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Satoru Kawamura - One of the best experts on this subject based on the ideXlab platform.
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amino acid residues in grk1 grk7 responsible for interaction with s Modulin recoverin
Photochemistry and Photobiology, 2008Co-Authors: Aya Torisawa, Shuji Tachibanaki, Daisuke Arinobu, Satoru KawamuraAbstract:GRK1 is a visual pigment kinase in rods and is essential for inactivation of light-activated rhodopsin. The GRK1 activity is inhibited by binding of the Ca 2+ -bound form of S-Modulin/recoverin. We previously identified the S-Modulin/recoverin site to interact with GRK1. In the present study, we identified its counterpart in GRK1. We synthesized 29 of GRK1 or GRK7 partial peptides that cover the entire sequence of GRK1/GRK7, and examined whether these peptides inhibit S-Modulin/recover-in activity most probably by preoccupying the binding site for GRK1. The inhibition was the greatest with the N-terminal peptide (pi, aa 3-23 in GRK7). On mutation of each of eight amino acid residues highly conserved in the pi region of more than 10 orthologs, the inhibition was significantly reduced in the mutation of Leu 6 , Asn 12 and Tyr 15 . We further examined the binding of the peptides, including mutated ones, to S-Modulin/recoverin with a resonance mirror biosensor. The binding correlated well with the degree of the inhibition by a peptide. The inhibition, therefore, seemed to be due to a direct binding of the kinase peptide to the binding site of active S-Modulin/recoverin. A GRK1 region close to its C-terminus also seemed to be the binding site for S-Modulin/recoverin.
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Amino acid residues in GRK1/GRK7 responsible for interaction with S-Modulin/recoverin.
Photochemistry and photobiology, 2008Co-Authors: Aya Torisawa, Shuji Tachibanaki, Daisuke Arinobu, Satoru KawamuraAbstract:GRK1 is a visual pigment kinase in rods and is essential for inactivation of light-activated rhodopsin. The GRK1 activity is inhibited by binding of the Ca 2+ -bound form of S-Modulin/recoverin. We previously identified the S-Modulin/recoverin site to interact with GRK1. In the present study, we identified its counterpart in GRK1. We synthesized 29 of GRK1 or GRK7 partial peptides that cover the entire sequence of GRK1/GRK7, and examined whether these peptides inhibit S-Modulin/recover-in activity most probably by preoccupying the binding site for GRK1. The inhibition was the greatest with the N-terminal peptide (pi, aa 3-23 in GRK7). On mutation of each of eight amino acid residues highly conserved in the pi region of more than 10 orthologs, the inhibition was significantly reduced in the mutation of Leu 6 , Asn 12 and Tyr 15 . We further examined the binding of the peptides, including mutated ones, to S-Modulin/recoverin with a resonance mirror biosensor. The binding correlated well with the degree of the inhibition by a peptide. The inhibition, therefore, seemed to be due to a direct binding of the kinase peptide to the binding site of active S-Modulin/recoverin. A GRK1 region close to its C-terminus also seemed to be the binding site for S-Modulin/recoverin.
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Amino acid residues of S-Modulin responsible for interaction with rhodopsin kinase.
The Journal of biological chemistry, 2000Co-Authors: Shuji Tachibanaki, Kumiko Nanda, Kenji Sasaki, Koichi Ozaki, Satoru KawamuraAbstract:Abstract S-Modulin in frog or its bovine homologue, recoverin, is a 23-kDa EF-hand Ca2+-binding protein found in rod photoreceptors. The Ca2+-bound form of S-Modulin binds to rhodopsin kinase (Rk) and inhibits its activity. Through this regulation, S-Modulin is thought to modulate the light sensitivity of a rod. In the present study, we tried to identify the interaction site of the Ca2+-bound form of S-Modulin to Rk. First, we mapped roughly the interaction regions by using partial peptides of S-Modulin. The result suggested that a specific region near the amino terminus is the interaction site of S-Modulin. We then identified the essential amino acid residues in this region by using S-Modulin mutant proteins: four amino acid residues (Phe22, Glu26, Phe55, and Thr92) were suggested to interact with Rk. These residues are located in a small closed pocket in the Ca2+-free, inactive form of S-Modulin, but exposed to the surface of the molecule in the Ca2+-bound, active form of S-Modulin. Two additional amino acid residues (Tyr108 and Arg150) were found to be crucial for the Ca2+-dependent conformational changes of S-Modulin.
