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Issue 13, 2012
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Chiral structure of F-actin bundle formed by multivalent counterions

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The mechanism of multivalent counterion-induced bundle formation by filamentous actin (F-actin) is studied using a coarse-grained model and molecular dynamics simulations. Real diameter size, helically ordered charge distribution and twist rigidity of F-actin are taken into account in our model. The attraction between parallel F-actins induced by multivalent counterions is studied in detail and it is found that the maximum attraction occurs between their closest charged domains. The model F-actins aggregate due to the like-charge attraction and form closely packed bundles. Counterions are mostly distributed in the narrowest gaps between neighboring F-actins inside the bundles and the channels between three adjacent F-actins correspond to the low density of the counterions. Density of the counterions varies periodically with a wave length comparable to the separation between consecutive G-actin monomers along the actin polymers. Long-lived defects in the hexagonal order of F-actins in the bundles are observed; their number increases with increasing the bundle size. A combination of electrostatic interactions and twist rigidity has been found not to change the symmetry of the F-actin helical conformation from the native Image ID:c2sm07104e-t1.gif symmetry. Calculation of the zero-temperature energy of hexagonally ordered model F-actins with the charge of the counterions distributed as columns of charge domains representing counterion charge density waves has shown that helical symmetries commensurate with the hexagonal lattice correspond to local minima of the energy of the system. The global minimum of energy corresponds to Image ID:c2sm07104e-t2.gif symmetry with the columns of charge domains arranged in the narrowest gaps between the neighboring F-actins.

Graphical abstract: Chiral structure of F-actin bundle formed by multivalent counterions

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Publication details

The article was received on 03 Nov 2011, accepted on 18 Jan 2012 and first published on 20 Feb 2012

Article type: Paper
DOI: 10.1039/C2SM07104E
Citation: Soft Matter, 2012,8, 3649-3656
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    Chiral structure of F-actin bundle formed by multivalent counterions

    S. Mohammadinejad, R. Golestanian and H. Fazli, Soft Matter, 2012, 8, 3649
    DOI: 10.1039/C2SM07104E

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