Table 3.

Properties of families of transport systems included in the TC system

TC no.FamilySubstrate(s)aSize rangeb (no. of residues)nTMSscOrganismsdNo. of membersExamples
1.A.  α-Type channel-forming proteins and peptides
 1.A.1VICNa+; K+; Ca2+; multiple cationsWidely varied(2)4; (4)2; (6)4; (8)2; (12)2; (24)1; often heterooligomericE, A, B>500Voltage-gated Na+ channels; voltage-gated Ca2+ channels; K+ channels sensitive to voltage, Ca2+, or cyclic nucleotides of Homo sapiens
 1.A.2IRK-CK+390–430(2)nE (An)>10Inward rectifier K+ channels (ATP activated or G-protein regulated) of Homo sapiens
 1.A.3RIR-CaCCa2+5,000 or 2,500(6)nE (An)>10Ryanodine receptor Ca2+ channels; inositol 1,4,5-triphosphate receptor Ca2+ channels of Homo sapiens
 1.A.4TRP-CCCa2+800; 1,300(6)nE (An)>10Transient receptor potential Ca2+ channel (TRP) of Drosophila melanogaster
 1.A.5PCCNa+, K+, Ca2+4,00016–18E (An)3Polycystin 1 ofHomo sapiens
 1.A.6ENaCNa+; cations640–700(2)3E (An)>20Epithelial Na+ channels; degenerins; peptide-gated ionotropic receptors of animals
 1.A.7ACCCations (monovalent cations; Ca2+)380–600(2)nE (An)10ATP-gated cation channel (P2X1) of Homo sapiens
 1.A.8MIPH2O; glycerol, urea, polyols, NH3, CO2220–310(6)2 or 4B, A, E>100Aquaporins (Aqp1) of Homo sapiens; glycerol facilitators (GlpF) of E. coli
 1.A.9LICCations or chloride400–500(3–5)5; often heterooligomericE (An)>100Acetylcholine or serotonin-activated cation channels; glycine, glutamate or GABA-regulated Cl channels of Homo sapiens
 1.A.10GICMonovalent cations and Ca2+800–1,000(3–5)5E (An)10Glutamate-regulated ionotropic channels of Rattus norvegicus
 1.A.11ClCCl, anions400–1,00010–12B, A, E>30Voltage-gated Cl channel (ClCl) of Homo sapiens
 1.A.12O-ClCCl, anions240–440(2)nE (An)>10Organellar voltage-sensitive Cl channels of Bos taurus
 1.A.13E-ClCCl, anions900–1,000(4)nE (An), B>20Ca2+-activated Cl channel-2 ofHomo sapiens
 1.A.14NSCC1Monovalent cations: Na+, Li+, K+423(4)nE (An)1Nonselective cation channel (NSC1) of Mus musculus
 1.A.15NSCC2Monovalent cations: Na+, K+, Cs+ as well as Ca2+(slow)283–402(2)nE (An, Y, F)>10Nonspecific channel translocation protein-1 (NS1) ofHomo sapiens; Sec62 of Saccharomyces cerevisiae
 1.A.16Mid1Ca2+5401 or 2E (Y)2Mid1 of Saccharomyces cerevisiae
 1.A.17CSCIons; solutes177β-Structure?E (Pl)1Chloroplast outer envelope solute channel (CSC) of Pisum sativum
 1.A.18Tic110Anions; proteins1,0002E (Pl)1Protein import-related anion-selective channel (Tic110)
 1.A.19IVCH+∼100(1)n (n= 4?)E (influenza virus)1Matrix protein (M2) of influenza virus
 1.A.20CybBH+7406E (Pl, An)∼20gp91phox human phagocyte NADPH oxidase-associated cytochrome b558H+ channel
 1.A.22MscLProteins, ions (slightly cation selective)130–140(2)6B10Large mechanosensitive ion channels (MscL) of E. coli
 1.A.23MscSIons (slight anion selectivity)240–1,1202–14B, A∼50Small conductance mechanosensitive ion channel (KefA) of E. coli
 1.A.24ConnexinSmall molecules (no discrimination)200–600(4)nE (An)>50Vertebrate connexin 43 (gap junction α-1 protein) (CX43) of Rattus norvegicus
 1.A.25InnexinSmall molecules (no discrimination)300–600(4)nE (An)>50Invertebrate innexin (UNC-7) of Caenorhabditis elegans
