An organic cation transport protein mediates the transport of organic cations across the cell membrane. These proteins are members of the solute carrier family, subfamily 22. This family of proteins can also transport zwitterions and anions, though it is a different subfamily of solute carrier proteins than the organic anion transporters.
Function Organic cation transport proteins (OCTs) are involved in membrane transport through facilitated diffusion of organic cations and some weak bases. They are crucial for the disposal of many organic cations that come from drugs or other environmental sources. They also allow for the recycling of necessary organic cations. Some of these organic cation transport proteins are compound-specific, and others transport a broad range of cations across the membrane. For example, the disposing of the blood sugar medication Metformin is dependent on organic cation transport proteins.
Structure The general structure of an OCT or OCTN consists of 11-12 alpha-helical transmembrane protein domains. These create a transmembrane unit that creates loops on both sides of the membrane. There is typically a large extracellular loop with glycosylation sites at the beginning of the transporter, followed by many smaller loops that connect the transmembrane protein domains on the extracellular side. The loops found on the inside of the cell contain many sites for phosphorylation. There is also an intracellular loop between the transmembrane domains 6 and 7 that contains phosphorylation sites that are believed to contribute to regulation of activity of the organic cation transport protein. Some of these phosphorylation sites are shared between the different organic cation transport proteins.
Nomenclature The various types of organic cation transport proteins are often referred to in its respective abbreviated form or by the gene that codes it. For example, OCT1 is coded by the SLC22A1 gene. Similarly, OCT2 is often called SLC22A2.
Proteins AbbreviationProtein nameLocationTransported solute(s)Associated disorder(s)SLC22A1Solute carrier family 22 member 1Liver, brain (cerebellum) SLC22A2Solute carrier family 22 member 2Primarily in kidney, also in brain SLC22A3Solute carrier family 22 member 3Brain and kidney Histamine, dopamine, serotonin, norepinephrine, MPP+ SLC22A4Solute carrier family 22 member 4 Sodium ion and ergothioneine SLC22A5Solute carrier family 22 member 5 Primary carnitine deficiencySLC22A6Solute carrier family 22 member 6 SLC22A7Solute carrier family 22 member 7 SLC22A8Solute carrier family 22 member 8 SLC22A9Solute carrier family 22 member 9 SLC22A10Solute carrier family 22 member 10 SLC22A11Solute carrier family 22 member 11 SLC22A12Solute carrier family 22 member 12KidneyUric acidHyperuricemia and hypouricemiaSLC22A13Solute carrier family 22 member 13 SLC22A14Solute carrier family 22 member 14 SLC22A15Solute carrier family 22 member 15 SLC22A16Solute carrier family 22 member 16 SLC22A17Solute carrier family 22 member 17 SLC22A18Solute carrier family 22 member 18 Beckwith-Wiedemann syndrome, Wilms tumor, rhabdomyosarcoma, adrenocortical carcinoma, and lung, ovarian, and breast cancerSLC22A19Solute carrier family 22 member 19 SLC22A20Solute carrier family 22 member 20
References
Koepsell, H., Endou, H. The SLC22 drug transporter family. Pflugers Arch - Eur J Physiol 447, 666–676 (2004). https://doi-org.byu.idm.oclc.org/10.1007/s00424-003-1089-9 Ciarimboli, G., Schlatter, E. Regulation of organic cation transport. Pflugers Arch - Eur J Physiol 449, 423–441 (2005). https://doi-org.byu.idm.oclc.org/10.1007/s00424-004-1355-5 Kerb, R., Brinkmann, U., Chatskaia, N., Gorbunov, D., Gorboulev, V., Mornhinweg, E., Keil, A., Eichelbaum, M. & Koepsell, H. (2002). Identification of genetic variations of the human organic cation transporter hOCT1 and their functional consequences. Pharmacogenetics, 12 (8), 591-595.