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Struct Dyn. 2016 Jan 14;3(1):012002. doi: 10.1063/1.4940223. eCollection 2016 Jan.

Tropomyosin diffusion over actin subunits facilitates thin filament assembly.

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Computational Biochemistry Group, Interdisciplinary Center for Scientific Computing (IWR), University of Heidelberg , Im Neuenheimer Feld 368, D69120 Heidelberg, Germany.
Department of Physiology and Biophysics, Boston University School of Medicine , 72 East Concord Street, Boston, Massachusetts 02118, USA.
Department of Biological Sciences, University of Massachusetts Lowell , One University Avenue, Lowell, Massachusetts 01854, USA.


Coiled-coil tropomyosin binds to consecutive actin-subunits along actin-containing thin filaments. Tropomyosin molecules then polymerize head-to-tail to form cables that wrap helically around the filaments. Little is known about the assembly process that leads to continuous, gap-free tropomyosin cable formation. We propose that tropomyosin molecules diffuse over the actin-filament surface to connect head-to-tail to partners. This possibility is likely because (1) tropomyosin hovers loosely over the actin-filament, thus binding weakly to F-actin and (2) low energy-barriers provide tropomyosin freedom for 1D axial translation on F-actin. We consider that these unique features of the actin-tropomyosin interaction are the basis of tropomyosin cable formation.

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