Molecular structure study on the polyelectrolyte properties of actin filaments

Measurement and Characterization of the Electrical Properties of Actin Filaments

Actin filaments, as key components of the cytoskeleton, have aroused great interest due to their numerous functional roles in eukaryotic cells, including intracellular electrical signaling. The aim of this research is to characterize the alternating current (AC) conduction characteristics of both globular and polymerized actin and quantitatively compare their values to those theoretically predicted earlier. Actin filaments have been demonstrated to act as conducting bionanowires, forming a signaling network capable of transmitting ionic waves in cells. We performed conductivity measurements for different concentrations of actin, considering both unpolymerized and polymerized actin to identify potential differences in their electrical properties. These measurements revealed two relevant characteristics: first, the polymerized actin, arranged in filaments, has a lower impedance than its globular counterpart; second, an increase in the actin concentration leads to higher conductivities. Furthermore, from the data collected, we developed a quantitative model to represent the electrical properties of actin in a buffer solution. We hypothesize that actin filaments can be modeled as electrical resistor-inductor-capacitor (RLC) circuits, where the resistive contribution is due to the viscous ion flows along the filaments; the inductive contribution is due to the solenoidal flows along and around the helix-shaped filament and the capacitive contribution is due to the counterion layer formed around each negatively charged filament.

CACPPAF, a COMSOL application to characterize polyelectrolyte properties of actin filaments

We present an interactive COMSOL web application that allows both expert and non-expert users to numerically evaluate the electric potential, ionic concentration distribution, velocity profile, and ionic current along a molecular structure surface characterizing actin filaments. This online computational and visualization tool runs on a high performance server (http://marucholab.physics.utsa.edu:2036), that enables users to perform multiple analyses and comparisons without compromising computational resources. As a unique feature, the multiphysics formulation accounts for the filament surface roughness, the finite filament size, and the ionic condensation, providing a deeper understanding of the electrochemical phenomena taking place at the interface between the irregular charged shape of the filament and its biological environment. Overall, the interactive component allows investigators to characterize polyelectrolyte properties of healthy and abnormal actin filaments in physiological and pathological conditions.