Oxo-iron clusters in a bacterial iron-trafficking protein: new roles for a conserved motif

We report a set of three 1.8–1.9 Å resolution X-ray crystal structures of Neisseria gonorrhoeae Fbp (ferric-ion binding protein): (i) open-cleft apo-Fbp containing bound phosphate, (ii) opencleft mono-Fe Fbp capped by nitrilotriacetate, and (iii) open-cleft trinuclear oxo-iron Fbp, the first structure of an iron-cluster adduct of a transferrin. The nine independent molecules in the unit cells provide ‘snapshots’ of the versatile dynamic structural roles of the conserved dityrosyl iron-binding motif (Tyr195-Tyr196) which control the capture and, possibly, processing of iron. These findings have implications for understanding bacterial iron acquisition and dissimilation, and organic/mineral interfaces. Key words: bacterial transferrin, dityrosyl motif, iron-binding protein, iron transport, oxo-iron cluster, X-ray crystallography