Continued from families 4 to 9
Transmembrane channel proteins of this subclass are ubiquitously found in the membranes of all types of organisms, from bacteria to higher eukaryotes. These transporters usually catalyze the movement of solutes by an energy-independent passage through a trans-membrane aqueous pore without evidence for a porter (i.e. carrier)-mediated mechanism. These channel proteins consist largely of a-helical transmembrane segments even if some b-form secondary structure may be present even in the transmembrane channel itself.
| TC no. a | Family | Substrates b | Size range c | Number of transmembrane segmentsd | Distributione | nf | Examples |
| 1.A.1 | VIC | Na+; K+; Ca2+; multiple cations | widely varied | (2)4;(4)2; (6)4; (8)2;(12)2; (24)1; often heterooligomeric | A, B, E | 3 | voltage-gated Na+ channels; voltage-gated Ca2+ channels; K+ channels sensitive to voltage, Ca2+ or cyclic nucleotides of Homo sapiens |
| 1.A.2 | IRK-C | K+ | 350-500 | (2)4 | E (An) | 2 | inward rectifier K+ channels (ATP-activated or G-protein regulated) of Homo sapiens |
| 1.A.3 | RIR-CaC | Ca2+ | 5000 or 2500 | (6)4 | E (An) | 2 | ryanodine receptor Ca2+ channels; inositol-1,4,5-trisphosphate receptor Ca2+ channels of Homo sapiens |
| 1.A.4 | TRP-CC | Ca2+, other cations | 800-1500 | (6)4 | E (An) | 3 | transient receptor potential Ca2+channel, TRP of Drosophila melanogaster |
| 1.A.5 | PCC | Na+, K+, Ca2+ | 4000 | (7-11)n (6)m | E (An) | 1 | polycystins 1 and 2 of Homo sapiens |
| 1.A.6 | ENaC | Na+; cations | 600-700 | (2)4 (a2bg) | E (An) | 2 | epithelial Na+ channels; degenerins; heterooligomeric peptide-gated ionotropic receptors of animals |
| 1.A.7 | ACC | univalent cations, Ca2+ | 350-600 | (2)n | E (An) | 2 | ATP-gated cation channel P2X1 of Homo sapiens |
| 1.A.8 | MIP | H2O; H2O, urea; cations; anions; glycerol, polyols | 80-700 | (6)4 | A, B, E | 3 | aquaporins, Aqp1 of Homo sapiens; glycerol facilitators, GlpF, of Escherichia coli |
| 1.A.9 | LIC | cations or anions | 400-700 | (3-5)5; often heterooligomeric | E (An) | 3 | acetylcholine- or serotonin-activated cation channels; glycine, glutamate or GABA-regulated Cl channels of Homo sapiens |
| 1.A.10 | GIC | univalent cations and Ca2+ | 250-1500 | (3 or 5)5 | B, E (An) | 2 | glutamate-regulated ionotropic channels of Rattus norvegicus |
| 1.A.11 | ClC | Cl-, anions | 400-1000 | 12 | A, B, E | 2 | voltage-gated Cl channel, ClC1 of Homo sapiens |
| 1.A.12 | O-ClC | Cl-, anions | 250-450 | (2)n | E (An) | 2 | organellar voltage-sensitive Cl- channels of Bos taurus |
| 1.A.13 | E-ClC | Cl-, anions | 900 | (4)n | B, E (An) | 1 | Ca2+-activated Cl channel-2 of Homo sapiens |
| 1.A.14 | NSCC1 | Na+, Li+, K+ | c. 450 | (4)n | E (An) | 0 | nonselective cation channel, NSC1 of Mus musculus |
| 1.A.15 | NSCC2 | Na+, K+, Cs+; slowly Ca2+ | 250-400 | (2)n | E (An, F) | 1 | nonspecific channel translocationprotein-1 NS1, of Homo sapiens; Sec62 of Saccharomyces cerevisiae |
| 1.A.16 | Mid1 | Ca2+ | 450-550 | 1 or 2 | E (Y) | 1 | Mid1 of Saccharomyces cerevisiae |
