Abstract

Uropathogenic Escherichia coli invades and colonizes hosts by attaching to cells using adhesive pili on the bacterial surface. Although many biophysical techniques have been used to study the structure and mechanical properties of pili, many important details are still unknown. Here we use proton-detected solid-state NMR experiments to investigate solvent accessibility and structural dynamics. Deuterium back-exchange at labile sites of the perdeuterated, fully proton back-exchanged pili was conducted to investigate hydrogen/deuterium (H/D) exchange patterns of backbone amide protons in pre-assembled pili. We found distinct H/D exchange patterns in lateral and axial intermolecular interfaces in pili. Amide protons protected from H/D exchange in pili are mainly located in the core region of the monomeric subunit and in the lateral intermolecular interface, whereas the axial intermolecular interface and the exterior region of pili are highly exposed to H/D exchange. Additionally, we performed molecular dynamics simulations of the type 1 pilus rod and estimated the probability of H/D exchange based on hydrogen bond dynamics. The comparison of the experimental observables and simulation data provides insights into stability and mechanical properties of pili.

Highlights

  • Uropathogenic Escherichia coli (UPEC) is the primary pathogen causing urinary tract infections by adhesion to the surface of host bladder epithelial cells (Martinez et al 2000)

  • We assume that the peak splittings and the peak broadenings are related to conformational heterogeneity and/or slow conformational dynamics

  • The chemical shift perturbations (CSPs) of backbone amide 1HN and 15N resonances, calculated from chemical shifts of self-complemented monomeric FimA (FimAa, solution NMR) (Puorger et al 2011) and polymerized FimA, indicate which residues are involved in intermolecular interactions resulting from polymerization (Fig. S2)

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Summary

Introduction

Uropathogenic Escherichia coli (UPEC) is the primary pathogen causing urinary tract infections by adhesion to the surface of host bladder epithelial cells (Martinez et al 2000). The pilus rod subunit FimA has an incomplete immunoglobulin-like β-sheet fold (pilin body) and is complemented by a protruding N-terminal extension (Nte, termed donor strand) of a neighboring subunit with non-covalent interactions (Choudhury et al 1999). This donor strand complementation (DSC) is processed by the highly conserved chaperone-usher pathway in the periplasmic space of UPEC with assistance of the chaperone FimC and the usher FimD (Phan et al 2011; Geibel et al 2013).

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