Bacterial high affinity transport systems are involved in active transport of solutes across the cytoplasmic membrane. Most of the bacterial ABC (ATP-binding cassette) importers are composed of one or two transmembrane permease proteins, one or two nucleotide-binding proteins and a highly specific periplasmic solute-binding protein. In Gram-negative bacteria the solute-binding proteins are dissolved in the periplasm, while in archaea and Gram-positive bacteria, their solute-binding proteins are membrane-anchored lipoproteins [, ].On the basis of sequence similarities, the vast majority of these solute-binding proteins can be grouped into eight families of clusters, which generally correlate with the nature of the solute bound. Family 3 groups together specific amino acids periplasmic proteins, such as HisJ [], and opine-binding periplasmic proteins, such as NocT []. This entry include a subset of the family 3.
