Tube Width Fluctuations in F-Actin Solutions

Abstract

We determine the statistics of the local tube width in F-actin solutions, beyond the usually reported mean value. Our experimental observations are explained by a segment fluid theory based on the binary collision approximation. In this systematic generalization of the standard mean-field approach, effective polymer segments interact via a potential representing the topological constraints. The analytically predicted universal tube width distribution with a stretched tail is in good agreement with the data.

Distribution of transverse chain fluctuations in harmonically confined semiflexible polymers

“…The distributions of tube radii have a stretched Gaussian appearance, but are not quite the same in the two experiments, and they can be well fit to theoretical curves obtained from models based, in the case of Ref. 5, on the statistics of a single worm-like chain confined to a potential determined self-consistently by a binary collision approximation, and in the case of Ref. 6, on a phenomenological scaling approach applied to a fluid of thin rods.…”

“…(9)], deviates from Gaussian behavior. It is the distribution of tube radii that has been measured experimentally, in one case by Glaser et al 5 whose data are well-fit by a function of the form r −a exp (−A/r b ), where a, A, and b are positive constants, and r is the tube radius, and in another by Wang et al 6 whose data are well-fit by a function that appears to be Gaussian at small r and exponential at large r. While Eq. (9) is algebraically distinct from the expressions in Refs.…”

“…3 And despite the model's heuristic and phenomenological character, its basic premise, that polymers slither around in tubes when they are entangled with each other, seems to have been more or less conclusively validated by experiment. [4][5][6] However, the tubes that surround entangled polymers, being formed by a matrix of other mobile chains, are not permanent, and the surfaces that define them change randomly in time, producing stochastic fluctuations in the average tube diameter. Quantitative information about these tube width fluctuations has been obtained from two recent experiments, 5,6 both based on the imaging, by confocal microscopy, of long, densely packed and fluorescently labelled filaments of the protein F-actin, a semiflexible biopolymer.…”

“…[4][5][6] However, the tubes that surround entangled polymers, being formed by a matrix of other mobile chains, are not permanent, and the surfaces that define them change randomly in time, producing stochastic fluctuations in the average tube diameter. Quantitative information about these tube width fluctuations has been obtained from two recent experiments, 5,6 both based on the imaging, by confocal microscopy, of long, densely packed and fluorescently labelled filaments of the protein F-actin, a semiflexible biopolymer. In both sets of experiments, time-averaged measurements of the fluorescence intensity at different points along a given filament in directions transverse to the chain contour reveal significant fluctuations across the length of the chain.…”

Fluctuations of Stiff Polymers and Cell Mechanics

“…This controversy results in part from the close match of the scaling exponents in the BCA (R ∝ c −3/5 ) and the EMA (R ∝ c −1/2 ), suggesting that an unambiguous distinction between the two power-laws is extremely difficult to establish experimentally (Tassieri et al, 2008). In addition, respective conclusions must be drawn with care, since experiments typically yield skewed distributions of the tube radius, rendering an interpretation in terms of mere average values problematic (Wang et al, 2010;Glaser et al, 2010).…”