ZnuA includes periplasmic solute binding proteins such as TroA that interacts with an ATP-binding cassette transport system in Treponema pallidum. ZnuA is part of the bacterial zinc-uptake complex ZnuABC, whose components are the following families, ZinT, pfam09223, pfam00950, pfam00005, all of which are regulated by the transcription-regulator family FUR, pfam01475. ZinT acts as a Zn2+-buffering protein that delivers Zn2+ to ZnuA (TroA), a high-affinity zinc-uptake protein. In Gram-negative bacteria the ZnuABC transporter system ensures an adequate import of zinc in Zn2+-poor environments, such as those encountered by pathogens within the infected host.