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Uncharacterized bacterial subgroup of the Salmonella typhimurium Zn2+ transporter ZntB-like subfamily The MIT superfamily of essential membrane proteins is involved in transporting divalent cations (uptake or efflux) across membranes. The ZntB-like subfamily includes the Zn2+ transporter Salmonella typhimurium ZntB which mediates the efflux of Zn2+ (and Cd2+). Structures of the intracellular domain of Vibrio parahaemolyticus and Salmonella typhimurium ZntB form funnel-shaped homopentamers, the tip of the funnel is formed from two C-terminal transmembrane (TM) helices from each monomer, and the large opening of the funnel from the N-terminal cytoplasmic domains. The GMN signature motif of the MIT superfamily occurs just after TM1, mutation within this motif is known to abolish Mg2+ transport through Salmonella typhimurium CorA, and Mrs2p. Natural variants such as GVN and GIN which occur in proteins belonging to this subfamily, may be associated with the transport of different divalent cations, such as zinc and cadmium. The functional diversity of MIT transporters may also be due to minor structural differences regulating gating, substrate selection, and transport. |
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