Amino Acid Residues of S-modulin Responsible for Interaction with Rhodopsin Kinase

Tachibanaki, Shuji; Nanda, Kumiko; Sasaki, Kenji; Ozaki, Koichi; Kawamura, Sadao

doi:10.1074/jbc.275.5.3313

Cited by 34 publications

(34 citation statements)

References 38 publications

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“…The EF-hand domain 1, which cannot itself coordinate metal, has been shown to be crucial for GCAP-1 and GCAP-2 interaction with RetGC (18 -20, 30, 42) and in some other NCS proteins for interaction with their targets (43)(44)(45). We found a striking effect of EF-hand 2 occupation by Mg 2ϩ on the conformation of the EF-hand 1 domain, revealed by its fluorescence spectra (Fig.…”

Section: Discussionmentioning

confidence: 63%

Activation and Inhibition of Photoreceptor Guanylyl Cyclase by Guanylyl Cyclase Activating Protein 1 (GCAP-1)

Peshenko

Dizhoor

2007

Journal of Biological Chemistry

164

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Calcium is the major regulator of the physiological responses in photoreceptor cells. Calcium enters outer segments of vertebrate photoreceptors through cGMP-gated Na ϩ /Ca 2ϩ channels in the outer segment plasma membrane and is continuously removed from the outer segment by a light-independent Na re-enters the outer segments and the Ca 2ϩ -bound GCAPs decelerate cGMP synthesis.GCAPs are recoverin-like neuronal calcium-binding proteins, also referred to as the neuronal calcium sensors (NCS) family, a part of a larger superfamily of EF-hand Ca 2ϩ -binding proteins (12)(13)(14)(15)(16). Like all other members of that superfamily GCAPs have Ca 2ϩ -binding EF-hand domains of the helix-loophelix structure. The metal-binding loop in the NCS proteins is traditionally defined as 12 sequential amino acid residues, of which 6 residues provide the oxygen atoms required for the metal coordination, including the invariant first and the last coordinating residues, Asp and Glu, respectively. The N-terminal EF-hand domains in GCAP-1 and GCAP-2 lack some of the oxygen-containing groups required for coordinating the metal ion (17), but are instead required for their interaction with . We previously found that in the conditions that mimic light-adapted or dark-adapted photoreceptors, three other EF-hands in GCAP-1 are predominantly filled by either Mg 2ϩ or Ca 2ϩ , respectively (21, 22). There are multiple reports that substitutions of the first and last coordinating amino acids inactivate EF-hands in NCS proteins (17,(22)(23)(24)(25). Among these are the observations that inactivation of all three metal-binding EF-hands in GCAP-2 by substitution of the last Glu in EF-hands 2 and 3 with Gln and the first Asp in the EF-hand 4 with Asn make GCAP-2 a constitutive, insensitive to Ca 2ϩ activator of RetGC (24). A similar effect was observed for GCAP-1, whose EF-hands were disabled by substitution of the last Glu in the Ca 2ϩ -binding loop with Asp (25). Those observations lead to the perception that metal-free GCAPs are the activators of RetGC and that GCAPs undergo transition from Ca 2ϩ -bound to the metal-free form between dark and light. However, our recent study of metal-binding * This work was supported in part by National Institutes of Health Grant EY11522 and the Pennsylvania Lions Sight Conservation and Eye Research Foundation. The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked "advertisement" in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.

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Section: Discussionmentioning

confidence: 63%

Activation and Inhibition of Photoreceptor Guanylyl Cyclase by Guanylyl Cyclase Activating Protein 1 (GCAP-1)

Peshenko

Dizhoor

2007

Journal of Biological Chemistry

164

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“…A similar approach was used to understand the different capabilities of the same recoverin variants to inhibit rhodopsin kinase in a Ca 2ϩ -dependent manner. In a recent mutational study on the frog recoverin homolog S-modulin, Tachibanaki et al (43) identified seven conserved amino acid residues that were proposed to constitute an interaction surface for rhodopsin kinase. Based on the degree of preservation of Ca 2ϩ -induced conformational changes as assessed by CD spectroscopy, the authors defined "probable" (residues Phe 23 , Glu 27 , Phe 56 , and Thr 93 ) and "possible" (residues Thr 21 , Phe 57 , and Lys 101 ) interaction sites.…”

Section: Discussionmentioning

confidence: 99%

Impact of N-terminal Myristoylation on the Ca2+-dependent Conformational Transition in Recoverin

