Intrinsic Capability of Budding Yeast Cofilin to Promote Turnover of Tropomyosin-Bound Actin Filaments

Xiaoxue Fan,Skylar Martin-Brown,Rong Li,Laurence Florens,Edathara Abraham

doi:10.1371/journal.pone.0003641

Abstract

The ability of actin filaments to function in cell morphogenesis and motility is closely coupled to their dynamic properties. Yeast cells contain two prominent actin structures, cables and patches, both of which are rapidly assembled and disassembled. Although genetic studies have shown that rapid actin turnover in patches and cables depends on cofilin, how cofilin might control cable disassembly remains unclear, because tropomyosin, a component of actin cables, is thought to protect actin filaments against the depolymerizing activity of ADF/cofilin. We have identified cofilin as a yeast tropomyosin (Tpm1) binding protein through Tpm1 affinity column and mass spectrometry. Using a variety of assays, we show that yeast cofilin can efficiently depolymerize and sever yeast actin filaments decorated with either Tpm1 or mouse tropomyosins TM1 and TM4. Our results suggest that yeast cofilin has the intrinsic ability to promote actin cable turnover, and that the severing activity may rely on its ability to bind Tpm1.

Highlights

The ability to assemble distinct and dynamic actin structures in the same cell is critical for the diverse role of actin in cell motility and morphogenesis [1]
The rapid turnover of actin patches has been shown to depend on cofilin [4], and a recent study found that cofilin was not detected along actin cables under normal conditions, rapid turnover of actin cables requires cofilin [5]
Tropomyosin-containing actin structures carry out many important functions such as cellular contractility, motility and polarized transport [18]

Summary

Introduction

The ability to assemble distinct and dynamic actin structures in the same cell is critical for the diverse role of actin in cell motility and morphogenesis [1]. In yeast cells that undergo polarized growth, actin cables and patches are dynamically assembled near growth sites and are required for two different cellular functions: polarized transport and endocytosis, respectively [2]. Cofilin is a member of the ADF/cofilin family of low molecular weight actin-binding proteins. These proteins can bind to actin monomers (G-actin) and filaments and stimulate depolymerization and fragmentation of F-actin [12]. Every eukaryotic cell type examined to-date contains at least one member of the ADF/cofilin family, suggesting that cofilin performs a universally important function. Cofilin-mediated F-actin severing and turnover are thought to be critical for rapid remodeling of actin organization in response to external stimuli, and for recycling of G-actin to sustain actin polymerization during cellular or intra cellular motility processes [13]

Methods

Results

Conclusion