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Inhibition of rhodopsin phosphorylation by S-Modulins: purification, reconstitution, and assays.
Methods in enzymology, 2000Co-Authors: Satoru KawamuraAbstract:Publisher Summary S-Modulin is a calcium-binding protein found in frog retinal rods. S-Modulin activity was first detected while performing an electrophysiological measurement of cGMP phosphodiesterase (PDE) activity, using a truncated preparation of frog rod outer segment (tROS) that can be internally perfused with a bathing solution. In a later study, it was shown that S-Modulin regulates PDE activation by inhibiting rhodopsin phosphorylation at high Ca 2+ concentrations. At almost the same time that S-Modulin was reported, another Ca 2+ -binding protein was reported. This protein, named recoverin, was found in bovine retina. Later study showed that recoverin is the bovine homolog of S-Modulin. This chapter describes: (1) an electrophysiological method by which to detect S-Modulin activity, (2) purification of S-Modulin and its cone homolog s26 (frog visinin) from frog retina and purification of recoverin from bovine retina, (3) purification of S-Modulin, s26, and recoverin that are expressed in Escherichia coli, and (4) reconstitution and assay of S-Modulin activity.
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Molecular Mechanism of S-Modulin Action: Binding Target and Effect of ATP
Journal of biochemistry, 1997Co-Authors: Naoki Sato, Satoru KawamuraAbstract:S-Modulin is suggested to increase the light sensitivity of rods by inhibiting phosphorylation of light-activated rhodopsin (Rh*) at high Ca2+ concentrations. The inhibition of rhodopsin phosphorylation was almost constant over a wide range of the Rh*/S-Modulin ratio (10(-4)-approximately 10[1]). A 125I-labeled cross-linker that had been conjugated with S-Modulin interacted with a protein of 60 kDa, a molecular mass close to that of frog rhodopsin kinase. These results suggested that the target molecule of S-Modulin is rhodopsin kinase. To investigate the mechanism of the S-Modulin action, we measured rhodopsin phosphorylation in the presence and absence of inhibition by S-Modulin at various timings of ATP addition. The results suggested the following in situ mechanism of S-Modulin action. After light-activation of rhodopsin kinase, the S-Modulin/Ca2+ complex binds to the activated kinase and inhibits the phosphorylation of rhodopsin. The complex, however, does not affect the overall kinetics of the phosphorylation. The inhibition of the kinase by S-Modulin is reversible in terms of the Ca2+ concentration. On the other hand, the kinase activity decreases as a function of time, probably via autophosphorylation.
Fumio Tokunaga - One of the best experts on this subject based on the ideXlab platform.
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Role of carboxyl-terminal charges on S-Modulin membrane affinity and inhibition of rhodopsin phosphorylation.
Biochemistry, 1999Co-Authors: Shinji Matsuda, Osamu Hisatomi, Fumio TokunagaAbstract:S-Modulin shows a higher affinity for urea-stripped frog rod outer segment membranes than s26 (a cone homologue of S-Modulin). NaCl at a concentration of several hundred millimolar reduced the membrane affinity of S-Modulin to the s26 level. Chimeric S-Modulin and s26 whose respective 23 and 29 amino acids at the carboxyl terminus were swapped showed membrane affinites similar to those of s26 and S-Modulin, respectively. The membrane affinity of an S-Modulin mutant lacking C-terminal positive charges was reduced to the s26 level, while another S-Modulin mutant lacking C-terminal negative charges has a higher membrane affinity than wild-type S-Modulin. When the molar ratio of recombinant S-Modulins to rhodopsin is 0.5, there was no large difference in the inhibition efficiency. However, S-Modulin and mutants with high membrane affinities inhibit rhodopsin phosphorylation more efficiently than s26 and mutants with low membrane affinities at the molar ratio of 0.1. These results indicate that the C-terminal ...
