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REVIEW: Capping Complex Formation at the Slow-Growing End of the Actin Filament

A. S. Kostyukova1,2

1Institute of Protein Research, Russian Academy of Sciences, 142290 Pushchino, Moscow Region, Russia; E-mail: allakos@gmail.com

2Department of Neuroscience and Cell Biology, RWJMS - UMDNJ, 675 Hoes Lane, Piscataway, NJ 08854, USA; E-mail: kostyuas@umdnj.edu

Received April 23, 2008
Actin filaments are polar; their barbed (fast-growing) and pointed (slow-growing) ends differ in structure and dynamic properties. The slow-growing end is regulated by tropomodulins, a family of capping proteins that require tropomyosins for optimal function. There are four tropomodulin isoforms; their distributions vary depending on tissue type and change during development. The C-terminal half of tropomodulin contains one compact domain represented by alternating α-helices and β-structures. The tropomyosin-independent actin-capping site is located at the C-terminus. The N-terminal half has no regular structure; however, it contains a tropomyosin-dependent actin-capping site and two tropomyosin-binding sites. One tropomodulin molecule can bind two tropomyosin molecules. Effectiveness of tropomodulin binding to tropomyosin depends on the tropomyosin isoform. Regulation of tropomodulin binding at the pointed end as well as capping effectiveness in the presence of specific tropomyosins may affect formation of local cytoskeleton and dynamics of actin filaments in cells.
KEY WORDS: actin filament, capping, tropomodulin, tropomyosin, protein-protein interactions

DOI: 10.1134/S0006297908130075