Properties of Families of Transport Proteins Included in the TC System (continued)

4. Group Translocators

Components of the bacterial phosphotransferase system PTS are included in this subclass. The product of the reaction, derived from extracellular sugar, is a cytoplasmic sugar phosphate. No transporters of the PTS group have been identified either in archebacteria or in eukaryotes.

TC no. a	Family	Substrates b	Size range c	Number of transmembrane segmentsd	Distributione	nf	Examples
4.A.1	Glc	glucose; N-acetylglucosamine; a- and b-glucosides (maltose; trehalose; sucrose; arbutin; arbutin, cellobiose, salicin)	c. 2000 (3 domains; dimeric)	(8)2	B	2	glucose IICB-IIA of Escherichia coli
4.A.2	Fru	fructose; mannitol	c. 2000 (3 domains; dimeric)	(6)2	B	2	fructose IIB'BC-IIAMH of Escherichia coli
4.A.3	Lac	lactose; cellobiose, N,N'-diacetylchitobiose; lichenan oligosaccharides	c. 2000 (3 domains; dimeric)	c. (8)2	B	2	lactose IICB-IIA of Staphylococcus aureus
4.A.4	Gut	glucitol	c. 2000 (3 domains; dimeric)	(8)2	B	1	glucitol IICBC'-IIA of Escherichia coli
4.A.5	Gat	galactitol, D-arabinitol	c. 2000 (3 domains; dimeric)	c. (8)2	B	1	galactitol IIC-IIB-IIA of Escherichia coli
4.A.6	Man	glucose, mannose, fructose; glucosamine, N-acetylglucosamine; sorbose; galactosamine; N-acetylgalactosamine	c. 2000 (4 domains; probably dimeric)	(6(IIC) + 1(IID))	B	!	mannose IIAB-IIC-IID of Escherichia coli

5. Transmembrane Electron Carriers

5.A Two-electron carriers

TC no. a	Family	Substrates b	Size range c	Number of transmembrane segmentsd	Distributione	nf	Examples
5.A.1	DsbD	2e-	150-800	6-9	A, B	2	DsbD of E.coli
5.A.2	DsbB	2e-	150-200	4	B	1	DsbB of Escherichia coli

5.B One-electron carriers

TC no. a	Family	Substrates b	Size range c	Number of transmembrane segmentsd	Distributione	nf	Examples
5.B.1	Gp91 phox	e-	450-750	6	B, E	2	Gp91phox of Homo sapiens

8. Accessory Factors Involved in Transport

Proteins that in some way facilitate transport across one or more biological membranes but do not themselves participate directly in the transmembrane translocation of a substrate are included in this subclass. They may provide a function connected with energy coupling to transport, play a structural role in complex formation, serve a biogenic or stability function or function in regulation.

TC no. a	Family	Substrates b	Size range c	Number of transmembrane segmentsd	Distributione	nf	Examples
8.A.1	MFP	proteins; peptides; lipooligosaccharides; drugs, dyes, signalling molecules; heavy metal ions; etc.	350-500	1	B	2	EmrA of Escherichia coli
8.A.2	SAL	proteins, peptides	100-150	0-1	B(G-)	1	PulS of Klebsiella pneumonia
8.A.3	MPA1	complex polysaccharides	600-800	2	B	2	ExoP of Rhizobium meliloti
8.A.4	MPA2	complex polysaccharides	300-400	2	B	2	KpsE of Escherichia coli
8.A.5	VICb	K+	200-550	2	B, E	2	b1a of Homo sapiens
8.A.6	ANT	nutrients	c. 3000	2	E	0	CSF1 of Saccharomyces cerevisiae
8.A.7	EI	sugars	500-600	0	B	1	phosphotransferase enzyme 1 of Escherichia coli
8.A.8	HPr	sugars	60-95	0	B	1	HPr of Escherichia coli
8.A.9	rBAT	cationic and neutral amino acids (uptake)	500-700	4	E(An)	2	rBAT of Oryctolagus cuniculus
8.A.10	MinK	K1	100-200	1	E(An)	2	MinK of Rattus norvegicus
8.A.11	PLB	Ca2+	c. 50	1	E(An)	2	PLB of Homo sapiens
8.A.12	BEA	bacteriocins	100-200	1	B(G+)	0	BrcD of Brochothrix campestris
8.A.13	Tpr1	K+, alkali metal ions	c. 1040	1	A, B, E	2	Tpr1 of Schizosaccharomyces pombe

9. Incompletely Characterized Transport Systems

Transport protein families of unknown classification are grouped here, awaiting their final placing once their transport mode and energy coupling have been established. These families include at least one member for which a transport function has been described but either the mode of transport or the energy coupling is not known.

