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Biophys. J. BioFAST: First Published May 18, 2007. doi:10.1529/biophysj.107.106153
© 2007 by the Biophysical Society.

A more recent version of this article appeared on September 15, 2007.
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MUSCLE AND CONTRACTILITY

INTERACTION FORCES BETWEEN F-ACTIN AND TITIN PEVK DOMAIN MEASURED WITH OPTICAL TWEEZERS

Pasquale Bianco 1, Attila Nagy 1, András Kengyel 1, Dávid Szatmári 1, Zsolt Mártonfalvi 1, Tamás Huber 1 and Miklós SZ Kellermayer 1*

1 University of Pécs

* To whom correspondence should be addressed. E-mail: miklos.kellermayer.jr{at}aok.pte.hu.

Submitted on February 7, 2007
Revised on March 14, 2007
Accepted on 11 May 2007


  Abstract
Titin is a giant protein that determines the elasticity of striated muscle and is thought to play important role in numerous regulatory processes. Previous studies have shown that titin's PEVK domain interacts with F-actin, thereby creating viscous forces of unknown magnitude that may modulate muscle contraction. Here we measured, with optical tweezers, the forces necessary to dissociate F-actin from individual molecules of recombinant PEVK fragments rich either in polyE or PPAK motifs. Rupture forces at a stretch rate of 250 nm/s displayed wide, non-normal distribution, with a peak at ~8 pN in the case of both fragments. Dynamic force spectroscopy experiments revealed low spontaneous off-rates that were increased even by low forces. The loading-rate dependence of rupture force was biphasic for polyE in contrast with the monophasic response observed for PPAK. Analysis of the molecular lengths at which rupture occurred indicated that there are numerous actin-binding regions along the PEVK fragments' contour, suggesting that the PEVK domain is a promiscuous actin-binding partner. The complexity of PEVK-actin interaction points to an adaptable viscoelastic mechanism that safeguards sarcomeric structural integrity in the relaxed state and modulates thixotropic behavior during contraction.

Key Words: actin filament, bond lifetime, electrostatic interaction, laser tweezers, muscle thixotropy, recombinant protein fragments




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Copyright © 2007 by the Biophysical Society.