| 1.A.17 | CSC | ions, solutes | 150-200 | b-structure? | E (Pl) | 1 | chloroplast outer envelope solute channel, CSC of Pisum sativum |
| 1.A.18 | Tic110 | anions, proteins | 1000 | 2 | E (Pl) | 1 | protein-import-related anion-selective channel, Tic110 of Pisum sativum |
| 1.A.19 | M2-C | H+ | c. 100 | (1)4 | V | 0 | matrix protein, M2 of influenza virus |
| 1.A.20 | CybB | H+ | 450-750 | 6 heterooligomeric | E (An, Pl) | 2 | gp91phox phagocyte NADPH oxidase-associated cytochrome b558 H+ channel of Homo sapiens |
| 1.A.21 | Bcl-2 | protein (cyt c) | 100-350 | (1-5)n (n=2?) | E (An), V | 2 | apoptosis regulator, Bcl-X(L) of Homo sapiens |
| 1.A.22 | MscL | proteins, ions (slightly cation- selective) | 100-200 | (2)5 | B | 1 | large mechanosensitive ion channels, MscL of E.coli |
| 1.A.23 | MscS | ions (slightly anion-selective) | 200-1150 | 3-14 | A, B, E | 2 | small-conductance mechanosensitiveion channel, KefA of Escherichia coli |
| 1.A.24 | Connexin | smallmolecules(no discrimination) | 200-600 | (4)n | E (An) | 2 | vertebrate connexin 43 (gap junction-1 protein) of Rattus norvegicus |
| 1.A.25 | Innexin | smallmolecules(no discrimination) | 300-600 | (4)n | E (An) | 2 | invertebrate innexin UNC-7 of Caenorhabditis elegans |
| 1.A.26 | PPD | small molecules | c. 300 | 1 | E(Pl) | 1 | gap junction protein CX32 of Arabidopsis thaliana |
| 1.A.27 | PLM | Cl- (anion-selective), taurine, lactate, glutamate, isethionate, gluconate | 80-100 | (1)n | E (An) | 1 | phospholemman; Cl- conductance inducer protein Mat-8 of Mus musculus |
| 1.A.28 | UT | urea, water | 350-400 | 10 | E (An) | 1 | kidney vasopressin-regulated urea transporter UT2 of Rattus norvegicus |
| 1.A.29 | UAC | urea, amides | 150-250 | 6 | B | 1 | UreI protein of Helicobacter pylori |
| 1.A.30 | Mot/Exb | ||||||
| 1.A.30.1 | Mot | H+; Na+ | 200-350 (MotA)200-500 (MotB) | 41 | B | 2 | MotA and MotB proteins of Escherichia coli |
| 1.A.30.2 | Exb | H+ (energy-transducing system) | 150-400+150- 350+100-200 (TonB ExbBD) 350-450+200- 300+100-200 (TolAQR) | 1+3+1 1+3+1 | B(G-) | 2 | TonB/ExbB/ExbD of Escherichia coli |
| 1.A.31 | Annexin | ions | 250-700 | 4, 8 | E | 2 | Hydra annexin XII |
| 1.A.32 | NB-C | ions | c. 100 | 1 | V | 0 | NB protein of influenza B virus |
| 1.A.33 | Hsp70 | ions, polypeptides | 500-750 | 0-2 | A,B,E | 3 | Hsp70 protein of Arabidopsis thaliana |
| 1.A.34 | EVE1-C | RNA | 1200-1300 | 5 | V | 1 | herpes simplex structural polyprotein |
| 1.A.35 | MIT | heavy metal ions | 300-400 | 2-3 | B | 2 | CorA protein of Escherichia coli |
| 1.A.36 | ICC | anions | 500-600 | 4 | E | 0 | MCLC protein of Homo sapiens |
These proteins form transmembrane pores that usually allow the energy-independent passage of solutes across a membrane. The transmembrane portions of these proteins consist exclusively of b-strands that usually form b-barrels. Porins are found in the outer membranes of Gram-negative bacteria, mitochondria, chloroplasts and possibly of acid-fast Gram-positive bacteria.
