Side-binding proteins modulate actin filament dynamics.

Alvaro H Crevenna,Kaja Kowalska,Marcelino Arciniega,Don C Lamb,Aurélie Dupont,Roland Wedlich-Söldner,Naoko Mizuno,Oliver F Lange

doi:10.7554/elife.04599

Abstract

Actin filament dynamics govern many key physiological processes from cell motility to tissue morphogenesis. A central feature of actin dynamics is the capacity of filaments to polymerize and depolymerize at their ends in response to cellular conditions. It is currently thought that filament kinetics can be described by a single rate constant for each end. In this study, using direct visualization of single actin filament elongation, we show that actin polymerization kinetics at both filament ends are strongly influenced by the binding of proteins to the lateral filament surface. We also show that the pointed-end has a non-elongating state that dominates the observed filament kinetic asymmetry. Estimates of flexibility as well as effects on fragmentation and growth suggest that the observed kinetic diversity arises from structural alteration. Tuning elongation kinetics by exploiting the malleability of the filament structure may be a ubiquitous mechanism to generate a rich variety of cellular actin dynamics.

Highlights

Central cellular processes such as cell migration, cytokinesis, endocytosis, and mechanosensation depend critically on actin-based force generation and actin filament turnover (Pollard and Borisy, 2003; Lecuit et al, 2011)
Labeled actin was used to visualize the growth of actin filaments (Figure 1A–B) using total internal reflection fluorescence (TIRF) microscopy
We have shown that asymmetry in filament elongation is a consequence of a non-elongating state at the pointed-end and that the general versatility of actin dynamics may be a response to the binding of various proteins

Summary

Introduction

Central cellular processes such as cell migration, cytokinesis, endocytosis, and mechanosensation depend critically on actin-based force generation and actin filament turnover (Pollard and Borisy, 2003; Lecuit et al, 2011). The molecular basis of actin filament turnover derives from the association and dissociation of monomers from each filament end and depends on the nucleotide (ATP, ADP · Pi, or ADP) bound to the actin monomer (Pollard, 1986). The filament is kinetically asymmetric, where one end (called the barbed-end) is observed to grow an order of magnitude faster than the other end (the pointed-end) (Pollard, 1986). The critical concentration for polymerization is different for the two ends. The origin of the asymmetry is not fully understood.

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Conclusion