Membrane transport proteins, or transporters, are proteins
- across the lipid layer on a cell membrane
- forming a channel with hydrophilic amino acid side chains
- involved in the transportation of small molecules such as ions, and large molecules such as proteins across the cellular membrane
- involved in various physiological processes, e.g., nutrient uptake, waste removal, and oxygen transport
- having conformational changes during the solute translocation
- are targets of about 30% of drugs
Different types of membrane transporters:
- Uniporters: mediate the unidirectional translocation of a substrate
- Antiporters: two substrates are transported in opposite directions in a coupled process
- Symporters: the co-transport of two separate substrates in the same direction
Classes of membrane transporters (by energetics):
- Passive transporters: ion channels, e.g., the Na+ channel; facilitated diffusion, e.g., glucose transporter
- Primary active transporters: use ATP, light, or substrate oxidation as energy resources, e.g., H+-ATPase
- Secondary active transporters: use ion gradients as energy sources, e.g., Na+/amino acid symporters
2nd and 3rd basis of transporter classification:
- Phylogenetic grouping
- Substrate specificity and polarity