| TC no. a | Family | Substrates b | Size range c | Number of transmembrane segmentsd | Distributione | nf | Examples |
| 1.B.1 | GBP | ions, small molecules | 250-450 | 16-stranded antiparallel b-barrels | B(G-),V | 2 | OmpF of Escherichia coli |
| 1.B.2 | CP | ions, small molecules | 300-400 | B | 1 | Omp1 of Chlamydia psittaci | |
| 1.B.3 | SP | sugars | 250-550 | 18-stranded antiparallel b-barrels | B | 1 | LamB of Escherichia coli |
| 1.B.4 | BRP | ions, small molecules | 300-400 | B | 1 | Omp2 of Brucella abortus | |
| 1.B.5 | POP | ions, small molecules | 400-450 | B | 1 | OprP of Pseudomonas aeruginosa | |
| 1.B.6 | OOP | ions, small molecules | 350-450 | 8 b-strands | B | 2 | OmpA of Escherichia coli |
| 1.B.7 | RPP | ions, small molecules | 250-350 | 16-stranded b-barrels | B | 0 | PorCa porin of Rhodobacter capsulatus |
| 1.B.8 | MPP | anions, small proteins | 250-350 | 1 a-helix and 12 or 13 b-strands | E | 2 | E2 mitochondrial outer membrane VDAC of Saccharomyces cerevisiae |
| 1.B.9 | FadL | fatty acids | 400-500 | B | 1 | FadL of Escherichia coli | |
| 1.B.10 | Tsx | nucleosides | 250-300 | 14-stranded b-barrels | B | 1 | Tsx of Escherichia coli |
| 1.B.11 | FUP | fimbrial protein | 750-950 | 24 b-strands | B | 2 | FacD of Escherichia coli |
| 1.B.12 | AT | N-terminal protein domains | 250-300 | 14 b-strands | B(G-) | 2 | AidA of Escherichia coli |
| 1.B.13 | AEP | alginate | c. 500 | 18 b-strands | B(G-) | 0 | AlgE of Pseudomonas aeruginosa |
| 1.B.14 | OMR | iron-chelate complexes, colicins, vitamin B12, etc. | 350-1100 | 22 antiparallel b-strands | B(G-) | 2 | FepA of Escherichia coli |
| 1.B.15 | RafY | small molecules, oligosaccharides | 450-500 | B(G-) | 1 | RafY of Escherichia coli | |
| 1.B.16 | SAP | short-chain amides, small molecules | c. 400 | B(G-) | FmdC of Methylophilus methylotrophus | ||
| 1.B.17 | OMF | proteins; lipooligosaccharides; drugs, dyes, signaling molecules; heavy-metal ions; etc. (some OMFs can accommodate multiple substrate types) | 400-550 | (4)3 -strands | B(G-) | 2 | TolC of Escherichia coli |
| 1.B.18 | OMA | complex carbohydrates | 350-600 | B(G-) | 2 | ExoF of Rhizobium meliloti | |
| 1.B.19 | OprB | ions; small molecules | 400-500 | B(G-) | 1 | OprB of Pseudomonas aeruginosa | |
| 1.B.20 | TPS | proteins | 550-600 | B(G-) | 2 | ShlB of Serratia marcescens | |
| 1.B.21 | OmpG | ions, small molecules | c. 300 | 16 | B(G-) | OmpG of Escherichia coli | |
| 1.B.22 | Secretin | proteins | 400-800 | (x)12 | B, V | PulD of Klebsiella oxytoca | |
| 1.B.23 | CBP | ions, small molecules | 400-950 | 14-16 | B(G-) | 1 | SomA of Synechococcus sp |
| 1.B.24 | MBP | ions, small molecules | 200-250 | MspA of Mycobacterium smegmatis | |||
| 1.B.25 | Opr | ions, small molecules | c. 450 | B(G-) | 0 | OprD2 of Pseudomonas aeruginosa | |
| 1.B.26 | CDP | cyclodextrins | c. 350 | B(G-) | 0 | CymA of Klebsiella oxytoca | |
| 1.B.27 | HOP | ions, small molecules | 200-600 | 18 | B(G-) | 1 | HopE of Helicobacter pylori |
| 1.B.28 | OEP24 | ions, small molecules | c. 200 | 7 | E(P) | 1 | OEP24 of Pisum sativum |
| 1.B.29 | OEP21 | organic anions | c. 200 | E(P) | 1 | OEP21 of Pisum sativum | |
| 1.B.30 | OEP16 | organic cations | c. 150 | (2 b, 1 a)4 | E(P) | 1 | OEP16 of Pisum sativum |
| 1.B.31 | MomP | ions, small molecules | c. 400 | B(G-) | 1 | MomP of Campylobacter jejuni | |
| 1.B.32 | FomP | ions, small molecules | c. 400 | (16)3 | B(G-) | 0 | FomA of Fusobacterium nucleatum |
| 1.B.33 | VC/NP | acetylated chitooligomers; ions, small molecules | 300-400 | B(G-) | 1 | ChiP of Vibrio furnissii | |
| 1.B.34 | PorA | ions, small molecules | c. 50 | B | 0 | PorA of Corynebacterium glutamicum |
These proteins and peptides are synthesized by one cell and secreted for insertion into the membrane of another cell where they form transmembrane pores. They may exert their toxic effects by allowing the free flow of electrolytes and other small molecules across the membrane, or they may allow entry into the target cell cytoplasm of a toxin protein that ultimately kills or controls the cell. Both ribosomally synthesized large protein and small peptide toxins are included in this category.
