The association of myosin IB with actin waves in dictyostelium requires both the plasma membrane-binding site and actin-binding region in the myosin tail.

Hanna Brzeska,Kevin Pridham,Godefroy Chery,Margaret A Titus,Edward D Korn,Thierry Soldati

doi:10.1371/journal.pone.0094306

Hanna Brzeska, Kevin Pridham + Show 4 more

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https://doi.org/10.1371/journal.pone.0094306

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Abstract

F-actin structures and their distribution are important determinants of the dynamic shapes and functions of eukaryotic cells. Actin waves are F-actin formations that move along the ventral cell membrane driven by actin polymerization. Dictyostelium myosin IB is associated with actin waves but its role in the wave is unknown. Myosin IB is a monomeric, non-filamentous myosin with a globular head that binds to F-actin and has motor activity, and a non-helical tail comprising a basic region, a glycine-proline-glutamine-rich region and an SH3-domain. The basic region binds to acidic phospholipids in the plasma membrane through a short basic-hydrophobic site and the Gly-Pro-Gln region binds F-actin. In the current work we found that both the basic-hydrophobic site in the basic region and the Gly-Pro-Gln region of the tail are required for the association of myosin IB with actin waves. This is the first evidence that the Gly-Pro-Gln region is required for localization of myosin IB to a specific actin structure in situ. The head is not required for myosin IB association with actin waves but binding of the head to F-actin strengthens the association of myosin IB with waves and stabilizes waves. Neither the SH3-domain nor motor activity is required for association of myosin IB with actin waves. We conclude that myosin IB contributes to anchoring actin waves to the plasma membranes by binding of the basic-hydrophobic site to acidic phospholipids in the plasma membrane and binding of the Gly-Pro-Gln region to F-actin in the wave.

Highlights

Remodeling of the actin cytoskeleton plays an essential role in determining cell shape and movement [1]
Because of the relatively simple composition of Dictyostelium waves compared to mammalian cell waves and the numerous experimental advantages of Dictyostelium as a model system for cell motility, in the current study we focused on the interactions between Dictyostelium actin waves and myosin IB (MIB), the only myosin that has been shown to be associated with waves
What is the molecular basis of the association of myosin IB with the actin waves that self-propagate along the ventral surface of Dictyostelium? We found that two of the three known functional domains in the MIB tail are necessary and sufficient: the GPQ-region, which binds actin, and the BH-site, which binds to the plasma membrane

Summary

Introduction

Remodeling of the actin cytoskeleton plays an essential role in determining cell shape and movement [1]. Motile eukaryotic cells generate three-dimensional, self-organizing waves of F-actin which propagate along the ventral plasma membrane of cells adhering to a substrate. Identified initially in Dictyostelium by Vicker [2], actin waves were subsequently observed in BHK21 fibroblasts and mouse melanoma cells [3], neutrophils [4] and human osteosarcoma cells [5]. Actin waves in Dictyostelium have been described in considerable detail, principally by the Gerisch laboratory [6,7,8,9,10,11,12]. Because of the similarity in their composition (see below), it has been proposed that actin waves may function as planar potential phagocytic cup structures that scan a substrate surface in the search of particles to be phagocytosed [10,11]

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