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The role of calcium-binding sites in S-Modulin function.
The Journal of biological chemistry, 1998Co-Authors: Shinji Matsuda, Osamu Hisatomi, Tetsuya Ishino, Yuji Kobayashi, Fumio TokunagaAbstract:Abstract S-Modulin controls rhodopsin phosphorylation in a calcium-dependent manner, and it has been suggested that it modulates the light sensitivity of the photoreceptor cell. S-Modulin binds to the ROS membrane at high Ca2+concentration, and N-terminal myristoylation is necessary for this property (the calcium-myristoyl switch). S-Modulin has four EF-hand motifs, of which two (EF-2 and -3) are functional. Here, we report on the roles of EF-2 and -3 in S-Modulin function (calcium binding, membrane association, and inhibition of rhodopsin phosphorylation) by site-directed mutants (E85M and E121M). Surprisingly, E121M, which has a mutation in EF-3, neither binds Ca2+ nor inhibits phosphorylation. In contrast, E85M binds one Ca2+ and has the same membrane affinity as wild-type S-Modulin, but has lost the ability to inhibit rhodopsin phosphorylation. It is suggested that the binding of Ca2+to EF-3 is probably required for EF-2 to be a functional Ca2+-binding site and to induce exposure of the myristoyl group; and that the binding of Ca2+ to EF-2 is important for the interaction with rhodopsin kinase.
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Functional Expression and Characterization of Frog Photoreceptor-Specific Calcium-Binding Proteins
Biochemical and biophysical research communications, 1997Co-Authors: Osamu Hisatomi, Satoru Kawamura, Shinji Matsuda, Tetsuya Ishino, Kouji Yamaguchi, Yuji Kobayashi, Fumio TokunagaAbstract:Abstract S-Modulin (sensitivity-modulating protein) is a photoreceptor-specific calcium-binding protein which plays an important role in the light adaptation process by controlling rhodopsin phosphorylation in rods. S-Modulin and its cone homologue, s26, were expressed at high level (more than 30% of total protein) in Escherichia coli and then purified. They both inhibited rhodopsin phosphorylation in a calcium dependent manner. Myristoylated recombinants of S-Modulin and s26 showed calcium-dependent changes in tryptophan emission spectra with half-maxima at about 0.7 μM free calcium concentration. However, the spectral changes are distinctive from each other, suggesting that there is some difference in the structural change between S-Modulin and s26.
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Photoreceptor Protein s26, a Cone Homologue of S-Modulin in Frog Retina
Journal of Biological Chemistry, 1996Co-Authors: Satoru Kawamura, Osamu Kuwata, Motoyuki Yamada, Osamu Hisatomi, Shinji Matsuda, Fumio TokunagaAbstract:Abstract A frog retinal protein named s26 is a 26-kDa protein found during purification of S-Modulin in frog retina (Kawamura, S. (1992) Photochem. Photobiol. 56, 1173-1180). To identify its role in frog retina, first s26 was purified to nearly homogeneity with three chromatographical steps. Based on the partial amino acid sequences of the proteolysed fragments of s26, we isolated cDNAs that encode s26. The analysis of its amino acid sequence revealed that s26 is an S-Modulin-like protein, while it shows higher homology to visinin. Visinin is a Ca2+-binding protein reported to be present in chicken cones, but its localization in the retina had been a subject in dispute. The present study showed that s26 is present in cone photoreceptors. The study also showed that s26 inhibits phosphorylation of rhodopsin after a light flash at high Ca2+ concentrations as S-Modulin does. From these results, we concluded that s26 is a cone homologue of S-Modulin. The result is consistent with the idea that each type of photoreceptors expresses each cell-type specific version of phototransduction proteins.
