Treponema pallidum TroA is a periplasmic zinc-binding protein with a helical backbone

The crystal structure of recombinant TroA, a zinc-binding protein component of an ATP-binding cassette transport system in Treponema pallidum, was det ermined at a resolution of 1.8 Angstrom. The organization of the protein is largely similar to other periplasmic ligand-binding proteins (PLBP), in th at two independent globular domains interact with each other to create a zi nc-binding cleft between them. The structure has one bound zinc pentavalent ly coordinated to residues from both domains. Unlike previous PLBP structur es that have an interdomain hinge composed of beta-strands, the N- and C-do mains of TroA are linked by a single long backbone helix This unique backbo ne helical conformation was possibly adopted to limit the hinge motion asso ciated with ligand exchange.