Membrane transport proteins

After more than a decade of systematic work of M.H. Saier Jr. and his co-workers, and after some five years of discussions with members of the Nomenclature Committee of IUBMB, headed by A. Kotyk, a list of over 400 families of membrane transport proteins is now accessible on the Web at https://iubmb.qmul.ac.uk/mtp/. The document contains three sections:

(1) List of families and subfamilies of the transport classification (TC) system,

(2) Properties of families of transport proteins included in the TC system,

(3) Classification of transport proteins according to specificity.

The system uses a five-character code: the first character (a number) designates the class of proteins, the second character (a letter) designates the subclass, both of these referring to the mechanism of translocation or the source of energy used for the process; the third character (a number) specifies the transporter family, the fourth character (a number) the subfamily. These hierarchical levels are defined on the basis of their primary structure. The fifth characer (a number) then refers to a particular transport protein. In outline, the transport proteins are classified as follows:

1. Pores and channels

1.A alpha-Helical channels 36 families

1.B beta-Strand porins 34 families

1.C Pore-forming toxins 58 families

1.D Non-ribosomally synthesized channels 10 families

1.E Holins 19 families

2. Electrochemical-potential-driven transporters

2.A Transporters (uniporters, symporters and antiporters 80 families

2.B Non-ribosomally-synthesized transporters 16 families

3. Primary active transporters

3.A P-P-bond-hydrolysis-driven transporters 14 families

3.B Decarboxylation-driven transporters 1 family

3.C Methyl-transfer-driven transporters 1 family

3.D Oxidoreduction-driven transporters 9 families

3.E Light-driven transporters 2 families

4. Group translocators

4.A. Phosphotransferases 6 families

5. Transmembrane electron carriers

5.A Two-electron carriers 2 families

5.B One-electron carriers 1 family

8. Accessory factors involved in transport

8.A Auxiliary transport proteins 13 families

9. Incompletely characterized transport proteins

9.A Transporters of unknown classification 23 families

Return to 2004 Newsletter Contents page

1.	Pores and channels
	1.A	alpha-Helical channels	36 families
	1.B	beta-Strand porins	34 families
	1.C	Pore-forming toxins	58 families
	1.D	Non-ribosomally synthesized channels	10 families
	1.E	Holins	19 families
2.	Electrochemical-potential-driven transporters
	2.A	Transporters (uniporters, symporters and antiporters	80 families
	2.B	Non-ribosomally-synthesized transporters	16 families
3.	Primary active transporters
	3.A	P-P-bond-hydrolysis-driven transporters	14 families
	3.B	Decarboxylation-driven transporters	1 family
	3.C	Methyl-transfer-driven transporters	1 family
	3.D	Oxidoreduction-driven transporters	9 families
	3.E	Light-driven transporters	2 families
4.	Group translocators
	4.A.	Phosphotransferases	6 families
5.	Transmembrane electron carriers
	5.A	Two-electron carriers	2 families
	5.B	One-electron carriers	1 family
8.	Accessory factors involved in transport
	8.A	Auxiliary transport proteins	13 families
9.	Incompletely characterized transport proteins
	9.A	Transporters of unknown classification	23 families