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recoverin has s Modulin activity in frog rods
Journal of Biological Chemistry, 1993Co-Authors: Satoru Kawamura, Osamu Hisatomi, Fumio Tokunaga, S Kayada, Chehui KuoAbstract:Abstract In vertebrate photoreceptors, light induces hydrolysis of cGMP by activating cGMP phosphodiesterase (PDE), which results in closure of the cGMP-activated cation channel. During light adaptation, the cytoplasmic Ca2+ concentration decreases, and this decrease is one of the underlying mechanisms of light adaptation. Sensitivity-modulating protein (S-Modulin) is a Ca(2+)-binding protein involved in light adaptation in frog rods; it regulates both the light sensitivity of PDE and the lifetime of activated PDE by controlling rhodopsin phosphorylation in a Ca(2+)-dependent manner. Recoverin has been reported as a Ca(2+)-dependent regulator of guanylate cyclase in bovine rods (Dizhoor, A. M., Ray, S., Kumar, S., Niemi, G., Spencer, M., Brolley, D., Walsh, K. A. Philipov, P. P., Hurley, J. B., and Stryer, L. (1991) Science 251, 915-918). Here, we show that recoverin has similar activity as S-Modulin, and the amino acid sequences of both proteins are similar. The results strongly suggest that recoverin is bovine S-Modulin and regulates PDE activation.
Osamu Hisatomi - One of the best experts on this subject based on the ideXlab platform.
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Role of carboxyl-terminal charges on S-Modulin membrane affinity and inhibition of rhodopsin phosphorylation.
Biochemistry, 1999Co-Authors: Shinji Matsuda, Osamu Hisatomi, Fumio TokunagaAbstract:S-Modulin shows a higher affinity for urea-stripped frog rod outer segment membranes than s26 (a cone homologue of S-Modulin). NaCl at a concentration of several hundred millimolar reduced the membrane affinity of S-Modulin to the s26 level. Chimeric S-Modulin and s26 whose respective 23 and 29 amino acids at the carboxyl terminus were swapped showed membrane affinites similar to those of s26 and S-Modulin, respectively. The membrane affinity of an S-Modulin mutant lacking C-terminal positive charges was reduced to the s26 level, while another S-Modulin mutant lacking C-terminal negative charges has a higher membrane affinity than wild-type S-Modulin. When the molar ratio of recombinant S-Modulins to rhodopsin is 0.5, there was no large difference in the inhibition efficiency. However, S-Modulin and mutants with high membrane affinities inhibit rhodopsin phosphorylation more efficiently than s26 and mutants with low membrane affinities at the molar ratio of 0.1. These results indicate that the C-terminal ...
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The role of calcium-binding sites in S-Modulin function.
The Journal of biological chemistry, 1998Co-Authors: Shinji Matsuda, Osamu Hisatomi, Tetsuya Ishino, Yuji Kobayashi, Fumio TokunagaAbstract:Abstract S-Modulin controls rhodopsin phosphorylation in a calcium-dependent manner, and it has been suggested that it modulates the light sensitivity of the photoreceptor cell. S-Modulin binds to the ROS membrane at high Ca2+concentration, and N-terminal myristoylation is necessary for this property (the calcium-myristoyl switch). S-Modulin has four EF-hand motifs, of which two (EF-2 and -3) are functional. Here, we report on the roles of EF-2 and -3 in S-Modulin function (calcium binding, membrane association, and inhibition of rhodopsin phosphorylation) by site-directed mutants (E85M and E121M). Surprisingly, E121M, which has a mutation in EF-3, neither binds Ca2+ nor inhibits phosphorylation. In contrast, E85M binds one Ca2+ and has the same membrane affinity as wild-type S-Modulin, but has lost the ability to inhibit rhodopsin phosphorylation. It is suggested that the binding of Ca2+to EF-3 is probably required for EF-2 to be a functional Ca2+-binding site and to induce exposure of the myristoyl group; and that the binding of Ca2+ to EF-2 is important for the interaction with rhodopsin kinase.