 1.A.26SATNH4+346(1)nE (Pl)1Symbiotic NH4+ transporter-1 (SAT1) of Glycine max
 1.A.27PLMCl (anion selective), taurine, lactate, glutamate, isethionate, gluconate70–100(1)nE (An)>10Phospholemman; Cl conductance inducer protein Mat-8
 1.A.28–1.A.43Holin functional superfamily (16 families)Proteins; small molecules70–150(2–4)nB, phage, plasmids>50Lysis protein S of phage lambda
 1.A.44UTUrea, water380–40010E (An)>10Kidney vasopressin-regulated urea transporter (UT2)
 1.A.45MotH+; Na+500–1,000 (2 subunits)4 (A) + 1 (B)B∼10H+uptake-driven flagellar motor (MotAB) of E. coli
1.B. Outer membrane porins (β-structure)
 1.B.1–1.B.26eVarious outer membrane porins and export proteins250–1,0008–24 β-strandsG-B; phage; E (mito, plastids)>200OmpF ofE. coli; VDAC of Bos taurus; AidA ofE. coli
1.C. Toxins
 1.C.1ColicinIons; small molecules500–700 (150–180 for the channel domain)(4?)nB, plasmids10Colicin E1 of E. coli
 1.C.2IPCIons; small molecules500–1,300 (∼220 for the channel domain)(6?)nB>50Cry3A insecticidal γ-endotoxin of Bacillus thuringiensis
 1.C.3αHLIons; small molecules300–400(2β)7B>10α-Hemolysin of Staphylococcus aureus
 1.C.4AerolysinIons; small molecules440–490(2β)7B, E (Pl)7Aerolysin of Aeromonas hydrophila
 1.C.5ɛ-ToxinIons; small molecules330?B∼10ɛ-Toxin ofClostridium perfringens
 1.C.6YKT-K1Cation selective300?E (Y)1Yeast killer toxin ofSaccharomyces cerevisiae
 1.C.7DTDT, A-chain (protein)340?B1Diphtheria toxin (DT) of corynebacteriophage β
 1.C.8BTTBTT, L-chains800(2?)nB>10Botulinum and tetanus toxin channels of Clostridium species
 1.C.9VacAIons; small molecules1,290(?)6B1VacA ofHelicobacter pylori
 1.A.21Bcl-2Protein (cytochromec)200–240(1–5)n (n= 2?)E (An)>20Apoptosis regulator [Bcl-X(L)] ofHomo sapiens
 1.C.10HlyEIons/moderately cation selective305?B1HlyE of E. coli
 1.C.11RTX-toxinIons; small molecules900–1,100?B>10Hemolysin A (HlyA) ofE. coli
 1.C.12TACIons; small molecules470–580?B>50Perfringolysin O ofClostridium perfringens
 1.C.13CtxIons286?B1Leucocidin cytotoxin (Ctx) of Pseudomonas aeruginosa phage phiCTX
 1.C.14CHLIons and other solutes500–800?B∼10Cytohemolysin (HlyA) ofVibrio cholerae
 1.C.15WSPSmall molecules400?An2Whipworm stichosome porin ofTichuris trichiura
 1.C.16–1.C.30Channel-forming peptide functional superfamily (15 families)Ions25–75 small peptides, often from large precursors(1 or 2)nB, A, E>1,000Maganins; cecropins; melittin, defensins; bacteriocins
 1.C.31Colicin VIons; small molecules100(1–2)nB (plasmid)1Colicin V of E. coli
 1.C.32MastoparanSmall molecules13–14(1)nE (insects)>10Mastoparan of Vespa xanthoptera
 1.C.33CathilicidinSmall molecules90–220 (precursor), 18 (mature)(1)nE (An)>10premyeloid cathilicidin 1 of Equus caballus
 1.C.34TachyplesinSmall molecules18–77(1)nE (An)>10Tachyplesin I of Tachyplesus tridentatus
 1.C.35AmoebaporeSmall molecules90–100(1)nE (Pr)>10Amoebapore of Entamoeba histolytica
 1.C.36IIITCPProteins300–600(2)nB>20Type III protein secretion target cell pore protein (YopB) of Yersinia pseudotuberculosis
 1.C.37Lactococcin 972Small molecules60–90(1)nB1Lactococcin 972 of Lactococcus lactis
