This family mainly consists of Transmembrane subunit (TM) found in Periplasmic Binding Protein (PBP)-dependent ATP-Binding Cassette (ABC) transporters which generally bind type 2 PBPs, such as Binding-protein-dependent transport systems inner membrane component and Maltose transport permease MalF. It is around 580 residues in length and is mainly found in various species, such as Thermotoga, Dictyoglomus, Thermosipho, Fervidobacterium, Mesotoga and so on. The function of this family is unknown.