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Biophys. J. BioFAST: First Published December 16, 2005. doi:10.1529/biophysj.105.074674
© 2005 by the Biophysical Society.

A more recent version of this article appeared on March 1, 2006.
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BIOPHYSICAL THEORY AND MODELING

A Sticky Chain Model of the Elongation and Unfolding of Escherichia Coli P Pili under Stress

Magnus Andersson 1, Erik Fällman 1, Bernt Eric Uhlin 2 and Ove Axner 1*

1 Department of Physics, Umeå University, S-901 87 Umeå, Sweden
2 Department of Molecular biology, Umeå University, S-901 87 Umeå, Sweden

* To whom correspondence should be addressed. E-mail: ove.axner{at}physics.umu.se.

Submitted on September 16, 2005
Revised on November 7, 2005
Accepted on 15 November 2005


  Abstract
A model of the elongation of P pili expressed by uropathogenic Escherichia coli exposed to stress is presented. The model is based upon the sticky chain concept, which is based upon Hooke's law for elongation of the layer-to-layer and head-to-tail bonds between neighboring units in the PapA rod and a kinetic description of the opening and closing of bonds, described by rate equations and an energy landscape model. It provides an accurate description of the elongation behavior of P pili under stress and supports a hypothesis that the PapA rod shows all three basic stereotypes of elongation/unfolding; elongation of bonds in parallel, the zipper mode of unfolding, and elongation and unfolding of bonds in series. The two first elongation regions are dominated by a cooperative bond-opening, in which each bond is influenced by its neighbor, whereas the third region can be described by individual bond-opening, in which the bonds open and close randomly. A methodology for a swift extraction of model parameters from force-vs.-elongation measurements performed under equilibrium conditions is derived. Entities such as the free energy, the stiffness, the elastic elongation, the opening length of the various bonds, and the number of PapA units in the rod are determined.

Key Words: Bond breaking, Energy landscape, Helical structure, Optical tweezers, PapA rod, Uropathogenic Escherichia coli




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Copyright © 2005 by the Biophysical Society.