Role of tropomyosin isoforms in the calcium sensitivity of striated muscle thin filamentsReport as inadecuate

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Journal of Muscle Research and Cell Motility

, Volume 28, Issue 1, pp 49–58

First Online: 14 April 2007Received: 05 February 2007Accepted: 20 March 2007DOI: 10.1007-s10974-007-9103-z

Cite this article as: Boussouf, S.E., Maytum, R., Jaquet, K. et al. J Muscle Res Cell Motil 2007 28: 49. doi:10.1007-s10974-007-9103-z


We have expressed α and β isoforms of mammalian striated muscle tropomyosin Tm and α-Tm carrying the D175N or E180G cardiomyopathy mutations. In each case the Tm carries an Ala-Ser N-terminal extension to mimic the acetylation of the native Tm. We show that these Ala-Ser modified proteins are good analogues of the native Tm in the assays used here. We go on to use an in vitro kinetic approach to define the assembly of actin filaments with the Tm isoforms with either a cardiac or a skeletal muscle troponin cTn, skTn. With skTn the calcium sensitivity of the actin filament is the same for α and β-Tm and there is little change with the mutant Tms. For cTn switching from α to β-Tm causes an increase of calcium sensitivity of 0.2 pCa units. D175N is very similar to the wild type α-Tm and E180G shows a small increase in calcium sensitivity of about 0.1 pCa unit. The formation of the switched-off blocked-state of the actin filament is independent of the Tm isoform but does differ for cardiac versus skeletal Tn. The in vitro assays developed here provide a novel, simple and efficient method for assaying the behaviour of expressed thin filament proteins.

KeywordsActin Ca-regulation Skeletal muscle Cardiac muscle Cardiomyopathies AbbreviationsTmTropomyosin

α-TmAlpha tropomyosin

β-TmBeta tropomyosin


S1Myosin subfragment 1

skTnSkeletal muscle troponin

cTnCardiac muscle troponin

PKAProtein kinase A

FHCFamilial Hypertrophic Cardiomyopathies

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Author: Sabrina E. Boussouf - Robin Maytum - Kornelia Jaquet - Michael A. Geeves


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