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Functional Expression and Characterization of Frog Photoreceptor-Specific Calcium-Binding Proteins
Biochemical and biophysical research communications, 1997Co-Authors: Osamu Hisatomi, Satoru Kawamura, Shinji Matsuda, Tetsuya Ishino, Kouji Yamaguchi, Yuji Kobayashi, Fumio TokunagaAbstract:Abstract S-Modulin (sensitivity-modulating protein) is a photoreceptor-specific calcium-binding protein which plays an important role in the light adaptation process by controlling rhodopsin phosphorylation in rods. S-Modulin and its cone homologue, s26, were expressed at high level (more than 30% of total protein) in Escherichia coli and then purified. They both inhibited rhodopsin phosphorylation in a calcium dependent manner. Myristoylated recombinants of S-Modulin and s26 showed calcium-dependent changes in tryptophan emission spectra with half-maxima at about 0.7 μM free calcium concentration. However, the spectral changes are distinctive from each other, suggesting that there is some difference in the structural change between S-Modulin and s26.
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Photoreceptor Protein s26, a Cone Homologue of S-Modulin in Frog Retina
Journal of Biological Chemistry, 1996Co-Authors: Satoru Kawamura, Osamu Kuwata, Motoyuki Yamada, Osamu Hisatomi, Shinji Matsuda, Fumio TokunagaAbstract:Abstract A frog retinal protein named s26 is a 26-kDa protein found during purification of S-Modulin in frog retina (Kawamura, S. (1992) Photochem. Photobiol. 56, 1173-1180). To identify its role in frog retina, first s26 was purified to nearly homogeneity with three chromatographical steps. Based on the partial amino acid sequences of the proteolysed fragments of s26, we isolated cDNAs that encode s26. The analysis of its amino acid sequence revealed that s26 is an S-Modulin-like protein, while it shows higher homology to visinin. Visinin is a Ca2+-binding protein reported to be present in chicken cones, but its localization in the retina had been a subject in dispute. The present study showed that s26 is present in cone photoreceptors. The study also showed that s26 inhibits phosphorylation of rhodopsin after a light flash at high Ca2+ concentrations as S-Modulin does. From these results, we concluded that s26 is a cone homologue of S-Modulin. The result is consistent with the idea that each type of photoreceptors expresses each cell-type specific version of phototransduction proteins.
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recoverin has s Modulin activity in frog rods
Journal of Biological Chemistry, 1993Co-Authors: Satoru Kawamura, Osamu Hisatomi, Fumio Tokunaga, S Kayada, Chehui KuoAbstract:Abstract In vertebrate photoreceptors, light induces hydrolysis of cGMP by activating cGMP phosphodiesterase (PDE), which results in closure of the cGMP-activated cation channel. During light adaptation, the cytoplasmic Ca2+ concentration decreases, and this decrease is one of the underlying mechanisms of light adaptation. Sensitivity-modulating protein (S-Modulin) is a Ca(2+)-binding protein involved in light adaptation in frog rods; it regulates both the light sensitivity of PDE and the lifetime of activated PDE by controlling rhodopsin phosphorylation in a Ca(2+)-dependent manner. Recoverin has been reported as a Ca(2+)-dependent regulator of guanylate cyclase in bovine rods (Dizhoor, A. M., Ray, S., Kumar, S., Niemi, G., Spencer, M., Brolley, D., Walsh, K. A. Philipov, P. P., Hurley, J. B., and Stryer, L. (1991) Science 251, 915-918). Here, we show that recoverin has similar activity as S-Modulin, and the amino acid sequences of both proteins are similar. The results strongly suggest that recoverin is bovine S-Modulin and regulates PDE activation.
Jean-san Chia - One of the best experts on this subject based on the ideXlab platform.
