FIG 7.

Model for tricompartmental copper ion detection in uropathogenic E. coli. The Cue and Cus systems maintain copper homeostasis in E. coli by sensing and responding to copper ions in the cytoplasm and periplasm, respectively. Data in this report are consistent with detection and response to extracellular copper ions using secreted yersiniabactin (Ybt) acting as both a soluble receptor and a copper-binding effector. The sensing pathway requires formation of stable Cu(II)-Ybt complexes, import through the outer membrane transporter, FyuA, and a YbtA-dependent signaling process that upregulates Ybt biosynthetic genes.