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Dynamic Force Spectroscopy of E. coli P Pili

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

^* Department of Physics and Department of Molecular Biology, Umeå University, Umeå, Sweden

Correspondence: Address reprint requests to Ove Axner, Dept. of Physics, Umeå University, SE-901 87 Umeå, Sweden. E-mail: ove.axner{at}physics.umu.se.

Surface organelles (so-called pili) expressed on the bacterial membrane mediate the adhesion of Escherichia coli causing urinary tract infection. These pili possess some extraordinary elongation properties that are assumed to allow a close bacterium-to-host contact even in the presence of shear forces caused by urine flow. The elongation properties of P pili have therefore been assessed for low elongation speeds (steady-state conditions). This work reports on the behavior of P pili probed by dynamic force spectroscopy. A kinetic model for the unfolding of a helixlike chain structure is derived and verified. It is shown that the unfolding of the quaternary structure of the PapA rod takes place at a constant force that is almost independent of elongation speed for slow elongations (up to 0.4 µm/s), whereas it shows a dynamic response with a logarithmic dependence for fast elongations. The results provide information about the energy landscape and reaction rates. The bond length and thermal bond opening and closure rates for the layer-to-layer bond have been assessed to 0.76 nm, 0.8 Hz, and 8 GHz, respectively. The results also support a previously constructed sticky-chain model for elongation of the PapA rod that until now had been experimentally verified only under steady-state conditions.

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				M. Andersson, B. E. Uhlin, and E. Fallman The Biomechanical Properties of E. coli Pili for Urinary Tract Attachment Reflect the Host Environment Biophys. J., November 1, 2007; 93(9): 3008 - 3014. [Abstract] [Full Text] [PDF]