Chain Dynamics, Mesh Size, and Diffusive Transport in Networks of Polymerized Actin: A Quasielastic Light Scattering and Microfluorescence Study

Dynamical (chain excitations, reptational diffusion) and structural (mesh size) properties of semidilute solutions (gels) of polymerized actin and their concentration dependencies were studied by quasielastic light scattering (QELS) and microfluorescence experiments. By QELS we could measure the internal dynamics of single chains. The fact that only internal single-chain dynamics are observed by QELS is a consequence of the inverse of the scattering vector q (6 X 10⁴cm^-1< q < 3 X 10⁵cm^-1) being small compared to both the average contour length of the actin filaments (>30 μm), which was estimated from reptational diffusion, and the average mesh size ξ of the network. That QELS measures internal dynamics of single chains is also shown by the insensitivity of the measured dynamic structure factor to cross-linking by a-actinin. For the range of actin concentrations, 0.08 mg/mL < ca< 0.37 mg/mL, and scattering angles, 20° < 0 < 150°, studied in this work, the dynamic structure factor S(q,t) of the polymer chains decays like S(q,t) <« exp(-Γq⁽⁰⁾£) at short times (Γq^(o)t « 1). At long times (Γq⁽⁰⁾t » 1) it follows the relation S(q,t) « exp(-(ra⁽⁰⁾t)^2/3). The initial decay rate rq⁽⁰' exhibits a power law of the form rq⁽⁰⁾. a 2.760.1 cnnfilaments thus approximate the universal behavior predicted for a Rouse-Zimm chain by Dubois-Violette and de Gennes (Physics 1967, 3, 181). The deviation from the predicted q³dependence of the initial decay rate is similar to that found for synthetic polymers by several groups. Concentration-dependent deviations from Rouse-Zimm behavior, which are most prominent for rq⁽⁰⁾£ » 1, are attributed to filament interactions. Translational diffusion coefficients of fully polymerized actin filaments were measured by fluorescence photobleaching (FRAP). We obtained a diffusion coefficient of Dtran8,----- 8 x 10^-11cm²/s for ca= 1 mg/mL. Da scaled roughly like D

Duke Scholars

Author Christoph F. Schmidt Physics