title: Biomechanical and structural features of CS2 fimbriae of enterotoxigenic Escherichia coli.
abstract: Enterotoxigenic Escherichia coli (ETEC) are a major cause of diarrhea worldwide, and infection of children in under-developed countries often leads to high mortality rates. Isolated ETEC expresses a plethora of colonization factors (fimbriae/pili), of which CFA/I and CFA/II, which are assembled via the alternate chaperone pathway (ACP), are among the most common. Fimbriae are filamentous structures whose shafts are primarily composed of helically arranged single pilin-protein subunits, with a unique biomechanical ability to unwind and rewind. A sustained ETEC infection, under adverse conditions of dynamic shear forces, is primarily attributed to this biomechanical feature of ETEC fimbriae. Recent understanding about the role of fimbriae as virulence factors points to an evolutionary adaptation of their structural and biomechanical features. In this work, we investigated the biophysical properties of CS2 fimbriae from the CFA/II group. Homology modeling of its major structural subunit, CotA, reveals structural clues related to the niche in which they are expressed. Using optical-tweezers force spectroscopy, we found that CS2 fimbriae unwind at a constant force of 10 pN and have a corner velocity (i.e., the velocity at which the force required for unwinding rises exponentially with increased speed) of 1300 nm/s. The biophysical properties of CS2 fimbriae assessed in this work classify them into a low-force unwinding group of fimbriae together with the CFA/I and CS20 fimbriae expressed by ETEC strains. The three fimbriae are expressed by ETEC, colonize in similar gut environments, and exhibit similar biophysical features, but differ in their biogenesis. Our observation suggests that the environment has a strong impact on the biophysical characteristics of fimbriae expressed by ETEC.
authors.affiliation: Department of Physics, Umeå University, Umeå, Sweden.
authors.forename: Narges
authors.initials: N
authors.lastname: Mortezaei
authors.affiliation: Department of Physics, Umeå University, Umeå, Sweden; Umeå Centre for Microbial Research (UCMR), Umeå University, Umeå, Sweden.
authors.forename: Bhupender
authors.initials: B
authors.lastname: Singh
authors.affiliation: Department of Physics, Umeå University, Umeå, Sweden.
authors.forename: Johan
authors.initials: J
authors.lastname: Zakrisson
authors.affiliation: Department of Physiology and Biophysics, Boston University School of Medicine, Boston, Massachusetts.
authors.forename: Esther
authors.initials: E
authors.lastname: Bullitt
authors.affiliation: Department of Physics, Umeå University, Umeå, Sweden; Umeå Centre for Microbial Research (UCMR), Umeå University, Umeå, Sweden. Electronic address: magnus.andersson@physics.umu.se.
authors.forename: Magnus
authors.initials: M
authors.lastname: Andersson
mesh_terms: D001426:Bacterial Proteins / Q000378:metabolism; D054307:Enterotoxigenic Escherichia coli / Q000502:physiology*; D010861:Fimbriae, Bacterial / Q000502:physiology*; D055595:Mechanical Phenomena; D018625:Microscopy, Atomic Force; D008958:Models, Molecular; D052898:Optical Tweezers; D013057:Spectrum Analysis
chemical_list: D001426:Bacterial Proteins