| TC no. a | Family | Substrates b | Size range c | Number of transmembrane segmentsd | Distributione | nf | Examples |
| 1.C.1 | Colicin | ions, small molecules | 400-700 (150-180 for the channel domain) | 2 | B | 2 | colicin Ia of E.coli |
| 1.C.2 | ICP | ions, small molecules | 600-1400 | 6 | B | 2 | CryIAa of Bacillus thuringiensis |
| 1.C.3 | aHL | ions, small molecules | 300-350 | (2)2b-strands | a-hemolysin of Staphylococcus aureus | ||
| 1.C.4 | Aerolysin | ions, small molecules | 450-500 | (2)2b-strands | B, E (Pl) | 1 | aerolysin of Aeromonas hydrophila |
| 1.C.5 | e-toxin | K+; ions, small molecules | c. 350 | 1 | B | 1 | b-toxin of Clostridium perfringens |
| 1.C.6 | YKT-K1 | cations, ATP, small molecules | c. 300 | [2(a-subunit) + 1(b-subunit)]n | E | 0 | yeast killer toxin of Saccharomyces cerevisiae |
| 1.C.7 | DT | DT, A-chain (protein) | 550-600 | (2)n n = variable | Bp | 0 | diphtheria toxin (DT) of corynebacteriophage |
| 1.C.8 | BTT | BTT, L-chains | 1150-1350 | (2)n | B | 1 | botulinum and tetanus toxin channels of Clostridium species |
| 1.C.9 | VacA | ions, small molecules | 1250-1350 | (3)n | B | 0 | VacA of Helicobacter pylori |
| 1.C.10 | HlyE | ions (moderately cation-selective) | c. 300 | (2)n | B | 0 | HlyE of Escherichia coli |
| 1.C.11 | RTX-toxin | ions, small molecules | 250-1850 | (3)n | B | 2 | HlyA of Escherichia coli |
| 1.C.12 | TAC | ions, metabolites, proteins | 450-600 | (2 b-hairpins)n n=30-60 | B | 2 | perfringolysin O of Clostridium perfringens |
| 1.C.13 | Ctx | ions | c. 300 | (?)5? | Bp | 0 | leucocidin cytotoxin Ctx of Pseudomonas aeruginosa phage jCTX |
| 1.C.14 | CHL | ions and other solutes | 450-750 | (0-1)5? | B | 1 | HlyA of Vibrio cholerae |
| 1.C.15 | WSP | small molecules | c. 400 | (0)n | E(An) | 0 | whipworm stichosome porin of Trichuris trichiura |
| 1.C.16 | Magainin | small solutes, electrolytes, water | 80-300 | (2)n | E(An) | 1 | magainin precursor of Xenopus laevis |
| 1.C.17 | Cecropin | small solutes, electrolytes, water | 30-65 | (0-1)n | E(An) | 2 | cecropin A, B and C precursor of Hyalophora cecropia |
| 1.C.18 | Melittin | small solutes, | 25-70 | (0-2)n | E(An) | 0 | melittin major precursor of electrolytes, water Apis mellifera |
| 1.C.19 | Defensin | small solutes, electrolytes, water | 30-100 | (0)n | E(A) | 2 | neutrophil defensin GP-CS1 of Cavia porcellus |
| 1.C.20 | Nisin | small solutes, electrolytes, water | 55-60 | (0)n | B(G+) | 1 | nisin precursor of Lactococcus lactis |
| 1.C.21 | Lacticin 481 | small solutes, electrolytes, water | c. 50 | (0)n | B(G+) | 1 | lacticin 481 of Lactococcus lactis |
| 1.C.22 | Lactococcin A | small solutes, electrolytes, water | 65-75 | (0-1)n | B(G+) | lactococcin A precursor of Lactococcus lactis | |
| 1.C.23 | Lactocin S | small solutes, electrolytes, water | 25 | (1)n | B(G+) | 0 | lactocin S of Lactobacillus sake L45 |
