ATP hydrolysis stimulates large length fluctuations in single actin filaments

TL;DR

This paper presents a theoretical model showing how ATP hydrolysis influences length fluctuations in single actin filaments, revealing different dynamic regimes and comparing hydrolysis mechanisms.

Contribution

The study introduces an exact analytical model for actin filament dynamics that incorporates ATP hydrolysis, filament tip geometry, and monomer interactions, providing new insights into filament length fluctuations.

Findings

ATP hydrolysis significantly affects filament dynamics.

Length fluctuations peak at the boundary between dynamic regimes.

Both random and vectorial hydrolysis mechanisms yield similar qualitative results.

Abstract

Polymerization dynamics of single actin filaments is investigated theoretically using a stochastic model that takes into account the hydrolysis of ATP-actin subunits, the geometry of actin filament tips, the lateral interactions between the monomers as well as the processes at both ends of the polymer. Exact analytical expressions are obtained for a mean growth velocity and for dispersion in length fluctuations. It is found that the ATP hydrolysis has a strong effect on dynamic properties of single actin filaments. At high concentrations of free actin monomers the mean size of unhydrolyzed ATP-cap is very large, and the dynamics is governed by association/dissociation of ATP-actin subunits. However, at low concentrations the size of the cap becomes finite, and the dissociation of ADP-actin subunits makes a significant contribution to overall dynamics. Actin filament length fluctuations reach the maximum at the boundary between two dynamic regimes, and this boundary is always larger than the critical concentration. Random and vectorial mechanisms of hydrolysis are compared, and it is found that they predict qualitatively similar dynamic properties. The possibility of attachment and detachment of oligomers is also discussed. Our theoretical approach is successfully applied to analyze the latest experiments on the growth and length fluctuations of individual actin filaments.