These probable extra-cytoplasmic solute receptors are strongly overrepresented in several beta-proteobacteria [1]. This family, formerly known as Bug - Bordetella uptake gene (bug) product - is a family of bacterial tripartite tricarboxylate receptors of the extracytoplasmic solute binding receptor-dependent transporter group of families, distinct from the ABC and TRAP-T families [3]. The TctABC system has been characterised in S. typhimurium [2], and TctC is the extracytoplasmic tricarboxylate-binding receptor which binds the transporters TctA and TctB, two integral membrane proteins. Complete three-component systems are found only in bacteria [2].

1: Overrepresentation of a gene family encoding extracytoplasmic solute receptors in Bordetella. Antoine R, Jacob-Dubuisson F, Drobecq H, Willery E, Lesjean S, Locht C; J Bacteriol 2003;185:1470-1474. PMID:12562821

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

3: 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