| 1.C.24 | Pediocin | small solutes, electrolytes, water | 40-70 | (0)n | B(G+) | 1 | pediocin PA-1 precursor of Pediococcus acidilactic |
| 1.C.25 | Lactococcin G | small solutes, electrolytes, water | c. 40+35 | (0)n | B(G+) | 0 | lactococcin G of Lactococcus lactis |
| 1.C.26 | Lactacin X | small solutes, electrolytes, water | c. 75 + 65 | (2)n | B(G+) | 0 | LafA and LafX of Lactobacillus johnsonii |
| 1.C.27 | Divergicin A | small solutes, electrolytes, water | c. 75 | (2)n | B(G+) | 0 | DvnA of Carnobacterium divergens |
| 1.C.28 | AS-48 | small solutes, electrolytes, water | c. 100 | (1)n | B(G+) | 0 | AS-48 of Enterococcus faecalis S-48 plasmid pMB2 |
| 1.C.29 | Plantaricin EF | small solutes, electrolytes, water | c. 55+50 | (0)n | B(G+) | 0 | PlnE, F of Lactobacillus plantarum |
| 1.C.30 | Plantaricin JK | small solutes, electrolytes, water | c. 55 + 55 | (0)n | B(G+) | 0 | PlnJ, K of Lactobacillus plantarum |
| 1.C.31 | Colicin V | ions, small molecules | c. 100 | (1-2)n | B | 0 | colicin V of Escherichia coli |
| 1.C.32 | Mastoparan | small molecules | c. 15 | barrel stove (1)n | E (An) | 1 | mastoparan of Vespa xanthoptera |
| 1.C.33 | Cathilicidin | small molecules | 90-250 | (1)n | E (An) | 2 | pre-myeloid cathilicidin 1 of Equus caballus |
| 1.C.34 | Tachyplesin | small molecules | c. 80 | (1)n | E (An) | 1 | tachyplesin I of Tachyplesus tridentatus |
| 1.C.35 | Amoebapore | small molecules | c. 100 | (1)n | E (Pr) | 1 | amoebapore of Entamoeba histolytica |
| 1.C.36 | IIITCP | proteins | 300-600 | (2)n | B | 1 | type III-protein secretion target cell pore protein, YopB of Yersinia pseudotuberculosis |
| 1.C.37 | Lactococcin 972 | small molecules | 50-100 | (1)n | B | 0 | lactococcin 972 of Lactococcus lactis |
| 1.C.38 | Equinatoxin | small molecules | 150-250 | (1)3 or (1)4 | E (An) | 2 | equinatoxin of Actinia tenebrosa |
| 1.C.39 | CPC9 | ions, small solutes | 500-600 | (1)n | E(An) | 2 | C9 of Equus caballus |
| 1.C.40 | BPIP | cholesterol, lipopolysaccharide | 250-500 | (1)n | E(An) | 2 | BPIP precursor of Homo sapiens |
| 1.C.41 | HBL | ions, small solutes | 150-400 | (2)n | B | 1 | hemolysin YhlA of Edwardsiella tarda |
| 1.C.42 | BAPA | protein toxin, small molecules | 150-800 | [3 (b?)]n | B(G+) | 0 | iotatoxin Ib of Clostridium perfringens |
| 1.C.43 | Lysenin | various solutes | c. 300 | (1)n | E(An) | 0 | lysenin of Eisenia foetida |
| 1.C.44 | PT | small molecules | 45-47 (precursors: 70-140) | two antiparallel a-helices and two antiparallel b-strands | E(Pl) | viscotoxin B precursor of Viscum album | |
| 1.C.45 | PD | small molecules | 45-54 (precursors: 80-120) | triple-stranded antiparallel b-sheets and 1 a-helix | E(Pl) | 2 | g-thionin of Nicotiana tabacum |
| 1.C.46 | CNP | cations | small peptides (precursors: 80-140) | (0)n | E(An) | 2 | C-type natriuretic peptide precursor of Homo sapiens |
| 1.C.47 | Insect defensin | ions | small peptides (precursors: 80-120) | (0-2)n | E(An) | phormicin precursor of Protophormia terranovae | |