 1.C.38EquinatoxinSmall molecules170–220(1)3 or 4An (sea urchins)>10Equinatoxin ofActinia tenebrosa
2.A.  Carrier-type facilitators
 2.A.1MFSVarious small molecules400–60012 or 14B, A, E>1,000Lactose permease (LacY) of E. coli; drug efflux permease (EmrD) ofE. coli
 2.A.2GPHSugars∼50012B, A, E (An, Pl)>20Melibiose permease (MelB) of E. coli
 2.A.3APCAmino acids, polyamines, choline440–63012B, A, E>100Lysine permease (LysP) of E. coli
 2.A.4CDFCd2+, Co2+, Ni2+300–7506B, A, E>10Heavy-metal uptake and efflux permeases of bacteria, eukaryotic plasma membranes, and mitochondria (CzcD ofRalstonia eutropha)
 2.A.5ZIPZn2+, Fe2+220–4308E (Y, Pl, An)>10Zinc uptake transporter (Zrt1) of Saccharomyces cerevisiae
 2.A.6RNDHeavy metal ions; multiple drugs; oligosaccharides; organic solvents, fatty acids, phospholipids; cholesterol800–1,200∼12B, A, E>100Drug efflux pump (AcrA) of E. coli
 2.A.7SMRMultiple drugs and dyes (mostly cationic)110(4)3B>20Cationic drug efflux pump (Smr) of Staphylococcus aureus
 2.A.8GntPGluconate, iodonate45012–14B>10Gluconate permease (GntP) ofBacillus subtilis
 2.A.9RhaTSugars280–34010B5Rhamnose transporter (RhaT) of E. coli
 2.A.10KDGT2-Keto-3-deoxygluconate40010–12B52-Keto-3-deoxygluconate transporter (KdgT) of Erwinia chrysanthemi
 2.A.11CitMHSCitrate40012B5Citrate:Me2+:H+symporter (CitM) of Bacillus subtilis
 2.A.12AAAATP, ADP50012B, E (Pl)>10ATP/ADP exchange translocase of Rickettsia prowazekii
 2.A.13DcuC4-dicarboxylates44012G−B5Dicarboxylate uptake porter-A (DcuA) of E. coli
 2.A.14LctPLactate510–51612B, A10Lactate permease (LctP) of E. coli
 2.A.15BCCTGlycine betaine; carnitine; choline480–68012B10Carnitine transporter (CaiT) ofE. coli
 2.A.16TDTTellurite; dicarboxylates320–44010B, A, E>10Tellurite uptake permease (TehA) of E. coli
 2.A.17POTPeptides; nitrates; amino acids450–60012B, E>30Dipeptide transporter (DtpT) of Lactococcus lactis
 2.A.18AAAPAmino acids and their derivatives400–71011E (An, Pl, Y, F)>30Amino acid/auxin:H+ symporter (Aux-1) of Arabidopsis thaliana
 2.A.19CaCACa2+460–1,20010–12B, A, E>30Ca2+:H+ antiporter (ChaA) ofE. coli
 2.A.20PiTInorganic phosphate410–68010–12B, A, E>20Phosphate transporter (PitA) of E. coli
 2.A.21SSSSugars; amino acids; vitamins; nucleosides; inositols; iodide; urea400–70012–15B, A, E>30Pantothenate:Na+ symporter (PanF) of E. coli
 2.A.22NSSNeurotransmitters; amino acids; osmolytes; taurine; creatine600–70012B, A, E (An)>50Serotonin:Na+ symporter of Homo sapiens
 2.A.23DAACSC4-dicarboxylates; acidic and neutral amino acids420–58010–12B, A, E>20Glutamate/aspartate permease (GltP) of E. coli
 2.A.24CCSMono-, di-, and tricarboxylates45012B>10Citrate:Na+symporter (CitS) of Klebsiella pneumoniae
 2.A.25AGCSAlanine, glycine440–5408–12B10Alanine/glycine transporter (DagA) of Alteromonas haloplanktis
 2.A.26LIVCSBranched-chain amino acid∼44012B10Branched-chain amino acid transporter (BraB) of Pseudomonas aeruginosa
 2.A.27ESSGlutamate∼40012B5Glutamate:Na+symporter (GltS) of E. coli
 2.A.28BASSBile acids360–48012B, E (An)10Bile acid uptake system of Rattus norvegicus
 2.A.29MCATP/ADP; Pi; organic anions; H+; carnitine/acyl carnitine; basic amino acids; FAD3006E (mito)>100ATP/ADP exchanger ofHomo sapiens