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Activation of Human Valve Interstitial Cells by a Viridians Streptococci Modulin
2016Co-Authors: Induces Chemotaxis, Shoei-shen Wang, Of Mononuclear Cells, Jean-san ChiaAbstract:Infective endocarditis is characterized by inflammatory infiltrates of mononuclear cells in infected cardiac valve leaflets. Todelineate the role of valve interstitial cells (VICs) in leukocyte recruitment,we stimulatedhumanVICs with glucosyltransferase, a Modulin from viridians streptococci. Interstitial cells were activated directly by glu-cosyltransferase in a dose-dependent manner through concerted mitogen-activated protein kinase and nuclear factor–B signaling pathways; activation resulted in up-regulation of synthesis and release of interleukin-6, interleukin-8, ormonocyte chemoattractantprotein–1andenhanced transwellmigrationofU937monocytic cells or primarymononuclear cells. The expressionof glucosyltransferases and activationofVICs (nuclear localization ofRelA)were detected in a ratmodel of experimental endocarditis. Proinflammatory cytokines alsowere detected in VICs from diseased human autopsy specimens but not in VICs from normal specimens. These results indicate that interstitial cells in the cardiac valve can be activated directly by bacterial Modulins to recruit and retain mononuclear cells, likely contributing to the persistent inflammation characteristic of infective endocarditis. Heart valve interstitial cells (VICs) constitute the major stromal population in valve leaflets, and they exhibit di-verse and dynamic phenotypes ranging from fibroblast-like cells to myofibroblasts [1, 2]. Similar to th
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Activation of human valve interstitial cells by a viridians streptococci Modulin induces chemotaxis of mononuclear cells.
The Journal of infectious diseases, 2009Co-Authors: Chia-tung Shun, Chiou-yueh Yeh, Chia-jung Chang, Huei-ting Lien, Jen-yang Chen, Shoei-shen Wang, Jean-san ChiaAbstract:Infective endocarditis is characterized by inflammatory infiltrates of mononuclear cells in infected cardiac valve leaflets. To delineate the role of valve interstitial cells (VICs) in leukocyte recruitment, we stimulated human VICs with glucosyltransferase, a Modulin from viridians streptococci. Interstitial cells were activated directly by glucosyltransferase in a dose-dependent manner through concerted mitogen-activated protein kinase and nuclear factor-kappaB signaling pathways; activation resulted in up-regulation of synthesis and release of interleukin-6, interleukin-8, or monocyte chemoattractant protein-1 and enhanced transwell migration of U937 monocytic cells or primary mononuclear cells. The expression of glucosyltransferases and activation of VICs (nuclear localization of RelA) were detected in a rat model of experimental endocarditis. Proinflammatory cytokines also were detected in VICs from diseased human autopsy specimens but not in VICs from normal specimens. These results indicate that interstitial cells in the cardiac valve can be activated directly by bacterial Modulins to recruit and retain mononuclear cells, likely contributing to the persistent inflammation characteristic of infective endocarditis.
Shinji Matsuda - One of the best experts on this subject based on the ideXlab platform.
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Role of carboxyl-terminal charges on S-Modulin membrane affinity and inhibition of rhodopsin phosphorylation.
Biochemistry, 1999Co-Authors: Shinji Matsuda, Osamu Hisatomi, Fumio TokunagaAbstract:S-Modulin shows a higher affinity for urea-stripped frog rod outer segment membranes than s26 (a cone homologue of S-Modulin). NaCl at a concentration of several hundred millimolar reduced the membrane affinity of S-Modulin to the s26 level. Chimeric S-Modulin and s26 whose respective 23 and 29 amino acids at the carboxyl terminus were swapped showed membrane affinites similar to those of s26 and S-Modulin, respectively. The membrane affinity of an S-Modulin mutant lacking C-terminal positive charges was reduced to the s26 level, while another S-Modulin mutant lacking C-terminal negative charges has a higher membrane affinity than wild-type S-Modulin. When the molar ratio of recombinant S-Modulins to rhodopsin is 0.5, there was no large difference in the inhibition efficiency. However, S-Modulin and mutants with high membrane affinities inhibit rhodopsin phosphorylation more efficiently than s26 and mutants with low membrane affinities at the molar ratio of 0.1. These results indicate that the C-terminal ...