| 1.C.48 | PPF | ions | 200-300 | 1-3 | E(An) | 2 | major prion protein precursor Prp of Ovis aries |
| 1.C.49 | Amylin | ions | 25-150 | 0-1 | E(An) | 2 | amylin of Canis familiaris |
| 1.C.50 | APP | ions | 50-900 | 0-2 | E(An) | 2 | amyloid b-protein peptide of Rattus norvegicus |
| 1.C.51 | Pilosulin | ions | c. 100 | 1 | E(An) | 1 | philosin I of Myrmecia pilosula |
| 1.C.52 | Dermaseptin | ions | 70-80 | 1 | E(An) | 1 | brevinin-2EF of Rana esculenta |
| 1.C.53 | Bacteriocin AS-48 | ions and small molecules | 70 (cyclic) (precursors: 105) | 1 | B(G+) | 0 | bacteriocin AS-48 of Enterococcus faecalis |
| 1.C.54 | ST-B | shiga toxin A | (89)5 | 1-2 | Bp | 1 | verotoxin B-chain of Escherichia coli |
| 1.C.55 | VirE2 | proteins, DNA, anions | 500-600 | b-structure (b-barrel?) | B | 1 | VirE2 of Agrobacterium tumefaciens |
| 1.C.56 | HrpZ | cations, small molecules | c. 350 | (2)n | B | 0 | HrpZ cation-selective channel protein of Pseudomonas syringae |
| 1.C.57 | CCT | toxin domain, ions, other solutes | 2100-3200 | 2 | B | 0 | cytotoxin B of Clostridium difficile |
| 1.C.58 | Microcin E492 | univalent cations | c. 100 | (0)n | B | 0 | microcin C24 of Escherichia coli |
These molecules, often chains of L- and D-amino acids and of the hydroxy acids lactate and b-hydroxybutyrate, form oligomeric trans-membrane channels. Voltage may induce channel formation by promoting assembly of the oligomeric pore-forming structure. These "depsipeptides" are often made by bacteria and fungi and are used as agents of biological warfare. Other substances, completely lacking amino acids, may also be involved in channel formation.
| TC no. a | Family | Substrates b | Size range c | Number of transmembrane segmentsd | Distributione | nf | Examples |
| 1.D.1 | Gramicidin A | univalent cations | 15 L- and D-amino acids | 0.5 | B | 0 | gramicidin A Bacillus brevis |
| 1.D.2 | Syringomycin | cations | cyclic lipodepsipeptide containing nonprotein amino acids | 1? | B | 1 | syringomycin of Pseudomonas syringae |
| 1.D.3 | Syringopeptin | cations | cyclic lipodepsipeptide containing nonprotein amino acids | 1? | B | 1 | syringopeptin SP22 of Pseudomonas syringae |
| 1.D.4 | Tolaasin | cations | lipodepsipeptide (contains D-amino acids, hydroxy acids, and fatty acids) | 1? | B | 1 | tolaasin of Pseudomonas tolaasii |
| 1.D.5 | Alamethicin | ions | 20-21 amino acids including nonprotein amino acids | 1? | E(Fu) | 1 | longibrachin I of Trichoderma longibranchiatum |
| 1.D.6 | cPHB-CC | DNA uptake | PHB, Ca2+ and polyphosphate | - | B | 1 | poly-(R)-3-hydroxybutyrate channel of Streptomyces lividans |
| 1.D.7 | Beticolin | ions | mostly naphthocycloheptaxanthene acetates, c. 640 Da | - | E(Fu) | 1 | beticolin 0 of Cercospora beticola |
| 1.D.8 | Saponin | various solutes | glycosylated triterpenoids, steroids and alkaloids | - | E(Pl) | 0 | avenacoside A of Avena sativa |
