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Regulation of Actin Filament Length by Muscle Isoforms of Tropomyosin and Cofilin.

Authors
  • Robaszkiewicz, Katarzyna1
  • Śliwinska, Małgorzata1
  • Moraczewska, Joanna1
  • 1 Department of Biochemistry and Cell Biology, Faculty of Biological Sciences, Kazimierz Wielki University in Bydgoszcz, 85-671 Bydgoszcz, Poland. , (Poland)
Type
Published Article
Journal
International Journal of Molecular Sciences
Publisher
MDPI AG
Publication Date
Jun 16, 2020
Volume
21
Issue
12
Identifiers
DOI: 10.3390/ijms21124285
PMID: 32560136
Source
Medline
Keywords
Language
English
License
Unknown

Abstract

In striated muscle the extent of the overlap between actin and myosin filaments contributes to the development of force. In slow twitch muscle fibers actin filaments are longer than in fast twitch fibers, but the mechanism which determines this difference is not well understood. We hypothesized that tropomyosin isoforms Tpm1.1 and Tpm3.12, the actin regulatory proteins, which are specific respectively for fast and slow muscle fibers, differently stabilize actin filaments and regulate severing of the filaments by cofilin-2. Using in vitro assays, we showed that Tpm3.12 bound to F-actin with almost 2-fold higher apparent binding constant (Kapp) than Tpm1.1. Cofilin2 reduced Kapp of both tropomyosin isoforms. In the presence of Tpm1.1 and Tpm3.12 the filaments were longer than unregulated F-actin by 25% and 40%, respectively. None of the tropomyosins affected the affinity of cofilin-2 for F-actin, but according to the linear lattice model both isoforms increased cofilin-2 binding to an isolated site and reduced binding cooperativity. The filaments decorated with Tpm1.1 and Tpm3.12 were severed by cofilin-2 more often than unregulated filaments, but depolymerization of the severed filaments was inhibited. The stabilization of the filaments by Tpm3.12 was more efficient, which can be attributed to lower dynamics of Tpm3.12 binding to actin.

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