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Titin Extensibility In Situ: Entropic Elasticity of Permanently Folded and Permanently Unfolded Molecular Segments

Abstract. Titin (also known as connectin) is a giant protein that spans half of the striated muscle sarcomere. In the I-band titin extends as the sarcomere is stretched, developing what is known as passive force. The I-band region of titin contains tandem Ig segments (consisting of serially linked i...

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Autores principales: Trombitás, Karoly, Greaser, Marion, Labeit, Siegfried, Jin, Jian-Ping, Kellermayer, Miklós, Helmes, Michiel, Granzier, Henk
Formato: Texto
Lenguaje:English
Publicado: The Rockefeller University Press 1998
Materias:
Acceso en línea:https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2141751/
https://www.ncbi.nlm.nih.gov/pubmed/9472037
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author Trombitás, Karoly
Greaser, Marion
Labeit, Siegfried
Jin, Jian-Ping
Kellermayer, Miklós
Helmes, Michiel
Granzier, Henk
author_facet Trombitás, Karoly
Greaser, Marion
Labeit, Siegfried
Jin, Jian-Ping
Kellermayer, Miklós
Helmes, Michiel
Granzier, Henk
author_sort Trombitás, Karoly
collection PubMed
description Abstract. Titin (also known as connectin) is a giant protein that spans half of the striated muscle sarcomere. In the I-band titin extends as the sarcomere is stretched, developing what is known as passive force. The I-band region of titin contains tandem Ig segments (consisting of serially linked immunoglobulin-like domains) with the unique PEVK segment in between (Labeit, S., and B. Kolmerer. 1995. Science. 270:293–296). Although the tandem Ig and PEVK segments have been proposed to behave as stiff and compliant springs, respectively, precise experimental testing of the hypothesis is still needed. Here, sequence-specific antibodies were used to mark the ends of the tandem Ig and PEVK segments. By following the extension of the segments as a function of sarcomere length (SL), their respective contributions to titin's elastic behavior were established. In slack sarcomeres (∼2.0 μm) the tandem Ig and PEVK segments were contracted. Upon stretching sarcomeres from ∼2.0 to 2.7 μm, the “contracted” tandem Ig segments straightened while their individual Ig domains remained folded. When sarcomeres were stretched beyond ∼2.7 μm, the tandem Ig segments did not further extend, instead PEVK extension was now dominant. Modeling tandem Ig and PEVK segments as entropic springs with different bending rigidities (Kellermayer, M., S. Smith, H. Granzier, and C. Bustamante. 1997. Science. 276:1112–1116) indicated that in the physiological SL range (a) the Ig-like domains of the tandem Ig segments remain folded and (b) the PEVK segment behaves as a permanently unfolded polypeptide. Our model provides a molecular basis for the sequential extension of titin's different segments. Initially, the tandem Ig segments extend at low forces due to their high bending rigidity. Subsequently, extension of the PEVK segment occurs only upon reaching sufficiently high external forces due to its low bending rigidity. The serial linking of tandem Ig and PEVK segments with different bending rigidities provides a unique passive force–SL relation that is not achievable with a single elastic segment.
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spelling pubmed-21417512008-05-01 Titin Extensibility In Situ: Entropic Elasticity of Permanently Folded and Permanently Unfolded Molecular Segments Trombitás, Karoly Greaser, Marion Labeit, Siegfried Jin, Jian-Ping Kellermayer, Miklós Helmes, Michiel Granzier, Henk J Cell Biol Article Abstract. Titin (also known as connectin) is a giant protein that spans half of the striated muscle sarcomere. In the I-band titin extends as the sarcomere is stretched, developing what is known as passive force. The I-band region of titin contains tandem Ig segments (consisting of serially linked immunoglobulin-like domains) with the unique PEVK segment in between (Labeit, S., and B. Kolmerer. 1995. Science. 270:293–296). Although the tandem Ig and PEVK segments have been proposed to behave as stiff and compliant springs, respectively, precise experimental testing of the hypothesis is still needed. Here, sequence-specific antibodies were used to mark the ends of the tandem Ig and PEVK segments. By following the extension of the segments as a function of sarcomere length (SL), their respective contributions to titin's elastic behavior were established. In slack sarcomeres (∼2.0 μm) the tandem Ig and PEVK segments were contracted. Upon stretching sarcomeres from ∼2.0 to 2.7 μm, the “contracted” tandem Ig segments straightened while their individual Ig domains remained folded. When sarcomeres were stretched beyond ∼2.7 μm, the tandem Ig segments did not further extend, instead PEVK extension was now dominant. Modeling tandem Ig and PEVK segments as entropic springs with different bending rigidities (Kellermayer, M., S. Smith, H. Granzier, and C. Bustamante. 1997. Science. 276:1112–1116) indicated that in the physiological SL range (a) the Ig-like domains of the tandem Ig segments remain folded and (b) the PEVK segment behaves as a permanently unfolded polypeptide. Our model provides a molecular basis for the sequential extension of titin's different segments. Initially, the tandem Ig segments extend at low forces due to their high bending rigidity. Subsequently, extension of the PEVK segment occurs only upon reaching sufficiently high external forces due to its low bending rigidity. The serial linking of tandem Ig and PEVK segments with different bending rigidities provides a unique passive force–SL relation that is not achievable with a single elastic segment. The Rockefeller University Press 1998-02-23 /pmc/articles/PMC2141751/ /pubmed/9472037 Text en This article is distributed under the terms of an Attribution–Noncommercial–Share Alike–No Mirror Sites license for the first six months after the publication date (see http://www.rupress.org/terms). After six months it is available under a Creative Commons License (Attribution–Noncommercial–Share Alike 4.0 Unported license, as described at http://creativecommons.org/licenses/by-nc-sa/4.0/).
spellingShingle Article
Trombitás, Karoly
Greaser, Marion
Labeit, Siegfried
Jin, Jian-Ping
Kellermayer, Miklós
Helmes, Michiel
Granzier, Henk
Titin Extensibility In Situ: Entropic Elasticity of Permanently Folded and Permanently Unfolded Molecular Segments
title Titin Extensibility In Situ: Entropic Elasticity of Permanently Folded and Permanently Unfolded Molecular Segments
title_full Titin Extensibility In Situ: Entropic Elasticity of Permanently Folded and Permanently Unfolded Molecular Segments
title_fullStr Titin Extensibility In Situ: Entropic Elasticity of Permanently Folded and Permanently Unfolded Molecular Segments
title_full_unstemmed Titin Extensibility In Situ: Entropic Elasticity of Permanently Folded and Permanently Unfolded Molecular Segments
title_short Titin Extensibility In Situ: Entropic Elasticity of Permanently Folded and Permanently Unfolded Molecular Segments
title_sort titin extensibility in situ: entropic elasticity of permanently folded and permanently unfolded molecular segments
topic Article
url https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2141751/
https://www.ncbi.nlm.nih.gov/pubmed/9472037
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