BIOPHYSICAL THEORY AND MODELING |
The biomechanical properties of E. coli pili for urinary tract attachment reflect the host environment
Magnus Andersson 1, Bernt Eric Uhlin 2 and Erik G Fällman 3*
1 Department of physics
2 Department of molecular biology
3 Department of Physics
* To whom correspondence should be addressed. E-mail: erik.fallman{at}physics.umu.se.
Submitted on April 12, 2007
Revised on June 13, 2007
Accepted on 27 June 2007
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Abstract |
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Uropathogenic Escherichia coli express pili that mediate binding to host tissue cells. We demonstrate with in situ force measuring optical tweezers that the ability of P and type 1 pili to elongate by unfolding under exposure to stress is a shared property with some differences. The unfolding force of the quaternary structures under equilibrium conditions is similar, 28 ± 2 and 30 ± 2 pN for P pili and type 1 pili, respectively. However, type 1 pili are found to be more rigid than P pili through their stronger layer-to-layer bonds. It was found that type 1 pili enter a dynamic regime at elongation speeds of 6 nm/s, compared to 400 nm/s for P pili, i.e. it responds faster to an external force. This possibly helps type 1 to withstand the irregular urine flow in the urethra as compared to the more constant urine flow in the upper urinary tract. Also, it was found that type 1 pili refold during retraction at two different levels which possibly could be related to several possible configurations. Our findings highlight functions that are believed to be of importance for the bacterial ability to sustain a basic anti-microbial mechanism of the host and for bacterial colonization.
Key Words:
P pili, bond breaking, optical tweezers, type 1 pili, unfolding, uropathogenic Escherichia coli
