1.A.35.4.1
Zn²⁺/Cd²⁺ efflux system, ZntB. Mg²⁺ is not transported. Wan et al. 2011 reported crystal structures in dimeric and physiologically relevant homopentameric forms at 2.3 Å and 3.1 Å resolutions, respectively. The funnel-like structure is similar to that of the homologous Thermotoga maritima CorA Mg²⁺ channel and a Vibrio parahaemolyticus ZntB (VpZntB). However, the central α7 helix forming the inner wall of the StZntB funnel is oriented perpendicular to the membrane instead of the marked angle seen in CorA or VpZntB. Consequently, the StZntB funnel pore is cylindrical, not tapered, which may represent an "open" form of the ZntB soluble domain. There are three Zn²⁺ binding sites in the full-length ZntB, two of which could be involved in Zn²⁺ transport.