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. Author manuscript; available in PMC: 2018 Apr 1.
Published in final edited form as: Curr Opin Chem Biol. 2016 Dec 18;37:10–18. doi: 10.1016/j.cbpa.2016.09.012

Figure 4.

Figure 4

Cartoon depicting two models for how the host and E. coli compete for iron that involve enterobactin (Ent) and lipocalin-2 (LCN2). Canonical model: LCN2 sequesters Fe(III)-Ent in the extracellular space and thereby prevents Fe uptake by E. coli. Alternative model based on studies in human urine: LCN2 binds aryl metabolites present in urine and sequesters Fe(III). Metallation of Ent contributes to the demetallation of LCN2. Ent may prevent Fe(III) from binding to LCN2 and/or sequester Fe(III) from the Fe(III)-catechol-LCN2 complex, and the resulting Fe(III)-Ent provides nutrient iron to E. coli. Iron-bound LCN2 might be transported into host cells by receptor-mediated uptake. Abbreviations: CM, cell membrane; OM, outer membrane; IM, inner membrane.