May function as a periplasmic zinc chaperone or mediate direct transport of zinc from the periplasm to the cytoplasm under zinc-limited conditions. Binds zinc with high affinity, and can also bind cadmium, mercury or nickel. Preferentially binds Zn(2+) over Cd(2+). Contains one high affinity metal binding site, and can bind additional metal ions at other sites. Cytoplasmic in nonstressed cells, and exported to the periplasm upon exposure to cadmium. Repressed by Zur. Up-regulated in response to extreme Zn(2+) deprivation. Also induced by cadmium and hydrogen peroxide. Mutant shows a growth defect and a lowered cellular Zn(2+) level under Zn(2+) limitation. Mutant does not bind cadmium. Belongs to the calycin superfamily. ZinT family.