Crystal Structure of the Substrate-Binding Domain from Listeria monocytogenes Bile-Resistance Determinant BilE

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.

OpuF, a New Bacillus Compatible Solute ABC Transporter with a Substrate-Binding Protein Fused to the Transmembrane Domain

“…3). Although the BilEB SBP from L. monocytogenes apparently does not bind compatible solutes (97), the architecture of the ligand-binding site revealed through structural analysis nevertheless resembles that of the ProX, OpuBC, and OpuCC SBPs (Fig. 3).…”

“…The second hit on this list was the glycine betaine/ proline betaine-binding protein ProX (TM score: 0.93) from the hyperthermophilic archaeon Archaeoglobus fulgidus (95,96). Somewhat surprising was the top hit (TM score: 0.973) on the list, the BilE protein from Listeria monocytogenes (97). This is the substrate-binding domain of the BilEB TMD-SBP hybrid protein of the BilEA/BilEB ABC transporter, a resistance determinant against bile and a system that contributes to the colonization of the gastro-intestinal tract by the pathogen L. monocytogenes (98).…”

“…This is the substrate-binding domain of the BilEB TMD-SBP hybrid protein of the BilEA/BilEB ABC transporter, a resistance determinant against bile and a system that contributes to the colonization of the gastro-intestinal tract by the pathogen L. monocytogenes (98). Although it was initially suggested that BilE was involved in the uptake of osmostress protectants (glycine betaine, carnitine, and choline), subsequent studies showed that it does not serve this physiological function and instead is somehow involved in the exclusion of bile from the L. monocytogenes cell (97,98). We detected in our in silico-generated model of the SBP domain of the B. infantis OpuFB hybrid protein a putative ligand-binding site carrying an aromatic cage that is formed by the side chains of three tyrosine residues and of a phenylalanine (Fig.…”

Stability of ligand-induced protein conformation influences affinity in maltose-binding protein

“…The proteins are homologous to SBPs that are involved in the binding and transport of quaternary ammonium compounds (QACs). Based on crystal structures, both proteins possess a binding pocket that is very similar to that of other structurally characterized members of this family (47,48). Yet, the affinity of YehZ and BilE for QACs was at best a 1000-fold lower and no other ligands could be identified (48).…”

“…Regarding ABC-importer associated SBPs like MBP, several examples of proteins exists for which no ligand could be identified despite clear homology to proteins with known ligand specificity. Two examples are the SBPs YehZ from E. coli and BilE from L. monocytogenes (47,48). The proteins are homologous to SBPs that are involved in the binding and transport of quaternary ammonium compounds (QACs).…”