<p> This family is one of at least three major families of extracytoplasmic solute receptor (ESR) for TRAP (Tripartite ATP-independent Periplasmic Transporter) transporters. The others are the DctP (<db_xref db="INTERPRO" dbkey="IPR004682"/>) and SmoM (<db_xref db="INTERPRO" dbkey="IPR004682"/>) families. These transporters are secondary (driven by an ion gradient) but composed of three polypeptides, although in some species the 4-TM and 12-TM integral membrane proteins are fused. Substrates for this transporter family are not fully characterised but, besides C4 dicarboxylates, may include mannitol and other compounds [<cite idref="PUB00015015"/>].</p> TRAP transporter solute receptor, TAXI family