Abstract
BilE has been reported as a bile resistance determinant that plays an important role in colonization of the gastrointestinal tract by Listeria monocytogenes, the causative agent of listeriosis. The mechanism(s) by which BilE mediates bile resistance are unknown. BilE shares significant sequence similarity with ATP-binding cassette (ABC) importers that contribute to virulence and stress responses by importing quaternary ammonium compounds that act as compatible solutes. Assays using related compounds have failed to demonstrate transport mediated by BilE. The putative substrate-binding domain (SBD) of BilE was expressed in isolation and the crystal structure solved at 1.5 Å. Although the overall fold is characteristic of SBDs, the binding site varies considerably relative to the well-characterized homologs ProX from Archaeoglobus fulgidus and OpuBC and OpuCC from Bacillus subtilis. This suggests that BilE may bind an as-yet unknown ligand. Elucidation of the natural substrate of BilE could reveal a novel bile resistance mechanism.
Highlights
Listeria monocytogenes is a Gram-positive bacterium that causes listeriosis, a potentially fatal disease which imposes a significant global burden [1]
The success of Listeria monocytogenes as a food-borne pathogen is aided by its ability to survive and grow in extreme conditions found both in food-preparation environments and in the gastrointestinal tract e.g., at low temperatures, at high salt concentrations, or in the presence of bile [4,5,6,7]
BilE is encoded by the genes lmo1421 and lmo1422 in a genetic arrangement similar to the OpuA
Summary
Listeria monocytogenes is a Gram-positive bacterium that causes listeriosis, a potentially fatal disease which imposes a significant global burden [1]. The success of Listeria monocytogenes as a food-borne pathogen is aided by its ability to survive and grow in extreme conditions found both in food-preparation environments and in the gastrointestinal tract e.g., at low temperatures (down to −0.4 ◦ C), at high salt concentrations (up to 10% w/v NaCl), or in the presence of bile [4,5,6,7]. Bile is a digestive secretion produced by the liver and stored and concentrated in the gallbladder before being released into the lower intestine, where it aids in the emulsification and solubilization of fats.
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