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The role of calcium-binding sites in S-Modulin function.
The Journal of biological chemistry, 1998Co-Authors: Shinji Matsuda, Osamu Hisatomi, Tetsuya Ishino, Yuji Kobayashi, Fumio TokunagaAbstract:Abstract S-Modulin controls rhodopsin phosphorylation in a calcium-dependent manner, and it has been suggested that it modulates the light sensitivity of the photoreceptor cell. S-Modulin binds to the ROS membrane at high Ca2+concentration, and N-terminal myristoylation is necessary for this property (the calcium-myristoyl switch). S-Modulin has four EF-hand motifs, of which two (EF-2 and -3) are functional. Here, we report on the roles of EF-2 and -3 in S-Modulin function (calcium binding, membrane association, and inhibition of rhodopsin phosphorylation) by site-directed mutants (E85M and E121M). Surprisingly, E121M, which has a mutation in EF-3, neither binds Ca2+ nor inhibits phosphorylation. In contrast, E85M binds one Ca2+ and has the same membrane affinity as wild-type S-Modulin, but has lost the ability to inhibit rhodopsin phosphorylation. It is suggested that the binding of Ca2+to EF-3 is probably required for EF-2 to be a functional Ca2+-binding site and to induce exposure of the myristoyl group; and that the binding of Ca2+ to EF-2 is important for the interaction with rhodopsin kinase.
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Functional Expression and Characterization of Frog Photoreceptor-Specific Calcium-Binding Proteins
Biochemical and biophysical research communications, 1997Co-Authors: Osamu Hisatomi, Satoru Kawamura, Shinji Matsuda, Tetsuya Ishino, Kouji Yamaguchi, Yuji Kobayashi, Fumio TokunagaAbstract:Abstract S-Modulin (sensitivity-modulating protein) is a photoreceptor-specific calcium-binding protein which plays an important role in the light adaptation process by controlling rhodopsin phosphorylation in rods. S-Modulin and its cone homologue, s26, were expressed at high level (more than 30% of total protein) in Escherichia coli and then purified. They both inhibited rhodopsin phosphorylation in a calcium dependent manner. Myristoylated recombinants of S-Modulin and s26 showed calcium-dependent changes in tryptophan emission spectra with half-maxima at about 0.7 μM free calcium concentration. However, the spectral changes are distinctive from each other, suggesting that there is some difference in the structural change between S-Modulin and s26.
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Photoreceptor Protein s26, a Cone Homologue of S-Modulin in Frog Retina
Journal of Biological Chemistry, 1996Co-Authors: Satoru Kawamura, Osamu Kuwata, Motoyuki Yamada, Osamu Hisatomi, Shinji Matsuda, Fumio TokunagaAbstract:Abstract A frog retinal protein named s26 is a 26-kDa protein found during purification of S-Modulin in frog retina (Kawamura, S. (1992) Photochem. Photobiol. 56, 1173-1180). To identify its role in frog retina, first s26 was purified to nearly homogeneity with three chromatographical steps. Based on the partial amino acid sequences of the proteolysed fragments of s26, we isolated cDNAs that encode s26. The analysis of its amino acid sequence revealed that s26 is an S-Modulin-like protein, while it shows higher homology to visinin. Visinin is a Ca2+-binding protein reported to be present in chicken cones, but its localization in the retina had been a subject in dispute. The present study showed that s26 is present in cone photoreceptors. The study also showed that s26 inhibits phosphorylation of rhodopsin after a light flash at high Ca2+ concentrations as S-Modulin does. From these results, we concluded that s26 is a cone homologue of S-Modulin. The result is consistent with the idea that each type of photoreceptors expresses each cell-type specific version of phototransduction proteins.