The sodium/substrate symporter family: structural and functional features

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Abstract
Members of the sodium/substrate symporter family (SSSF, TC 2.A.21) catalyze the uptake of a wide variety of solutes including sugars, proline, pantothenate, and iodide into cells of pro‐ and eukaryotic origin. Extensive analyses of the topology of different SSSF proteins suggest an arrangement of 13 transmembrane domains as a common topological motif. Regions involved in sodium and/or substrate binding were identified. Furthermore, protein chemical and spectroscopic studies reveal ligand‐induced structural alterations which are consistent with close interactions between the sites of sodium and substrate binding, thereby supporting an ordered binding mechanism for transport.