 2.A.30CCCK+, Na+, Cl1,000–1,20012B, A, E (An, Pl, Y)>30NaCl/KCl cotransporter of Rattus norvegicus
 2.A.31AEInorganic anions900–1,25014E (An, Y)>20Anion exchanger (AE1) of Homo sapiens
 2.A.32SitSilicate55012E (diatoms)6Sit1 of Cylindrotheca fusiformis
 2.A.33NhaANa+/H+∼40012B10Na+:H+antiporter (NhaA) of E. coli
 2.A.34NhaBNa+/H+∼52012B5Na+:H+antiporter (NhaB) of E. coli
 2.A.35NhaCNa+/H+∼46012B5Na+:H+antiporter (NhaC) of Bacillus firmus
 2.A.36CPA1Na+/H+; Na+ or K+/H+500–90010–12B, A, E>40Na+:H+ antiporter (Nhe-1) ofRattus norvegicus
 2.A.37CPA2Na+/H+ or K+/H+330–63010–12B, A, E>20K+ efflux protein-C (KefC) of E. coli
 2.A.38TrkK+:H+?420–56010–12B, A, E>10K+ uptake permease (TrkH) of E. coli
 2.A.39NCS1Nucleobases; thiamine; nucleosides420–64012B, A, E>20Cytosine permease (CodB) of E. coli
 2.A.40NCS2Nucleobases; urate420–60012B, A, E>20Uracil permease (UraA) ofE. coli
 2.A.41CNTNucleosides390–66012–14B, A, E>20Nucleoside:H+ symporter (NupC) of E. coli
 2.A.42HAAAPHydroxy and aromatic amino acids400–45011B>20Tyrosine permease (TyrP) ofE. coli; serine permease (SdaC) of E. coli
 2.A.43LCTCystine300–4007E (An, Pl, Y)>20Lysosomal cystine transporter (cystinosin) of Homo sapiens
 2.A.44FNTFormate; nitrite; acetate250–6306–8B, A, E (Y)>10Formate efflux permease (FocA) of E. coli
 2.A.45ArsBArsenite, antimonite400–90012B, A, E>20Arsenical resistance efflux pump of Staphylococcus aureus
 2.A.46BenEBenzoate40012B2Benzoate:H+symporter (BenE) of Acinetobacter calcoaceticus
 2.A.47DASSDicarboxylates; phosphate; sulfate430–92011–14B, A, E>20Dicarboxylate translocator (SodiT1) of Spinacia oleracea
 2.A.48RFCReduced folate500–60012E (An)>10Reduced folate carrier (RFC) of Mus musculus
 2.A.49AmtAmmonium390–62012B, A, E>20Ammonium transporter (AmtB) of E. coli
 2.A.50TP-NSTTriosephosphates; glucose 6-phosphate, Pi; nucleotide sugars; nucleotides300–4505–12E (An, Pl, Y) (chloroplasts; plastids; other organelles)>20Triosephosphate translocator (TPT) of Zea mays chloroplasts; UDP-galactose:UDP exchange transporter of Homo sapiens endoplasmic reticulum and Golgi
 2.A.51CHRChromate; sulfate (uptake or efflux)∼40010B, A∼10Chromate transporter (ChrA) of Alcaligenes eutrophus
 2.A.52NiCoTNi2+, Co2+300–4008B>10Ni2+uptake permease (HoxN) of Ralstonia eutropha
 2.A.53SulPSulfate430–90010–13B, A, E>50Sulfate permease (SulP) of Homo sapiens
 2.A.54MTCDi- and tricarboxylates∼2903–6E (mito)>10Mitochondrial tricarboxylate carrier (MTC) of Rattus norvegicus
 2.A.55NrampDivalent metal ions (uptake)540–5808–12B, A, E∼20Divalent metal ion; H+ symporter (Nramp2) of Homo sapiens
 2.A.56TRAP-TC4-dicarboxylates; acidic amino acids; sugars?∼1,000 (three components)12 + 4B, A>20Dicarboxylate transporter (DctPQM) of Rhodobacter capsulatus
 2.A.57ENTNucleosides∼45011E>10Equilibrative nucleoside transporter-1 (hENT1) of Homo sapiens
 2.A.58PNaSInorganic phosphate300–650>10B, E>20Renal Na+-dependent phosphate transporter-2 (NPT2) of Rattus norvegicus
 2.A.59ACR3Arsenite40010B, A, E1Arsenical resistance-3 protein (ACR3) of S. cerevisiae
