FIGURE 2.

Extracellular copper-binding molecules. a, ceruloplasmin has six copper-binding sites of which three are type I copper centers coordinated with two histidine residues, a cysteine residue and a methionine residue (48). b, methanobactin structures contain a recognizable peptide backbone with distinctive oxazolone heterocycles, which are implicated in copper ion coordination (43). c, yersiniabactin has three heterocyclic nitrogens (two thiazoline and one thiazolidine) that contribute to a square planar configuration around Cu(II) alongside the phenolate oxygen (61).