Dynamic force spectroscopy of E. coli P pili
Magnus Andersson 1, Erik Fällman 1, Bernt Eric Uhlin 2 and Ove Axner 1*
1 Department of Physics, Umeå University, S-901 87 Umeå, Sweden
2 Department of Molecular biology, Umeå University, S-901 87 Umeå, Sweden
* To whom correspondence should be addressed. E-mail: ove.axner{at}physics.umu.se.
Submitted on April 18, 2006
Revised on May 22, 2006
Accepted on 21 June 2006
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Abstract |
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Surface organelles (so-called pili) expressed on the bacterial membrane mediate the adhesion of E. 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 helical-like 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.
Key Words:
Bond breaking, Energy landscape, Helical structure, Optical tweezers, PapA rod, Uropathogenic Escherichia coli