 2.A.60OATOrganic anions; prostaglandins; bile acids; bile conjugates600–70010–12E (An)10Organic anion transporter (OATP1) of Rattus norvegicus; prostaglandin transporter (PGT) of Rattus norvegicus
 2.A.61DcuCDicarboxylates46110–12B10C4-dicarboxylate uptake-C porter (DcuC) of E. coli
 2.A.62NhaDNa+/H+410–43010–12B, A3Na+/H+ antiporter (NhaD) ofVibrio parahaemolyticus
 2.A.63CPA3K+ or Na+/H+>700; possibly multiple components17 (+?)B2K+:H+antiporter (PhaA-G) of Rhizobium meliloti; Na+:H+ antiporter (Nha1) of an alkalophilicBacillus species
 2.A.64TatRedox proteins>800 (5 subunits)9 (1+1+5 or 6+0+1)B, A, E>10Redox protein targeting and translocation (MttA-E) (TatA-E) system of E. coli
 2.A.65BRTBilirubin3405E (An)1Bilirubin transporter of Rattus norvegicus
 2.A.66MATEDrugs400–70012B, A, E>40Norfloxacin and other drug efflux pump (NorM) ofVibrio parahaemolyticus
 2.A.67OPTPeptides600–90012–15B, A, E>20Oligopeptide transporter (OPT1) of Candida albicans
 2.A.68AbgTAminobenzoylglutamate∼50012–13B1Aminobenzoylglutamate transporter (AbgT) of E. coli
 2.A.69AECAuxin (efflux)600–7008–12B, A, E∼20Auxin efflux carrier (PIN1)
 2.A.70MSSMalonate255 + 1297 + 4B<10Malonate:Na+symporter (MadLM) of Malonomonas rubra
 2.A.71FBTFolate, biopterin, methotrexate450–65012B, E (Pr, Pl)<10Folate-biopterin transporter of Leishmania donovani
 2.A.72KUPK+(uptake)400–80012B, E (Y, Pl)∼30The K+:H+ symporter (Hak1) of Neurospora crassa
 2.A.73ICTHCO3380–48010B3HCO3:Na+symporter of Synechococcus PCC7942
 2.A.74METThymidine, drugs, steroids230–2704E (An)5Lysosomal hydrophobe/ amphiphile transporter (MTP) of Mus musculus
 2.A.75LysEBasic amino acids190–2405B10Lysine/arginine exporter (LysE) ofCorynebacterium glutamicum
 2.A.76RhtBNeutral amino acids and their derivatives190–2305B10Neutral amino acid exporter (RhtB) of E. coli
 2.A.77CadDCd2+; cations190–2205B4Cadmium resistance protein (CadD) of Staphylococcus aureus
 2.A.78CAATCarboxylates, amino acids, amines (efflux)280–32010B, A>50MadN of Malonomonas rubra
2.C.  Ion gradient-driven energizers
 2.C.1TonBH+?; drives solute uptake across outer bacterial membranes∼1,0001 + 3 + 1B>10TonB-ExbBD outer membrane energizer of E. coli
3.A.  Pyrophosphate bond hydrolysis-driven transporters
 3.A.1ABCAll sorts of inorganic and organic molecules of small, intermediate, and large sizes, from simple ions to macromolecules1,000–2,000 (multidomain; usually multisubunit10 or 12; variableB, A, E>1,000Maltose permease (MalEFGK) of E. coli; multidrug resistance protein (MDR) of Homo sapiens
 3.A.2F-ATPaseH+; Na+>4,000 (multiple subunits)(2)12, + (1)2, + (6)1B, A, E (chloro; mito)>100F0F1-ATPase of E. coli
 3.A.3P-ATPaseNa+; H+; K+; Ca2+; Mg2+; Cd2+; Cu2+; Zn2+, Cd2+, Co2+, Ni2+; Ag+; phospholipids (flipping)600–1,200 (sometimes multisubunit)6–12B, A, E>100KdpABC (K+ uptake) of E. coli
 3.A.4ArsABArsenite, antimonite, tellurite∼1,100 (multidomain; two subunits)12B, A, E>10Arsenite efflux pump (ArsAB) of E. coli
 3.A.5IISPProteins>2,000 (multiple subunits)SecY (10)B, A, E>50Type II secretory pathway system (SecAYEDFG) of E. coli
 3.A.6IIISPProteins>2,000 (multiple subunits)6 integral membrane constituentsB>20Type III secretory pathway system (YscNDRSTUC; LcrD) of Yersinia species
