UCS Protein Rng3p Is Essential for Myosin-II Motor Activity during Cytokinesis in Fission Yeast

Benjamin C Stark,Luther W Pollard,Matthew Lord,Michael L James,Vladimir Sirotkin,Takashi Toda

doi:10.1371/journal.pone.0079593

Benjamin C Stark, Luther W Pollard + Show 4 more

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https://doi.org/10.1371/journal.pone.0079593

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Journal: PloS one	Publication Date: Nov 14, 2013
Citations: 21	License type: CC BY 4.0

Affiliation: University of Vermont, SUNY Upstate Medical University

Abstract

UCS proteins have been proposed to operate as co-chaperones that work with Hsp90 in the de novo folding of myosin motors. The fission yeast UCS protein Rng3p is essential for actomyosin ring assembly and cytokinesis. Here we investigated the role of Rng3p in fission yeast myosin-II (Myo2p) motor activity. Myo2p isolated from an arrested rng3-65 mutant was capable of binding actin, yet lacked stability and activity based on its expression levels and inactivity in ATPase and actin filament gliding assays. Myo2p isolated from a myo2-E1 mutant (a mutant hyper-sensitive to perturbation of Rng3p function) showed similar behavior in the same assays and exhibited an altered motor conformation based on limited proteolysis experiments. We propose that Rng3p is not required for the folding of motors per se, but instead works to ensure the activity of intrinsically unstable myosin-II motors. Rng3p is specific to conventional myosin-II and the actomyosin ring, and is not required for unconventional myosin motor function at other actin structures. However, artificial destabilization of myosin-I motors at endocytic actin patches (using a myo1-E1 mutant) led to recruitment of Rng3p to patches. Thus, while Rng3p is specific to myosin-II, UCS proteins are adaptable and can respond to changes in the stability of other myosin motors.

Highlights

Unc-45/Cro1/She4 (UCS) proteins are a family of myosin motor regulators that are conserved across eukaryotes [1]
UCS proteins are conserved throughout eukaryotes and have been proposed to act as co-chaperones that work with Hsp90 during the de novo folding of myosin motor domains
In this study we investigated the mode of action of the fission yeast UCS protein, Rng3p

Summary

Introduction

Unc-45/Cro1/She (UCS) proteins are a family of myosin motor regulators that are conserved across eukaryotes [1]. UCS proteins typically contain a C-terminal UCS domain that binds myosin motors, a variable central domain that may play a role in oligomerization [2], and an N-terminal tetratricopeptide repeat (TPR) domain that interacts with the Hsp chaperone (Figure 1) [3]. Interaction between the UCS protein and Hsp has been shown to be important for the latter stages of the de novo folding of muscle myosin-II motors [4,5]. The UCS protein may act as a co-chaperone that accelerates motor folding by bringing motors bound at the UCS domain into close contact with Hsp bound by the TPR domain [1,2,4]. Defects in UCS protein function have been associated with various diseases including arteriovenous malformation, cardiomyopathy, and cancer [6,7,8,9]. Similar defects are seen when UCS protein function is attenuated in zebrafish and Drosophila [9,12,13,14]

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