Transporter Classification Database

The Transporter Classification Database (or TCDB) is an International Union of Biochemistry and Molecular Biology (IUBMB)-approved classification system for membrane transport proteins, including ion channels.[1][2][3]


The upper level of classification and a few examples of proteins with known 3D structure:

1. Channels and pores

1.A α-type channels

1.B. β-Barrel porins and other outer membrane proteins

1.C Pore-forming toxins (proteins and peptides)

1.D Non-ribosomally synthesized channels

1.E Holins

Main article: Holins

1.F Vesicle fusion pores

1.G Viral fusion pores

1.H Paracellular channels

1.I Membrane-bound channels

2. Electrochemical Potential-driven Transporters

2.A Porters (uniporters, symporters, antiporters)

2.B Nonribosomally synthesized porters

2.C Ion-gradient-driven energizers

3. Primary Active Transporters

3.A. P-P-bond hydrolysis-driven transporters

3.B Decarboxylation-driven transporters

3.C Methyltransfer-driven transporters

3.D. Oxidoreduction-driven transporters

They include a number of transmembrane cytochrome b-like proteins including coenzyme Q - cytochrome c reductase (cytochrome bc1 ); cytochrome b6f complex; formate dehydrogenase, respiratory nitrate reductase; succinate - coenzyme Q reductase (fumarate reductase); and succinate dehydrogenase. See electron transport chain.

3.E. Light absorption-driven transporters

4. Group Translocators

4.A Phosphotransfer-driven group translocators

Main article: PTS-GFL superfamily

4.B Nicotinamide ribonucleoside uptake transporters

4.C Acyl CoA ligase-coupled transporters

4.D Polysaccharide Synthase/Exporters

4.E. Vacuolar Polyphosphate Polymerase-catalyzed Group Translocators

5. Transport Electron Carriers

5.A Transmembrane 2-electron transfer carriers

5.B Transmembrane 1-electron transfer carriers


  1. Saier, Milton H.; Reddy, Vamsee S.; Tamang, Dorjee G.; Västermark, Åke (January 2014). "The Transporter Classification Database". Nucleic Acids Research. 42 (D1): D251–D258. doi:10.1093/nar/gkt1097. Retrieved 1 March 2016.
  2. Saier, M. H.; Yen, M. R.; Noto, K.; Tamang, D. G.; Elkan, C. (1 January 2009). "The Transporter Classification Database: recent advances". Nucleic Acids Research. 37 (Database): D274–D278. doi:10.1093/nar/gkn862. Retrieved 1 March 2016.
  3. Saier, M. H.; Tran, C. V.; Barabote, R. D. (1 January 2006). "TCDB: the Transporter Classification Database for membrane transport protein analyses and information". Nucleic Acids Research. 34 (90001): D181–D186. doi:10.1093/nar/gkj001. Retrieved 1 March 2016.

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