Fluorescence Correlation Spectroscopy analysis of segmental dynamics in Actin filaments

TL;DR

This paper adapts Fluorescence Correlation Spectroscopy to study the segmental dynamics of actin filaments, providing detailed measurements over a wide timescale and comparing results with theoretical models.

Contribution

It introduces a new FCS-based method to analyze semi-flexible polymer dynamics and validates it with experimental data on actin filaments.

Findings

FCS formalism successfully relates correlation functions to segment displacements.

Experimental data agree with hydrodynamic interaction theories.

Segmental MSD measured over five decades in time.

Abstract

We adapt Fluorescence Correlation spectroscopy (FCS) formalism to the studies of the dynamics of semi-flexible polymers and derive expressions relating FCS correlation function to the longitudinal and transverse mean square displacements of polymer segments. We use the derived expressions to measure the dynamics of actin filaments in two experimental situations: filaments labeled at distinct positions and homogeneously labeled filaments. Both approaches give consistent results and allow to measure the temporal dependence of the segmental mean-square displacement (MSD) over almost five decades in time, from ~0.04ms to 2s. These noninvasive measurements allow for a detailed quantitative comparison of the experimental data to the current theories of semi-flexible polymer dynamics. Good quantitative agreement is found between the experimental results and theories explicitly accounting for the hydrodynamic interactions between polymer segments.