TC no. a	Family	Substrates b	Size range c	Number of transmembrane segmentsd	Distributione	nf	Examples
9.A.1	PST	polysaccharides (export)	400-500	12	B	2	lipopolysaccharide exporter RfbX1 of Escherichia coli
9.A.2	MerTP	Hg2+ (uptake)	c. 200	3	B	2	mercuric ion transporter MerTP encoded on the IncJ plasmid pMERPH of Shewanella putrefaciens
9.A.3	MerC	Hg2+ (uptake)	c. 140	4	B	1	mercuric ion uptake transporter MerC encoded on the IncJ plasmid pMERPH of Shewanella putrefaciens
9.A.4	PnuC	nicotinamide mononucleotide (uptake)	c. 320	7	B	1	nicotinamide mononucleotide uptake transporter PnuC of Salmonella typhimurium
9.A.5	PPI	peroxisomal proteins	multimeric subunits	3-5(10p) + 2-4(12p) + 1-2(13p) + 0-1(14p) + 0-1(5p) + 0-2(7p) + 0-1(4p)	E	1	PEX of Homo sapiens
9.A.6	INT	nucleosides	200-300	E (An)	2		intracellular nucleoside transporter MTP of Mus musculus
9.A.7	MerF	Hg2+	c. 80	2	B	2	MerF importer of Pseudomonas aeruginosa plasmid
9.A.8	FeoB	Fe2+ (uptake)	c. 800	8-13	A, B	2	Fe2+ uptake transporter FeoB of Escherichia coli
9.A.9	FeT	Fe2+ (Co2+, Cd2+) (uptake)	c. 550	6	E (Y)	0	Fe2+ transporter Fet4p of Saccharomyces cerevisia
9.A.10	OFeT	Fe2+ (uptake)	c. 400	6	A, B, E	2	oxidase-dependent Fe2+ transporter Ftr1p of Saccharomyces cerevisiae
9.A.11	Ctr1	Cu2+ (uptake)	c. 400	2-3	E (Y)	1	copper transporter Ctr1p of Saccharomyces cerevisiae
9.A.12	Ctr2	Cu2+ (uptake)	150-200	3	E	1	copper transporter Ctr2p of Saccharomyces cerevisiae
9.A.13	Cjl	colicins Js	c. 65	0	B	0	Cjl of Shigella sonnei
9.A.14	NPC	RNA; proteins, small molecules, etc.	30-50 proteins	multiple	E	1	nuclear pore complex of Saccharomyces cerevisiae
9.A.15	YhaG	tryptophan	150-200	6	B	0	YhaG of Bacillus subtilis
9.A.16	LPI	protein	c. 400	2	E	1	LAMP of Homo sapiens
9.A.17	PbrT	Pb2+	400-650	7	B	1	PbrT of Ralstonia metallidurans
9.A.18	PUP	peptides, microcins, antibiotics (uptake)	c. 400	7	B	1	microbin uptake porter SbmA of Escherichia coli
9.A.19	MgtE	Mg2+, Co2+ (uptake)	300-500	4-5	A, B	2	Mg2+-transporter MgtE of Bacillus firmus
9.A.20	LCT	univalent cations	c. 570	8-10	E (Pl)	0	low-affinity cation transporter LCT1 of Triticum aestivum
9.A.21	ComC	DNA, proteins	1000-1250	multiple	B(G-)	1	pilus assembly protein of Neisseria meningitidis
9.A.22	NhaE	Na+, K+	c. 250	7-9	B		NhaE of Bacillus subtilis
9.A.23	FP	Fe2+; H+	400-800	8-10	E(An,Pl)		Mus musculus ferroportin IREG1

^b Substrates of single transporters within a family are separated by commas; substrates transported by different protein members of the family are separated by semicolons. When various solutes serve as transported substrates, they are separated by a slash; when two different solutes are transported in a symport fashion, they are separated by a comma; when two or more substrates are transported in an antiport fashion they are separated by a colon.

^c Size range (in number of amino acid residues) when a single type of subunit is present, or for the entire complex when several types of subunits are present. In some cases the individual subunits in multisubunit systems are indicated separately.

^d Number of (putative) transmembrane a-helical segments, TMS, (or b-strands in section 1.B) in a polypeptide chain. Underlined numbers indicate that the number is established by X-ray chrystallographic data or that substantial experimental evidence suggests the proposed topology, usually as a result of the use of gene fusion technology. If not underlined, numbers indicate the number of TMS predicted on the basis of hydropathy analysis using available programs such as WHAT and AveHAS see the Web site at (http://www.biology.ucsd.edu/~yzhai/biotools.html). In some cases, the numbers of predicted TMS is zero, and hence a "0" is entered. In many such cases, the actual TMS is (are) amphipathic, and hence the program does not predict the number correctly. Subscripts refer to the number of polypeptide chains in the complex when known; n indicates an oligomeric structure of unknown or poorly defined number of subunits. If alternative structures are found for different transporters within a single family, these are separated by semicolons.

^e Abbreviations used for types of organisms, organelles and viruses are as follows: B, Bacteria; A, Archaea; E, Eucarya; G^-, Gram-negative bacteria; G⁺, Gram-positive bacteria; Y, yeasts; Fu, fungi; Pr, protozoans; Pl, plants; An, animals; Mito, mitochondria; Chloro, chloroplasts; ER, endoplasmic reticulum; Bp, bacteriophage; V, virus

^f The numbers represent the order of magnitude of members in this family as of November 2001. 0: between 1 and 5; 1: between 6 and 49; 2: between 50 and 499; 3: more than 500.