TABLE 7.
Classification of channel proteins (excluding porins) according to substrate specificity
| Substrate | TC no. | Family | Source | Regulation |
|---|---|---|---|---|
| I.A. Nonselective | ||||
| Nonselective | 1.A.17 | CSC | Pl | |
| Nonselective (slight cation-over-anion selectivity) | 1.A.22 | MscL | B | Mechanosensitive (osmotic pressure) |
| Nonselective (slight anion-over-cation selectivity) | 1.A.23 | MscS | B | Mechanosensitive (osmotic pressure) |
| Nonselective | 1.A.24 | Connexin | An | |
| Nonselective | 1.A.25 | Innexin | An | |
| Nonselective | 1.A.28–1.A.43 | Holin | B, phage | |
| Nonselective | 1.C | All toxin-type pore-forming proteins/peptides | B, A, E | |
| I.B. Water | ||||
| Water | 1.A.8 | MIP aquaporins | B, E | Hormonal regulation in animals |
| Water | 1.A.44 | UT | An | |
| I.C. Cations | ||||
| Cation selective | 1.A.1.11 | VIC | An | Voltage sensitive |
| Cation selective | 1.A.3.1 | RIR-CaC | An | Ryanodine sensitive |
| Cation selective | 1.A.3.2 | RIR-CaC | An | Inositol triphosphate sensitive |
| Cation selective | 1.A.4 | TRP-CC | An | Responsive to pain, heat, etc. |
| Cation selective | 1.A.5 | PCC | An | Ca2+ activated |
| Cation selective | 1.A.6.1.2 | ENaC | An | Proton gated |
| Cation selective | 1.A.6.2.1 | ENaC | An | |
| Cation selective | 1.A.7 | ACC | An | Exogenous-ATP sensitive |
| Cation selective | 1.A.9.1 | LIC | An | Acetylcholine activated |
| Cation selective | 1.A.9.2 | LIC | An | Serotonin activated |
| Cation selective | 1.A.10.1.3 | GIC | An | Exogenous-glutamate sensitive |
| Cation selective | 1.A.13 | Gramicidin | B | |
| Cation selective | 1.A.14 | NSCC1 | An | |
| Cation selective | 1.A.15 | NSCC2 | E (Y, F, An) | |
| Cation selective | 1.A.16 | Mid1 | Y | Stretch activated |
| Cation selective | 1.A.26 | SAT | Pl | |
| H+ | 1.A.19 | IVC | An (virus) | |
| H+ | 1.A.20 | CybB | An, Pl | Arachidonate |
| H+ | 1.A.45 | Mot | B | |
| K+ | 1.A.1.1–9 | VIC | B, A, Y, An, Pl | Voltage sensitive; Ca2+ activated; cyclic nucleotide gated |
| K+ | 1.A.2 | IRK-C | An | ATP regulated; G protein regulated; voltage sensitive |
| Na+ | 1.A.1.10 | VIC | An | Voltage sensitive |
| Na+ | 1.A.6.1.1 | ENaC | An | Ligand regulated |
| Na+ | 1.A.6.3.1 | ENaC | An | Peptide ligand regulated |
| Na+ | 1.A.45 | Mot | B | |
| Na+, K+, (Ca2+) selective | 1.A.10 | GIC | An | Glutamate gated |
| NH4+ | 1.A.26 | SAT | Pl | |
| I.D. Anions | ||||
| Cl− | 1.A.9.3 | LIC | An | Glycine inhibited |
| Cl− | 1.A.9.4 | LIC | An | Glutamate inhibited |
| Cl− | 1.A.9.5 | LIC | An | γ-Aminobutyrate inhibited |
| Cl− | 1.A.12 | O-ClC | An | Voltage regulated |
| Cl− | 1.A.13 | E-ClC | An; B? | Ca2+-calmodulin kinase regulated |
| Cl− (anion selective) | 1.A.11 | ClC | B, A, E | Voltage regulated |
| Cl− (anion selective) | 1.A.16 | Tic110 | Pl | |
| Cl− (anion selective) | 1.A.27 | PLM | An | Hyperpolarization activated |
| II.A. Sugars and polyols | ||||
| Glycerol | 1.A.8 | MIP-glycerol | B, E | Glycerol inducible in bacteria |
| Propanediol | 1.A.8 | MIP-glycerol | B, E | Glycerol inducible in bacteria |
| II.B. Monocarboxylates | ||||
| Organic anions | 1.A.27 | PLM | An | Hyperpolarization activated |
| Gluconate | 1.A.27 | PLM | An | Hyperpolarization activated |
| Glutamate | 1.A.27 | PLM | An | Hyperpolarization activated |
| Isethionate | 1.A.27 | PLM | An | Hyperpolarization activated |
| Lactate | 1.A.27 | PLM | An | Hyperpolarization activated |
| Taurine | 1.A.27 | PLM | An | Hyperpolarization activated |
| III.B. Amines, amides, and polyamines | ||||
| Methylammonium | 1.A.26 | SAT | Pl | |
| Urea | 1.A.8 | MIP | B | |
| Urea | 1.A.44 | UT | An | |
| VII.B. Proteins | ||||
| Autolysins | 1.A.28–1.A.43 | Holin | B, phage | |
| Botulinum toxin, L-chaina | 1.C.8.1.1 | BTT | B | |
| Cytochrome c | 1.A.21 | Bcl-2 | An | |
| Diphtheria toxin, A-chaina | 1.C.7.1.1 | DT | B | |
| Nucleases | 1.A.34.3 | Holin | B | |
| Proteins | 1.A.18 | Tic110 | Pl | |
| Tetanus toxin, L-chaina | 1.C.8.1.2 | BTT | B | |
| Thioredoxin | 1.A.22.1.1 | MscL | B | Osmotic downshift |
a
These toxins in TC category 1.C function to import proteins into the host cell.