Solute carrier families 5 and 6-like; solute binding domainThis superfamily includes the solute-binding domain of SLC5 proteins (also called the sodium/glucose cotransporters or solute sodium symporters), SLC6 proteins (also called the sodium- and chloride-dependent neurotransmitter transporters or Na+/Cl--dependent transporters), and nucleobase-cation-symport-1 (NCS1) transporters. SLC5s co-transport Na+ with sugars, amino acids, inorganic ions or vitamins. SLC6s include Na+/Cl--dependent plasma membrane transporters for the monoamine neurotransmitters serotonin, dopamine, and norepinephrine, and the amino acid neurotransmitters GABA and glycine. NCS1s are essential components of salvage pathways for nucleobases and related metabolites; their known substrates include allantoin, uracil, thiamine, and nicotinamide riboside. Members of this superfamily are important in human physiology and disease. They contain a functional core of 10 transmembrane helices (TMs): an inverted structural repeat, TMs1-5 and TMs6-10; TMs numbered to conform to the SLC6 Aquifex aeolicus LeuT.