Uncharacterized bacterial subfamily of the Thermotoga maritima CorA-like family
This subfamily belongs to the Thermotoga maritima CorA (TmCorA)-like family of the MIT superfamily of essential membrane proteins involved in transporting divalent cations (uptake or efflux) across membranes. Members of the TmCorA-like family are found in all three kingdoms of life. It is a functionally diverse family which includes the CorA Co2+ transporter from the hyperthermophilic Thermotoga maritima, and three Saccharomyces cerevisiae proteins: two located in the plasma membrane: the Mg2+ transporter Alr1p/Swc3p and the putative Mg2+ transporter, Alr2p, and the vacuole membrane protein Mnr2p, a putative Mg2+ transporter. Thermotoga maritima CorA forms 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 by a related protein, Saccharomyces cerevisiae Alr1p. Natural variants in this signature sequence may be associated with the transport of different divalent cations. The functional diversity of the MIT superfamily may also be due to minor structural differences regulating gating, substrate selection, and transport.
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