Weiergräber

Senin

Philippov

et al. 2003

Journal of Biological Chemistry

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Recoverin is a Ca2؉ -regulated signal transduction modulator found in vertebrate retina that has been shown to undergo dramatic conformational changes upon Ca 2؉ binding to its two functional EF-hand motifs. To elucidate the differential impact of the N-terminal myristoylation as well as occupation of the two Ca 2؉ binding sites on recoverin structure and function, we have investigated a non-myristoylated E85Q mutant exhibiting virtually no Ca 2؉ binding to EF-2. Crystal structures of the mutant protein as well as the non-myristoylated wild-type have been determined. Although the non-myristoylated E85Q mutant does not display any functional activity, its three-dimensional structure in the presence of Ca 2؉ resembles the myristoylated wildtype with two Ca 2؉ but is quite dissimilar from the myristoylated E85Q mutant. We conclude that the N-terminal myristoyl modification significantly stabilizes the conformation of the Ca 2؉ -free protein (i.e. the T conformation) during the stepwise transition toward the fully Ca 2؉ -occupied state. On the basis of these observations, a refined model for the role of the myristoyl group as an intrinsic allosteric modulator is proposed.Recoverin belongs to an ancient family of calcium-binding proteins termed the neuronal calcium sensor family (1, 2) and is mainly expressed in vertebrate photoreceptor cells (3, 4). The 23-kDa protein is composed of two domains, each of them harboring one non-functional and one functional EF-hand helix-loop-helix motif (5). Vertebrate photoreceptor cells respond to illumination by a decrease of the intracellular transmitters of excitation and adaptation, cGMP and Ca 2ϩ , respectively. In the dark, at high Ca 2ϩ concentration, the two functional EFhands of recoverin (EF-2 and -3) are occupied by Ca 2ϩ (6 -8). In this state, recoverin is able to inhibit the G-protein-coupled receptor kinase GRK1 1 (rhodopsin kinase), thereby prolonging the lifetime of photoexcited rhodopsin (9 -12). Upon illumination, decrease of cytoplasmic Ca 2ϩ causes this inhibition to be relieved. This regulatory circuit is thought to be one out of several Ca 2ϩ -dependent mechanisms that control adaptation of phototransduction to changing background light intensities (13,14).At its N terminus recoverin is heterogeneously acylated, the prevailing modification being a myristoyl chain (15). The observation of a Ca 2ϩ -dependent partitioning of recoverin to membranes led to the proposal that it underwent a Ca 2ϩ -myristoyl switch (16). The mechanics of this switch were unraveled by determining the solution structures of Ca 2ϩ -free and Ca 2ϩ -bound myristoylated recoverin via NMR spectroscopy. In the Ca 2ϩ -free state of recoverin (T state) the myristoyl moiety is buried within a hydrophobic pocket, whereas in the Ca 2ϩ -bound form (R state), the acyl group is extruded and thus available for interaction with other proteins or insertion into a lipid bilayer (17-19). Moreover, the myristoyl chain has been proposed to act as an intrinsic allosteric effector modifying the conformational...

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“…The kinases were affinity-purified with nonacylated S-modulin as described in ref. 22 and concentrated in the K-gluc buffer. The amount of the expressed protein was quantified with Coomassie brilliant blue staining after SDS͞PAGE, using BSA as a standard.…”

Section: Expression and Purification Of Recombinant Rod Kinase And Conementioning

confidence: 99%

Highly effective phosphorylation by G protein-coupled receptor kinase 7 of light-activated visual pigment in cones

Tachibanaki

Arinobu

Tsushima

et al. 2005

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

Self Cite

123

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Cone photoreceptors show briefer photoresponses than rod photoreceptors. Our previous study showed that visual pigment phosphorylation, a quenching mechanism of light-activated visual pigment, is much more rapid in cones than in rods. Here, we measured the early time course of this rapid phosphorylation with good time resolution and directly compared it with the photoresponse time course in cones. At the time of photoresponse recovery, almost two phosphates were incorporated into a bleached cone pigment molecule, which indicated that the visual pigment phosphorylation coincides with the photoresponse recovery. The rapid phosphorylation in cones is attributed to very high activity of visual pigment kinase [G protein-coupled receptor kinase (GRK) 7] in cones. Because of this high activity, cone pigment is readily phosphorylated at very high bleach levels, which probably explains why cone photoresponses recover quickly even after a very bright light and do not saturate under intense background light. The high GRK7 activity is brought about by high content of a highly potent enzyme. The expression level of GRK7 was 10 times higher than that of rod kinase (GRK1), and the specific activity of a single GRK7 molecule was Ϸ10 times higher than that of GRK1. The specific activity of GRK7 is the highest among the GRKs so far known. Our result seems to explain the response characteristics of cone photoreceptors in many aspects, including the nonsaturation of the cone responses during daylight vision.rod ͉ photoreceptors ͉ retina ͉ phototransduction O ur visual system consists of two components: rods and cones (1, 2). These photoreceptors differ in their light sensitivity so that rods mediate twilight vision, and cones mediate daylight vision. Rods and cones are distinguished not only in their light sensitivity, but also in other response characteristics. The photoresponse time course is much briefer in cones, which improves the time resolution of our daylight vision greatly. Rods are saturated with bright background light and do not respond to more intense light (3). In contrast, cones are not saturated and respond to very bright light (4, 5). The molecular mechanisms underlying in the differences of these response characteristics are not yet known. In previous biochemical studies on the cone phototransduction mechanism, only slight quantitative differences were known in the transduction components between rods and cones (6-8).In our previous study, we obtained a large quantity of isolated cones (enough to perform biochemistry) and showed that transducin activation and cGMP phosphodiesterase activation, the reactions involved in the generation of a photoresponse, are less efficient in cones (9). These findings reasonably explained the lower light sensitivity in cones. Another remarkable difference was found in the phosphorylation of light-activated visual pigment. When light-activated, visual pigment is phosphorylated by a class of kinase known as rhodopsin kinase (rod kinase or G protein-coupled receptor kinase (GRK) 1) in...

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Amino Acid Residues of S-modulin Responsible for Interaction with Rhodopsin Kinase

Cited by 34 publications

References 38 publications

Activation and Inhibition of Photoreceptor Guanylyl Cyclase by Guanylyl Cyclase Activating Protein 1 (GCAP-1)

Activation and Inhibition of Photoreceptor Guanylyl Cyclase by Guanylyl Cyclase Activating Protein 1 (GCAP-1)

Impact of N-terminal Myristoylation on the Ca2+-dependent Conformational Transition in Recoverin

Highly effective phosphorylation by G protein-coupled receptor kinase 7 of light-activated visual pigment in cones

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