title: A structural basis for sustained bacterial adhesion: biomechanical properties of CFA/I pili.
abstract: Enterotoxigenic Escherichia coli (ETEC) are a major cause of diarrheal disease worldwide. Adhesion pili (or fimbriae), such as the CFA/I (colonization factor antigen I) organelles that enable ETEC to attach efficiently to the host intestinal tract epithelium, are critical virulence factors for initiation of infection. We characterized the intrinsic biomechanical properties and kinetics of individual CFA/I pili at the single-organelle level, demonstrating that weak external forces (7.5 pN) are sufficient to unwind the intact helical filament of this prototypical ETEC pilus and that it quickly regains its original structure when the force is removed. While the general relationship between exertion of force and an increase in the filament length for CFA/I pili associated with diarrheal disease is analogous to that of P pili and type 1 pili, associated with urinary tract and other infections, the biomechanical properties of these different pili differ in key quantitative details. Unique features of CFA/I pili, including the significantly lower force required for unwinding, the higher extension speed at which the pili enter a dynamic range of unwinding, and the appearance of sudden force drops during unwinding, can be attributed to morphological features of CFA/I pili including weak layer-to-layer interactions between subunits on adjacent turns of the helix and the approximately horizontal orientation of pilin subunits with respect to the filament axis. Our results indicate that ETEC CFA/I pili are flexible organelles optimized to withstand harsh motion without breaking, resulting in continued attachment to the intestinal epithelium by the pathogenic bacteria that express these pili.
authors.affiliation: Department of Physics, Umeå University, SE-901 87 Umeå, Sweden. magnus.andersson@physics.umu.se
authors.forename: Magnus
authors.initials: M
authors.lastname: Andersson
authors.forename: Oscar
authors.initials: O
authors.lastname: Björnham
authors.forename: Mats
authors.initials: M
authors.lastname: Svantesson
authors.forename: Arwa
authors.initials: A
authors.lastname: Badahdah
authors.forename: Bernt Eric
authors.initials: BE
authors.lastname: Uhlin
authors.forename: Esther
authors.initials: E
authors.lastname: Bullitt
mesh_terms: D018830:Adhesins, Escherichia coli / Q000502:physiology* / Q000648:ultrastructure; D001422:Bacterial Adhesion; D001696:Biomechanical Phenomena; D004926:Escherichia coli / Q000502:physiology / Q000648:ultrastructure; D036781:Fimbriae Proteins / Q000502:physiology* / Q000648:ultrastructure; D010861:Fimbriae, Bacterial / Q000502:physiology* / Q000648:ultrastructure; D017433:Protein Structure, Secondary
chemical_list: D018830:Adhesins, Escherichia coli; C022924:colonization factor antigens; D036781:Fimbriae Proteins