 3.A.7IVSPProteins, protein-DNA complexes>2,000 (multiple subunits)3 integral membrane constituentsB>20Type IV secretory pathway system (VirB4, B6, B7, B9, B10, B11) of Agrobacterium tumefaciens
 3.A.8MPTMitochondrial proteins>2,000 (multiple subunits)9 integral membrane constituentsE (mito)2Mitochondrial protein translocase (Tom and Tim) proteins of Saccharomyces cerevisiae
 3.A.9CEPTChloroplast proteins>2,000 (multiple subunits)Several integral membrane constituentsE (chloro)2Chloroplast envelope protein translocase (IAP) proteins of Pisum sativum
 3.A.10H+-PPaseH+660–78015E (plant vacuoles), B, A>10Vacuolar H+-pyrophosphatase (V-PPase) of Arabidopsis thaliana
 3.A.11DNA-TSingle-stranded DNA>1,000 (multiple subunits)3 subunitsB5Competence-related DNA transformation transporter (ComEA-EC-FA) of Bacillus subtilis
3.B.  Decarboxylation-driven active transporters
 3.B.1NaT-DCNa+∼1,000 (3 subunits)11 (β-subunit)B, A10Oxaloacetate decarboxylase of Salmonella typhimurium
3.C.  Methyl transfer-driven active transporters
 3.C.1NaT-MMMNa+∼8 subunits; most integral membrane constituents?A2Na+-transporting methyltetrahydromethanopterin:coenzyme M methyltransferase ofMethanobacterium thermoautotrophicum
3.D.  Oxidoreduction-driven active transporters
 3.D.1NDHH+ or NA+(efflux)14–40 subunitsMultiple integral membrane subunitsB, E (mito, chloro)>10NDH of E. coli
 3.D.2PTHH+ (efflux)∼2,000 (1–3 proteins; 3 domains; dimeric)(12–14)2B, E (mito)>10PTH ofE. coli
 3.D.3QCRH+(efflux)2,000–6,000 multiple (3–11) subunits; dimeric(13)2B, E (mito; chloro)>20Cytochrome bc1 complex ofParacoccus denitrificans
 3.D.4COXH+ (efflux)2,000–6,000 multiple (3–11) subunits; dimeric(12–20)2B, A, E (mito)>20Quinol oxidase (Cyo) of E. coli
 3.D.5Na-NDHNa+(efflux)Multiple subunits?B1Na+-translocating NADH-quinol reductase of Vibrio alginolyticus
 3.D.6NFOH+or Na+ (efflux)Multiple subunits?B∼10H+- or Na+-translocating NADH:ferredoxin oxidoreductase (RnfA–H) of Rhodobacter capsulatus
 3.D.7HHOH+ (efflux)Multiple subunits?A∼5H2:heterodisulfide oxidoreductase of Methanosarcina mazei Göl
 3.D.8FMF-DHH+ or Na+(efflux)Multiple subunits?A∼5Formyl methanofuran dehydrogenase (FwdA-G) of Methanobacterium thermoautotrophicum
3.E.  Light-driven active transporters
 3.E.1FARH+ efflux; Cl uptake∼2507A, E (Y, F)>20Bacteriorhodopsin ofHalobacterium salinarum
 3.E.2PRCH+(efflux)Multiple subunits-B, E (plant chloro)>20Reaction center and cytochromeb6f complex of Rhodobacter sphaeroides
4.A.  Phosphotransferase systems
 4.A.1GlcGlucose; N-acetylglucosamine; α- and β-glucosides∼2,000 (3 domains; dimeric)(8)2B∼30Glucose IICB-IIA ofE. coli
 4.A.2FruFructose; mannitol∼2,000 (3 domains; dimeric)(6)2B∼30Fructose IIB′BC-IIAMH of E. coli
 4.A.3LacLactose; cellobiose; N,N′-diacetylchitobiose∼2,000 (3 domains; dimeric)∼(8)2B∼20Lactose IICB-IIA ofStaphylococcus aureus
 4.A.4GutGlucitol∼2,000 (3 domains; dimeric)(8)2B2Glucitol IICB-IIA ofE. coli
 4.A.5GatGalactitol∼2,000 (3 domains; dimeric)∼(8)2B1Galactitol IIC-IIB-IIA of E. coli
 4.A.6ManGlucose, mannose, fructose, sorbose, etc.∼2,000 (4 domains; probably dimeric)(6(IIC) + 1(IID))2B5Mannose IIAB-IIC-IID of E. coli
