Direct measurement of conformational strain energy in protofilaments curling outward from disassembling microtubule tips

Abstract
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Abstract

Disassembling microtubules can generate movement independently of motor enzymes, especially at kinetochores where they drive chromosome motility. A popular explanation is the 'conformational wave' model, in which protofilaments pull on the kinetochore as they curl outward from a disassembling tip. But whether protofilaments can work efficiently via this spring-like mechanism has been unclear. By modifying a previous assay to use recombinant tubulin and feedback-controlled laser trapping, we directly demonstrate the spring-like elasticity of curling protofilaments. Measuring their mechanical work output suggests they carry ~25% of the energy of GTP hydrolysis as bending strain, enabling them to drive movement with efficiency similar to conventional motors. Surprisingly, a β-tubulin mutant that dramatically slows disassembly has no effect on work output, indicating an uncoupling of disassembly speed from protofilament strain. These results show the wave mechanism can make a major contribution to kinetochore motility and establish a direct approach for measuring tubulin mechano-chemistry.

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Jonathan W Driver

Department of Physiology and Biophysics, University of Washington, Seattle, United States

Competing interests
The authors declare that no competing interests exist.
Elisabeth A Geyer

Department of Biophysics and Biochemistry, University of Texas Southwestern Medical Center, Dallas, United States

Competing interests
The authors declare that no competing interests exist.
Megan E Bailey

Department of Physiology and Biophysics, University of Washington, Seattle, United States

Competing interests
The authors declare that no competing interests exist.
Luke M Rice

Department of Biophysics and Biochemistry, University of Texas Southwestern Medical Center, Dallas, United States

For correspondence
Luke.Rice@UTSouthwestern.edu

Competing interests
The authors declare that no competing interests exist.
Charles L Asbury

Department of Physiology and Biophysics, University of Washington, Seattle, United States

For correspondence
casbury@uw.edu

Competing interests
The authors declare that no competing interests exist.

"This ORCID iD identifies the author of this article:" 0000-0002-0143-5394

Funding

Sackler Scholars Program in Integrative Biophysics

Jonathan W Driver

Leukemia and Lymphoma Society

Jonathan W Driver

National Institutes of Health (T32CA080416)

Megan E Bailey

Packard Foundation (2006‐30521)

Charles L Asbury

NSF Graduate Research Fellowship (2014177758)

Elisabeth A Geyer

National Institutes of Health (RO1GM098543)

Luke M Rice

NSF Career Award (MCB1054947)

Luke M Rice

National Institutes of Health (RO1GM079373)

Charles L Asbury

The funders had no role in study design, data collection and interpretation, or the decision to submit the work for publication.

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This article is distributed under the terms of the Creative Commons Attribution License permitting unrestricted use and redistribution provided that the original author and source are credited.