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Biophys. J. BioFAST: First Published September 17, 2004. doi:10.1529/biophysj.104.044867
© 2004 by the Biophysical Society.

A more recent version of this article appeared on December 1, 2004.
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CELL BIOPHYSICS

Physical Properties of Escherichia coli P Pili Measured by Optical Tweezers

Jana Jass 1, Staffan Schedin 2, Erik Fällman 3, Jörgen Ohlsson 4, Ulf J Nilsson 4, Bernt Eric Uhlin 5 and Ove Axner 3*

1 Department of Microbiology and Immunology
2 Department of Applied Physics and Electronics
3 Department of Physics
4 Organic and Bioorganic Chemistry
5 Department of Molecular Biology

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

Submitted on April 23, 2004
Revised on May 26, 2004
Accepted on 14 September 2004


  Abstract
The mechanical behavior of individual P pili of uropathogenic Escherichia coli has been investigated using optical tweezers. P pili, whose main part constitutes the PapA rod, composed of ~103 PapA subunits in a helical arrangement, are distributed over the bacterial surface and mediate adhesion to host cells. They are particularly important in the pathogenesis of E. coli colonizing the upper urinary tract and kidneys. A biological model system has been established for in situ measurements of the forces that occur during mechanical stretching of pili. A mathematical model of the force-vs.-elongation behavior of an individual pilus has been developed. Three elongation regions of pili were identified. In region I, P pili stretch elastically, up to a relative elongation of 16 ±3%. The product of elasticity modulus and area of a P pilus, EA, was assessed to 154±20 pN (n=6). In region II, the quaternary structure of the PapA rod unfolds under a constant force of 272 pN (n{approx}100) by a sequential breaking of the interactions between adjacent layers of PapA subunits. This unfolding can elongate the pilus up to 7±2 times. In region III, pili elongate in a non-linear manner as a result of stretching, until the bond ruptures.

Key Words: Pap pili, PapA rod, helical structure, mechanical properties, unfolding, uropathogenic Escherichia coli




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Copyright © 2004 by the Biophysical Society.