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Saccharomyces cerevisiae Alr1p-like subfamily This eukaryotic subfamily belongs to the Thermotoga maritima CorA (TmCorA)-family of the MIT superfamily of essential membrane proteins involved in transporting divalent cations (uptake or efflux) across membranes. This subfamily includes three Saccharomyces cerevisiae members: two plasma membrane proteins, 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 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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