Elastic response, buckling and instability of microtubules under radial indentation

¹ Vrije Universiteit Amsterdam
² Universidad Autónoma de Madrid

^* To whom correspondence should be addressed. E-mail: iwanschaap{at}hotmail.com.

Submitted on November 16, 2005
Revised on March 2, 2006
Accepted on 12 May 2006

	Abstract

We have tested the mechanical properties of single microtubules by lateral indentation with the tip of an atomic force microscope. Indentations up to ~ 3.6 nm, i.e. 15 % of the microtubule diameter resulted in an approximately linear elastic response, and indentations were reversible without hysteresis. At an indentation force of around 0.3 nN we observed an instability corresponding to a ~ 1 nm indentation step in the taxol-stabilized microtubules, which could be due to partial or complete rupture of a relatively small number of lateral or axial tubulin-tubulin bonds. These indentations were reversible with hysteresis when the tip was retracted and no trace of damage was observed in subsequent high-resolution images. Higher forces caused substantial damage to the microtubules, which either led to depolymerization or, occasionally, to slowly reannealing holes in the microtubule wall. We have modeled the experimental results using finite element methods and find that the simple assumption of a homogeneous isotropic material, albeit structured with the characteristic protofilament corrugations, is sufficient to explain the linear elastic response of microtubules.

Key Words: Atomic Force Microscopy, Finite Element Modeling, Microtubule, Protein shells

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