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Modeling of the elongation and retraction of Escherichia coli P pili under strain by Monte Carlo simulations

Björnham, Oscar, 1976- (author)
Umeå universitet,Institutionen för tillämpad fysik och elektronik
Axner, Ove (author)
Umeå universitet,Institutionen för fysik
Andersson, Magnus (author)
Umeå universitet,Institutionen för fysik
 (creator_code:org_t)
2007-10-10
2008
English.
In: European Biophysics Journal. - : Springer Science and Business Media LLC. - 0175-7571 .- 1432-1017. ; 37:4, s. 381-391
  • Journal article (peer-reviewed)
Abstract Subject headings
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  • P pili are fimbrial adhesion organelles expressed by uropathogenic Escherichia coli in the upper urinary tract. They constitute a stiff helix-like polymer consisting of a number of subunits joined by head-to-tail bonds. The elongation and retraction properties of individual P pili exposed to strain have been modeled by Monte Carlo (MC) simulations. The simulation model is based upon a three-state energy landscape that deforms under an applied force. Bond opening and closure are modeled by Bells theory while the elongation of the linearized part of the pilus is described by a worm-like chain model. The simulations are compared with measurements made by force measuring optical tweezers. It was found that the simulations can reproduce pili elongation as well as retraction, under both equilibrium and dynamic conditions, including entropic effects. It is shown that the simulations allow for an assessment of various model parameters, e.g. the unfolding force, energy barrier heights, and various distances in the energy landscape, including their stochastic spread that analytical models are unable to do. The results demonstrate that MC simulations are useful to model elongation and retraction properties of P pili, and therefore presumably also other types of pili, exposed to strain and/or stress. MC simulations are particularly suited for description of helix-like pili since these have an intricate self-regulating mechanical elongation behavior that makes analytical descriptions non-trivial when dynamic processes are studied, or if additional interactions in the rod or the behavior of the adhesion tip needs to be modeled.

Keyword

P pili
Escherichia coli
Optical tweezers
Monte Carlo simulations
Unfolding
Force spectroscopy

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