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Obscurin, a giant sarcomeric Rho guanine nucleotide exchange factor protein involved in sarcomere assembly.

Young P, Ehler E, Gautel M - J. Cell Biol. (2001)

Bottom Line: It was believed that these two proteins represented unique results of protein evolution in vertebrate muscle.Both proteins coassemble during myofibrillogenesis.The presence of a calmodulin-binding IQ motif, and a Rho guanine nucleotide exchange factor domain in the COOH-terminal region suggest that obscurin is involved in Ca(2+)/calmodulin, as well as G protein-coupled signal transduction in the sarcomere.

View Article: PubMed Central - PubMed

Affiliation: European Molecular Biology Laboratory, Structural Biology Division, 69117 Heidelberg, Germany.

ABSTRACT
Vertebrate-striated muscle is assumed to owe its remarkable order to the molecular ruler functions of the giant modular signaling proteins, titin and nebulin. It was believed that these two proteins represented unique results of protein evolution in vertebrate muscle. In this paper we report the identification of a third giant protein from vertebrate muscle, obscurin, encoded on chromosome 1q42. Obscurin is approximately 800 kD and is expressed specifically in skeletal and cardiac muscle. The complete cDNA sequence of obscurin reveals a modular architecture, consisting of >67 intracellular immunoglobulin (Ig)- or fibronectin-3-like domains with multiple splice variants. A large region of obscurin shows a modular architecture of tandem Ig domains reminiscent of the elastic region of titin. The COOH-terminal region of obscurin interacts via two specific Ig-like domains with the NH(2)-terminal Z-disk region of titin. Both proteins coassemble during myofibrillogenesis. During the progression of myofibrillogenesis, all obscurin epitopes become detectable at the M band. The presence of a calmodulin-binding IQ motif, and a Rho guanine nucleotide exchange factor domain in the COOH-terminal region suggest that obscurin is involved in Ca(2+)/calmodulin, as well as G protein-coupled signal transduction in the sarcomere.

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Localization of endogenous obscurin. Localization of endogenous obscurin (green with all antibodies) in neonatal rat cardiomyocytes demonstrates all four obscurin epitopes in association with the sarcomeric M-band (arrowheads). Obscurin visualized with α-Ob48–49 colocalizes with myomesin (red in A–C) at the M-band (A) similar to the staining observed with α-Ob51–52 (B) and α–Ob-DH (C). The epitope of α-Ob19–20 is first detected after birth and is initially only weakly expressed (D), counterstain with the titin Z-disk antibody T12 in red). Bar, 5 μm.
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fig6: Localization of endogenous obscurin. Localization of endogenous obscurin (green with all antibodies) in neonatal rat cardiomyocytes demonstrates all four obscurin epitopes in association with the sarcomeric M-band (arrowheads). Obscurin visualized with α-Ob48–49 colocalizes with myomesin (red in A–C) at the M-band (A) similar to the staining observed with α-Ob51–52 (B) and α–Ob-DH (C). The epitope of α-Ob19–20 is first detected after birth and is initially only weakly expressed (D), counterstain with the titin Z-disk antibody T12 in red). Bar, 5 μm.

Mentions: In neonatal rat cardiomyocytes, endogenous obscurin was found to localize at the M-band as detected by all four antibodies. Occasional weak Z-disk staining was observed only with α-Ob48–49, which binds to the titin binding site (Fig. 6) . Since myofibrillogenesis in vivo is not always faithfully reflected in detail in cultured cardiac myocytes (Ehler et al., 1999), we used the same antibodies on whole-mount preparations of embryonic chicken, mouse and rat hearts spanning early to late stages of heart development.


Obscurin, a giant sarcomeric Rho guanine nucleotide exchange factor protein involved in sarcomere assembly.

Young P, Ehler E, Gautel M - J. Cell Biol. (2001)

Localization of endogenous obscurin. Localization of endogenous obscurin (green with all antibodies) in neonatal rat cardiomyocytes demonstrates all four obscurin epitopes in association with the sarcomeric M-band (arrowheads). Obscurin visualized with α-Ob48–49 colocalizes with myomesin (red in A–C) at the M-band (A) similar to the staining observed with α-Ob51–52 (B) and α–Ob-DH (C). The epitope of α-Ob19–20 is first detected after birth and is initially only weakly expressed (D), counterstain with the titin Z-disk antibody T12 in red). Bar, 5 μm.
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC2196875&req=5

fig6: Localization of endogenous obscurin. Localization of endogenous obscurin (green with all antibodies) in neonatal rat cardiomyocytes demonstrates all four obscurin epitopes in association with the sarcomeric M-band (arrowheads). Obscurin visualized with α-Ob48–49 colocalizes with myomesin (red in A–C) at the M-band (A) similar to the staining observed with α-Ob51–52 (B) and α–Ob-DH (C). The epitope of α-Ob19–20 is first detected after birth and is initially only weakly expressed (D), counterstain with the titin Z-disk antibody T12 in red). Bar, 5 μm.
Mentions: In neonatal rat cardiomyocytes, endogenous obscurin was found to localize at the M-band as detected by all four antibodies. Occasional weak Z-disk staining was observed only with α-Ob48–49, which binds to the titin binding site (Fig. 6) . Since myofibrillogenesis in vivo is not always faithfully reflected in detail in cultured cardiac myocytes (Ehler et al., 1999), we used the same antibodies on whole-mount preparations of embryonic chicken, mouse and rat hearts spanning early to late stages of heart development.

Bottom Line: It was believed that these two proteins represented unique results of protein evolution in vertebrate muscle.Both proteins coassemble during myofibrillogenesis.The presence of a calmodulin-binding IQ motif, and a Rho guanine nucleotide exchange factor domain in the COOH-terminal region suggest that obscurin is involved in Ca(2+)/calmodulin, as well as G protein-coupled signal transduction in the sarcomere.

View Article: PubMed Central - PubMed

Affiliation: European Molecular Biology Laboratory, Structural Biology Division, 69117 Heidelberg, Germany.

ABSTRACT
Vertebrate-striated muscle is assumed to owe its remarkable order to the molecular ruler functions of the giant modular signaling proteins, titin and nebulin. It was believed that these two proteins represented unique results of protein evolution in vertebrate muscle. In this paper we report the identification of a third giant protein from vertebrate muscle, obscurin, encoded on chromosome 1q42. Obscurin is approximately 800 kD and is expressed specifically in skeletal and cardiac muscle. The complete cDNA sequence of obscurin reveals a modular architecture, consisting of >67 intracellular immunoglobulin (Ig)- or fibronectin-3-like domains with multiple splice variants. A large region of obscurin shows a modular architecture of tandem Ig domains reminiscent of the elastic region of titin. The COOH-terminal region of obscurin interacts via two specific Ig-like domains with the NH(2)-terminal Z-disk region of titin. Both proteins coassemble during myofibrillogenesis. During the progression of myofibrillogenesis, all obscurin epitopes become detectable at the M band. The presence of a calmodulin-binding IQ motif, and a Rho guanine nucleotide exchange factor domain in the COOH-terminal region suggest that obscurin is involved in Ca(2+)/calmodulin, as well as G protein-coupled signal transduction in the sarcomere.

Show MeSH
Related in: MedlinePlus