The unfolding of the P pili quaternary structure by stretching is reversible, not plastic - PubMed (original) (raw)

The unfolding of the P pili quaternary structure by stretching is reversible, not plastic

Erik Fällman et al. EMBO Rep. 2005 Jan.

Abstract

P pili are protein filaments expressed by uropathogenic Escherichia coli that mediate binding to glycolipids on epithelial cell surfaces, which is a prerequisite for bacterial infection. When a bacterium, attached to a cell surface, is exposed to external forces, the pili, which are composed of approximately 10(3) PapA protein subunits arranged in a helical conformation, can elongate by unfolding to a linear conformation. This property is considered important for the ability of a bacterium to withstand shear forces caused by urine flow. It has hitherto been assumed that this elongation is plastic, thus constituting a permanent conformational deformation. We demonstrate, using optical tweezers, that this is not the case; the unfolding of the helical structure to a linear conformation is fully reversible. It is surmised that this reversibility helps the bacteria regain close contact to the host cells after exposure to significant shear forces, which is believed to facilitate their colonization.

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Figures

Figure 1

Figure 1

Schematic illustration of a P pilus in its unstretched native form (A) as well as in three different elongation regions (I–III; B–D). A P pilus consists of a PapA rod (6.8 nm in diameter) arranged in a helix (Gong & Makowski, 1992) that is anchored to a bacterial membrane by PapH (Båga et al, 1987) and connected to a fibrillum by a PapK adaptor (Jacob-Dubuisson et al, 1993). The fibrillum tip (15 nm long and 2–3 nm in diameter; Bullitt & Makowski, 1998) is a flexible structure composed of PapE (Lindberg et al, 1986), PapF (Lindberg et al, 1986) and the PapG (Lindberg et al, 1987; Kuehn et al, 1992; Jacob-Dubuisson et al, 1993) adhesin. The forces from the adjacent-turn and the head-to-tail interactions are indicated.

Figure 2

Figure 2

Elongation and contraction study of P pili. Two consecutive elongation and contraction cycles are shown, displayed by the blue and black curves in (A) and by the red and green curves in (B), respectively. The numbers in the graphs indicate important bacterium-to-bead distances. The regions of the remaining pilus during contraction are indicated (I, II or III). The unfolding and folding forces are indicated with arrows.

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References

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