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Biophys. J. BioFAST: First Published September 1, 2006. doi:10.1529/biophysj.106.088989
© 2006 by the Biophysical Society.

A more recent version of this article appeared on November 15, 2006.
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PROTEINS

The Mechanical Properties of E. coli Type 1 Pili Measured by Atomic Force Microscopy Techniques

Eric Miller 1, Tzintzuni I Garcia 2, Scott Hultgren 1 and Andres Oberhauser 2*

1 Washington University School of Medicine
2 University of Texas Medical Branch

* To whom correspondence should be addressed. E-mail: afoberha{at}utmb.edu.

Submitted on May 16, 2006
Revised on August 7, 2006
Accepted on 16 August 2006


  Abstract
The first step in the encounter between a host and pathogen is attachment to the host epithelium. For uropathogenic Escherichia coli, these interactions are mediated by type 1 and P- adhesive pili which are long (~1µm) rods composed of more than 1000 protein subunits arranged in a helical structure. Here we used single-molecule atomic force microscopy to study the mechanical properties of type 1 pili. We found that type 1 pili readily extend under an applied force and that this extensibility is the result of unwinding the pilus rod's helical quaternary structure. The forced unraveling is also reversible, with helical rewinding taking place under considerable forces (~60pN). These data are similar to those obtained on P-pili using optical tweezers, indicating that these are conserved properties of uropathogenic E. coli pili. We also show that our data can be readily reproduced by using Monte-Carlo simulation techniques based on a two-state kinetic model. This model provides a simple way to extrapolate the mechanical behavior of pili under a wide range of forces. We propose that type 1 pilus unraveling is an essential mechanism for absorbing physiological shear forces encountered during urinary tract infections and probably essential for adhesion and colonization of the bladder epithelium.

Key Words: atomic force microscopy, force spectroscopy, pili, protein elasticity, protein nanomechanics, single-molecule




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Copyright © 2006 by the Biophysical Society.