Transporter classification database

The "Transporter Classification Database" is the classification for membrane transport proteins recognized by the International Union of Biochemistry and Molecular Biology (IUBMB). The classification system was designed analogous to the EC number system for the classification of enzymes. Almost 400 transporter families are currently included in the Transporter Classification (TC) system. An important task of classification is to establish distant phylogenetic relationships between families and thus create superfamilies.

When creating a classification of transporter proteins (transporters), it would have been pointless to design a system simply on the basis of specificity to the substrate molecule or ion to be transported. Since data on amino acid sequences of different proteins, including transporters, are available via molecular biological investigation methods and new genomes are constantly being sequenced, TC classification is based on a dual weighting, which on the one hand includes the advantages of the enzyme system in grouping different entries (according to the type of reaction - i.e. transport) and on the other hand takes into account the sequence homology of the proteins involved. This type of classification has the advantage that in the vast majority of cases the phylogenetic relationships between the different entries can be clarified.

For example, the so-called ABC transporters form a large family of membrane proteins, which have an ATP binding cassette (ABC) as a common structural element and in which specific substrates are actively transported across a cell membrane.

In contrast to transport proteins, enzymes were classified according to the recommendations of the Enzyme Commission of the International Union of Biochemistry. The enzyme classification is based exclusively on the catalyzed reaction. It was assumed that proteins with similar catalytic functions are related and that they should be grouped together.

1. https://www.qmul.ac.uk/sbcs/iubmb/mtp/