| 1.D.9 | PG-IC | ions | polyglutamine ion channel, about 60 amino acid residues | - | E(An) | 1 | polyglutamine of Homo sapiens |
| 1.D.10 | Ceramide | small proteins | lipids | - | E(An) | 1 | C2-ceramide of Glycine max |
| 1.D.11 | PEA | mainly K+, also organic compounds | no amino acids, c. 920 Da | - | B | 1 | amphotericin B of Streptomyces nodosus |
| 1.D.12 | TyrA | various solutes | 8-12 amino acids | - | B | 1 | surfactin of Bacillus subtilis |
This subclass comprises integral membrane proteins that control the access of phage-encoded cell-wall-lysing enzymes, the endolysins, by rapid formation of a homo-oligomeric lesion in the membrane. The presence of a holin and of endolysin is essential for bacteriophage-induced bacterial lysis. Some holins are encoded within bacterial genomes and probably promote programmed cell death. The holins are an extremely diverse functional group and are given here the status of a subclass.
| TC no. a | Family | Substrates b | Size range c | Number of transmembrane segmentsd | Distributione | nf | Examples |
| 1.E.1 | P21 holin | endolysin, ions, small metabolites | 70-100 | 2 | B, Bp | 1 | lysis protein S of Escherichia coli |
| 1.E.2 | b holin | endolysin | 100-150 | 3 | B, Bp | 1 | lysis protein S of phage b |
| 1.E.3 | P2 holin | endolysin | 90-100 | 3 | Bp | 1 | lysis protein TM of phage P2 |
| 1.E.4 | LydA holin | endolysin | c. 110 | 2 | B, Bp | 0 | LydA protein of Escherichia coli |
| 1.E.5 | PRD1 holin | endolysin | 90 | 1 | Bp | 0 | protein M of phage PRD1 |
| 1.E.6 | T7 holin | endolysin | 45-70 | 1 | Bp | 1 | Gb 17.5 Phage T7 |
| 1.E.7 | HP1 holin | endolysin | 70-90 | 1 | B, Bp | 1 | holin of Haemophilus influenzae phage HP1 |
| 1.E.8 | T4 holin | endolysin | 200-250 | 1 | Bp | 1 | lysis protein of phage T4 |
| 1.E.9 | T4 Immunity | endolysin | c. 80 | 2 | Bp | 1 | immunity protein of phage T4 holin |
| 1.E.10 | f29 holin | protein | 100-150 | 2 | Bp | 1 | GP14 of Bacillus phage Phi 29 |
| 1.E.11 | f11 holin | endolysin | 50-200 | 2 | Bp | 0 | holin of Staphylococcus phage Phi11 |
| 1.E.12 | fAdh holin | endolysin | 114 | 1 | Bp | 0 | holin of Lactobacillus gasseri phage Phi Adh |
| 1.E.13 | fU53 holin | endolysin | c. 66 | 1 | Bp | 0 | holin of Lactococcus lactis phage U53 |
| 1.E.14 | LrgA holin | endolysin | 100-150 | 4 | B | 1 | LrgA of Staphylococcus aureus |
| 1.E.15 | ArpQ holin | endolysin | c. 60 | 2 | B | 0 | ArpQ of Enterococcus hirae |
| 1.E.16 | Cph1 holin | endolysin | c. 135 | 3 | Bp | 0 | Cph1 holin of Streptococcus pneumoniae phage Cp-1 |
| 1.E.17 | BlyA holin | endolysin | c. 70 | 1 | Bp | 0 | BlyA of cp32 prophage from Borrelia burgdorferi |
| 1.E.18 | R1t holin | lysin | 75-80 | 2 | Bp | 0 | Orf49 holin of L. lactis phage r1t |
| 1.E.19 | TcdE holin | toxin | c. 160 | 3 | B | 0 | TcdE of Clostridium difficile |
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.