This family, formerly known as DUF112, is a family of bacterial and archaeal tripartite tricarboxylate transporters of the extracytoplasmic solute binding receptor-dependent transporter group of families, distinct from the ABC and TRAP-T families [1]. TctA is part of the tripartite TctABC system which, as characterised in S. typhimurium [2], is a secondary carrier that depends for activity on the extracytoplasmic tricarboxylate-binding receptor TctC as well as two integral membrane proteins, TctA and TctB. complete three-component systems are found only in bacteria. TctA is a large transmembrane protein with up to 12 predicted membrane spanning regions in bacteria and up to 11 such in archaea, with the N-terminal within the cytoplasm. TctA is thought to be a permease, and in most other bacteria functions without TctB and TctC molecules [1].

1: The tripartite tricarboxylate transporter (TTT) family. Winnen B, Hvorup RN, Saier MH Jr; Res Microbiol. 2003;154:457-465. PMID:14499931

2: Tricarboxylate-binding proteins of Salmonella typhimurium. Purification, crystallization, and physical properties. Sweet GD, Kay CM, Kay WW; J Biol Chem. 1984;259:1586-1592. PMID:6141166