic nucleotide phosphodiesterases. In particular, the accumulating data showing that there are a large number of different phosphodiesterase isozymes have triggered an equally large increase in interest about these enzymes. At least seven different gene families of cyclic nucleotide phosphodiesterase are currently known to exist in mammalian tissues. Most families contain several distinct genes, and many of these genes are expressed in different tissues as functionally unique alternative splice variants. This article reviews many of the more important aspects about the structure, cellular localization, and regulation of each family of phosphodiesterases. Particular emphasis is placed on new information obtained in the last few years about how differential expression and regulation of individual phosphodiesterase isozymes relate to their function(s) in the body. A substantial discussion of the currently accepted nomenclature is also included. Finally, a brief discussion is included about how the differences among distinct phosphodiesterase isozymes are beginning to be used as the basis for developing therapeutic agents.
1,796 citations
"G proteins and phototransduction." refers background in this paper
...The R∗ activates the transducin by triggering rapid exchange of bound GDP for GTP on the Gαt; this is followed very rapidly by dissociation of the transducin from the R∗, as well as by dissociation of the active Gαt-GTP (or G∗) from Gβγ t. PHOSPHODIESTERASE ACTIVATION At the next step of the cascade Gαt-GTP stimulates the activity of its effector enzyme, the cGMP phosphodiesterase (PDE), also known as PDE6 (27)....
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...PHOSPHODIESTERASE ACTIVATION At the next step of the cascade G αt-GTP stimulates the activity of its effector enzyme, the cGMP phosphodiesterase (PDE), also known as PDE6 (27)....
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