Measurements and simulations of microtubule growth imply strong longitudinal interactions and reveal a role for GDP on the elongating end

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Abstract

Microtubule polymerization dynamics result from the biochemical interactions of αβ-tubulin with the polymer end, but a quantitative understanding has been challenging to establish. We used interference reflection microscopy to make improved measurements of microtubule growth rates and growth fluctuations in the presence and absence of GTP hydrolysis. In the absence of GTP hydrolysis, microtubules grew steadily with very low fluctuations. These data were best described by a computational model implementing slow assembly kinetics, such that the rate of microtubule elongation is primarily limited by the rate of αβ-tubulin associations. With GTPase present, microtubules displayed substantially larger growth fluctuations than expected based on the no GTPase measurements. Our modeling showed that these larger fluctuations occurred because exposure of GDP-tubulin on the microtubule end transiently 'poisoned' growth, yielding a wider range of growth rates compared to GTP only conditions. Our experiments and modeling point to slow association kinetics (strong longitudinal interactions), such that drugs and regulatory proteins that alter microtubule dynamics could do so by modulating either the association or dissociation rate of tubulin from the microtubule tip. By causing slower growth, exposure of GDP tubulin at the growing microtubule end may be an important early event determining catastrophe.

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Numerical data used to generate most of the figures have been provided as Source Data.

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Joseph M Cleary

Department of Biomedical Engineering, Pennsylvania State University, University Park, United States

Competing interests
The authors declare that no competing interests exist.
Tae Kim

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

Competing interests
The authors declare that no competing interests exist.
Annan SI Cook

Department of Biomedical Engineering, Pennsylvania State University, University Park, United States

Competing interests
The authors declare that no competing interests exist.
Lauren A McCormick

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

Competing interests
The authors declare that no competing interests exist.

"This ORCID iD identifies the author of this article:" 0000-0001-9164-0932
William O Hancock

Department of Biomedical Engineering, Pennsylvania State University, University Park, United States

For correspondence
woh1@psu.edu

Competing interests
The authors declare that no competing interests exist.

"This ORCID iD identifies the author of this article:" 0000-0001-5547-8755
Luke M Rice

Departments of Biophysics and Biochemistry, The 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.

"This ORCID iD identifies the author of this article:" 0000-0001-6551-3307

Funding

National Science Foundation (MCB-1615938)

Tae Kim
Lauren A McCormick
Luke M Rice

National Institutes of Health (R01-GM135565)

Lauren A McCormick
Luke M Rice

National Institutes of Health (R35-GM139568)

Joseph M Cleary
William O Hancock

National Institutes of Health (T32-GM108563)

Joseph M Cleary

National Institutes of Health (T32-GM008297)

Tae Kim

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.