9.A.  Transporters of unknown classification
 9.A.1PSTPolysaccharides (export)400–50012B>10Lipopolysaccharide exporter (RfbX1) of E. coli
 9.A.2MerTPHg2+(uptake)∼2002B∼10Mercuric ion transporter (MerTP), encoded on the IncJ plasmid pMERPH of Shewanella putrefaciens
 9.A.3MerCHg2+(uptake)1371B∼10Mercuric ion uptake transporter (MerC), encoded on the IncJ plasmid pMERPH of Shewanella putrefaciens
 9.A.4PnuCNicotinamide mononucleotide (uptake)∼3207B∼10Nicotinamide mononucleotide uptake permease (PnuC) of Salmonella typhimurium
 9.A.5OxalProteins400–6003–5B, E (mito; chloro)∼10Cytochrome oxidase biogenesis protein Oxal of Saccharomyces cerevisiae
 9.A.6INTNucleosides230–2704E (An)∼10Intracellular nucleoside transporter (MTP) of Mus musculus
 9.A.8FeoBFe2+(uptake)∼8008–13B, A∼10Fe2+ uptake transporter (FeoB) of E. coli
 9.A.9FeTFe2+ (Co2+, Cd2+) (uptake)5526E (Y)1Fe2+ transporter (Fet4p) of Saccharomyces cerevisiae
 9.A.10OFeTFe2+(uptake)4046B, A, E∼10Oxidase-dependent Fe2+ transporter (Ftr1p) of Saccharomyces cerevisiae
 9.A.11Ctr1Cu2+(uptake)4062–3E (Y)1Copper transporter (Ctr1p) ofSaccharomyces cerevisiae
 9.A.12Ctr2Cu2+(uptake)160–2003E∼10Copper transporter (Ctr2p) of Saccharomyces cerevisiae
 9.A.13scFATShort-chain fatty acids (uptake)∼47012B, A∼5AtoE of E. coli
 9.A.14NPCRNA; proteins, small molecules, etc.30–50 proteinsENuclear pore complex ofSaccharomyces cerevisiae
 9.A.15AmiShort-chain aliphatic amides; urea (uptake)170–2106B∼5Amide transporter (AmiS) of Pseudomonas aeruginosa
 9.A.16SDTDNA∼8004B>10Septum DNA translocation pore (SpoIIIE) of Bacillus subtilis
 9.A.17MITHeavy-metal ions, Mg2+, Mn2+, Co2+, Ni2+, Fe2+; Al3+; Mn2+200–3602–3B, A, E>50Metal uptake and efflux permease (CorA) of E. coli
 9.A.18PUPPeptides, antibiotics (uptake)4067B2Microbin uptake permease (SbmA) ofE. coli
 9.A.19MgtEMg2+, Co2+ (uptake)310–4704–5B, A10Mg2+ transporter E (MgtE) of Bacillus firmus
 9.A.20LCTMonovalent cations5708–10E (Pl)1Low-affinity cation transporter (LCT1) of Triticum aestivum
  • a Substrates of single transporters within a family are separated by commas; substrates transported by different protein members of the family are separated by semicolons.

  • b Size range (in number of amino acyl residues) when a single type of subunit is present, or for the entire complex when several types of subunits are present.

  • c nTMSs, number of transmembrane α-helical segments in a polypeptide chain. Subscripts refer to the number of polypeptide chains in the complex when known. A subscript nindicates 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. In a few ambiguous cases, the subunit is indicated in parentheses.

  • d Abbreviations: B, bacteria; A, archaea; E, eukaryotes; G− B, gram-negative bacteria; G+ B, gram-positive bacteria; Y, yeasts; F, fungi; Pr, protozoans; Pl, plants; An, animals; mito, mitochondria; chloro, chloroplasts; plastids, nonphotosynthetic plastids of plants; phage, bacteriophages. These abbreviations are used in the tables. Other abbreviations are defined in Table 2 or the text.

  • e See Tables 8 and 9.