metal ion transporter CorA-like divalent cation transporter superfamily
This superfamily of essential membrane proteins is involved in transporting divalent cations (uptake or efflux) across membranes. They are found in most bacteria and archaea, and in some eukaryotes. It is a functionally diverse group which includes the Mg2+ transporters of Escherichia coli and Salmonella typhimurium CorAs (which can also transport Co2+, and Ni2+ ), the CorA Co2+ transporter from the hyperthermophilic Thermotoga maritima, and the Zn2+ transporter Salmonella typhimurium ZntB, which mediates the efflux of Zn2+ (and Cd2+). It includes five Saccharomyces cerevisiae members: i) two plasma membrane proteins, the Mg2+ transporter Alr1p/Swc3p and the putative Mg2+ transporter, Alr2p, ii) two mitochondrial inner membrane Mg2+ transporters: Mfm1p/Lpe10p, and Mrs2p, and iii) and the vacuole membrane protein Mnr2p, a putative Mg2+ transporter. It also includes a family of Arabidopsis thaliana members (AtMGTs), some of which are localized to distinct tissues, and not all of which can transport Mg2+. Thermotoga maritima CorA and 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, Mrs2p, and Alr1p. Natural variants such as GVN and GIN, as in some ZntB family proteins, 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.