<unk>  is an IUBMB approved classification system for membrane transport proteins including ion channels. This classification system was designed to be analogous to the EC number system for classifying enzymes, but it also uses phylogenetic information.
The upper level of classification and some examples of proteins with known 3D structure:
1. Channels/Pores
Voltage-gated ion channel like, including potassium channels KcsA and KvAP, and inward-rectifier potassium ion channel Kirbac 
Large-conductance mechanosensitive channel, MscL 
Small-conductance mechanosensitive ion channel (MscS) 
CorA metal ion<unk> s 
Ligand-gated ion channel of neurotransmitter receptors (acetylcholine receptor) 
Aquaporins 
Chloride channels 
Outer membrane auxiliary proteins (polysaccharide<unk>  
Porins and some other beta barrel proteins of outer membranes
Voltage-gated ion channel like, including potassium channels KcsA and KvAP, and inward-rectifier potassium ion channel Kirbac 
Large-conductance mechanosensitive channel, MscL 
Small-conductance mechanosensitive ion channel (MscS) 
CorA metal ion<unk> s 
Ligand-gated ion channel of neurotransmitter receptors (acetylcholine receptor) 
Aquaporins 
Chloride channels 
Outer membrane auxiliary proteins (polysaccharide<unk>  
Porins and some other beta barrel proteins of outer membranes
2. Electrochemical Potential-driven<unk> s
Mitochondrial carrier proteins 
Major Facilitator Superfamily  (Glycerol-3-hosphate<unk> , Lactose permease, and Multidrug<unk>  EmrD)  
Resistance-nodulation-cell division (multidrug efflux<unk>  AcrB, see multidrug resistance)
Dicarboxylate/amino acid:cation symporter (proton glutamate symporter)  
Monovalent cation/proton antiporter (Sodium/proton antiporter 1 NhaA) 
Neurotransmitter sodium symporter 
Ammonia<unk> s 
Drug/Metabolite<unk>   (small multidrug resistance<unk>  EmrE - the structures  are retracted as erroneous) 
Mitochondrial carrier proteins 
Major Facilitator Superfamily  (Glycerol-3-hosphate<unk> , Lactose permease, and Multidrug<unk>  EmrD)  
Resistance-nodulation-cell division (multidrug efflux<unk>  AcrB, see multidrug resistance)
Dicarboxylate/amino acid:cation symporter (proton glutamate symporter)  
Monovalent cation/proton antiporter (Sodium/proton antiporter 1 NhaA) 
Neurotransmitter sodium symporter 
Ammonia<unk> s 
Drug/Metabolite<unk>   (small multidrug resistance<unk>  EmrE - the structures  are retracted as erroneous) 
3. Primary Active<unk> s
Light absorption-driven<unk> s:
Bacteriorhodopsin-like proteins including rhodopsin (see also opsin)
Bacterial photosynthetic reaction centres and photosystems I and II 
Light harvesting complexes from bacteria and chloroplasts 
Oxidoreduction-driven<unk> s
Transmembrane cytochrome b-like proteins : coenzyme Q - cytochrome c reductase (cytochrome bc1 ); cytochrome b6f  complex; formate dehydrogenase, respiratory nitrate reductase; succinate - coenzyme Q reductase (fumarate reductase); and succinate dehydrogenase.  See electron transport chain.
Cytochrome c oxidases  from bacteria and mitochondria
Electrochemical potential-driven<unk> s
Proton or sodium translocating F-type and V-type ATPases 
P-P-bond hydrolysis-driven<unk> s
P-type calcium ATPase  (five different conformations)  
Calcium ATPase regulators phospholamban and sarcolipin
ABC<unk> s: BtuCD, multidrug<unk> , and  molybdate uptake<unk> 
General secretory pathway (Sec) translocon (preprotein translocase SecY) 
Bacteriorhodopsin-like proteins including rhodopsin (see also opsin)
Bacterial photosynthetic reaction centres and photosystems I and II 
Light harvesting complexes from bacteria and chloroplasts 
Transmembrane cytochrome b-like proteins : coenzyme Q - cytochrome c reductase (cytochrome bc1 ); cytochrome b6f  complex; formate dehydrogenase, respiratory nitrate reductase; succinate - coenzyme Q reductase (fumarate reductase); and succinate dehydrogenase.  See electron transport chain.
Cytochrome c oxidases  from bacteria and mitochondria
Proton or sodium translocating F-type and V-type ATPases 
P-type calcium ATPase  (five different conformations)  
Calcium ATPase regulators phospholamban and sarcolipin
ABC<unk> s: BtuCD, multidrug<unk> , and  molybdate uptake<unk> 
General secretory pathway (Sec) translocon (preprotein translocase SecY) 
4. Group Translocators
5. Transport Electron Carriers
Disulfide bond formation protein B (DsbB) 
Disulfide bond formation protein B (DsbB) 
8. Accessory Factors Involved in Transport
9. Incompletely Characterized Transport Systems
Transporter Classification database
Anatomical Therapeutic Chemical Classification System
Nanosensor
BET theory
Spin quantum number
Genetic marker
Gibbs free energy
Gas diffusion method