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Biophys. J. BioFAST: First Published October 28, 2005. doi:10.1529/biophysj.105.061010
© 2005 by the Biophysical Society.

A more recent version of this article appeared on January 15, 2006.
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Measuring Molecular Elasticity by Atomic Force Microscope Cantilever Fluctuations

Bryan T Marshall 1, Krishna K. Sarangapani 2, Jianhua Wu 3, Michael B Lawrence 4, Rodger P McEver 5 and Cheng Zhu 2*

1 Aderans Research Institute
2 Georgia Institute of Technology
3 Sun Yat-Sen University
4 University of Virginia
5 Oklahoma Medical Research Foundation

* To whom correspondence should be addressed. E-mail: cheng.zhu{at}me.gatech.edu.

Submitted on February 8, 2005
Revised on April 13, 2005
Accepted on 4 October 2005


  Abstract
In single molecule mechanics experiment the molecular elasticity is usually measured from the deformation in response to a controlled applied force, e.g., via an atomic force microscope cantilever. Here we describe an alternative method based on a recently developed theory (J. Biomech. Eng., 2005). The concept is to measure the change in thermal fluctuations of the cantilever tip with and without its coupling to a rigid surface via the molecule. The validity and accuracy of this new method was demonstrated by its application to the elasticity measurements of L- and P-selectin complexed with P-selectin glycoprotein ligand-1 or their respective antibodies, which showed comparable values with those measured by the conventional method. L- and P-selectin were found to behave as nearly linear springs capable of sustaining large forces and strains without sudden unfolding. The measured spring constants of ~~4 and ~~1 pN/nm for L - and P-selectin, respectively, suggest that a physiological force of ~~100 pN would result in a ~~200% strain for the respective selectins.

Key Words: AFM, molecular elasticity, selectins, thermal fluctuations




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Copyright © 2005 by the Biophysical Society.