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Topologies and three dimensional structures of (a and b) the halophilic heptaspan membrane proteins BR (PDB-code 1C3W) and HR (PDB-code 1E12), and (c and d) the dodecaspan sodium-proton antiporter NhaA (PDB-code 1ZCD) from Escherichia coli. The helices are labeled A–G in the case of BR and HR and I–XII in the case of NhaA.
