Structural reorganization of parallel actin bundles by crosslinking proteins: Incommensurate states of twist

Homin Shin and Gregory M. Grason
Phys. Rev. E 82, 051919 – Published 15 November 2010

Abstract

We construct a coarse-grained model of parallel actin bundles crosslinked by compact globular bundling proteins, such as fascin and espin, necessary components of filopodial and mechanosensory bundles. Consistent with structural observations of bundles, we find that the optimal geometry for crosslinking is overtwisted, requiring a coherent structural change of the helical geometry of the filaments. We study the linker-dependent thermodynamic transition of bundled actin filaments from their native state to the overtwisted state and map out the “twist-state” phase diagram in terms of the availability as well as the flexibility of crosslinker proteins. We predict that the transition from the uncrosslinked to fully crosslinked state is highly sensitive to linker flexibility: flexible crosslinking smoothly distorts the twist state of bundled filaments, while rigidly crosslinked bundles undergo a phase transition, rapidly overtwisting filaments over a narrow range of free crosslinker concentrations. Additionally, we predict a rich spectrum of intermediate structures, composed of alternating domains of sparsely bound (untwisted) and strongly bound (overtwisted) filaments. This model reveals that subtle differences in crosslinking agents themselves modify not only the detailed structure of parallel actin bundles, but also the thermodynamic pathway by which they form.

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  • Received 28 September 2010

DOI:https://doi.org/10.1103/PhysRevE.82.051919

©2010 American Physical Society

Authors & Affiliations

Homin Shin and Gregory M. Grason

  • Department of Polymer Science and Engineering, University of Massachusetts, Amherst, Massachusetts 01003, USA

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Issue

Vol. 82, Iss. 5 — November 2010

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