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.

Classification

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

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

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

8. Accessory factors involved in transport

8.A Auxiliary transport proteins

8.B Ribosomally synthesized protein/peptide toxins that target channels and carriers

8.C Non-ribosomally synthesized toxins that target channels and carriers

9. Incompletely characterized transport systems

9.A Recognized transporters of unknown biochemical mechanism

9.B Putative transport proteins

9.C Functionally characterized transporters lacking identified sequences