Slco2b1
Domain
A conserved histidine residue in the third transmembrane domain (His-128) might play an essential role in the pH sensitivity of SLCO2B1/OATP2B1-mediated substrate transport. Transmembrane domain 1 (TM1) may be localized within the substrate binding pocket.
Function
Mediates the Na(+)-independent transport of steroid sulfate conjugates such as estrone 3-sulfate (E1S), dehydroepiandrosterone sulfate (DHEA-S) and pregnenolone sulfate (PregS) and other specific organic anions (PubMed:31123035). Responsible for the transport of E1S through the basal membrane of syncytiotrophoblast, highlighting a potential role in the placental absorption of fetal-derived sulfated steroids including DHEA-S (By similarity). Also facilitates the uptake of sulfated steroids at the basal/sinusoidal membrane of hepatocytes, therefore accounting for the major part of organic anions clearance of liver. Mediates the intestinal uptake of sulfated steroids. Mediates the uptake of the neurosteroids DHEA-S and PregS into the endothelial cells of the blood-brain barrier as the first step to enter the brain. Also plays a role in the reuptake of neuropeptides such as substance P/TAC1 and vasoactive intestinal peptide/VIP released from retinal neurons. May act as a heme transporter that promotes cellular iron availability. Also transports heme by-product coproporphyrin III (CPIII), and may be involved in their hepatic disposition (By similarity). Mediates the uptake of other substrates such as prostaglandins D2 (PGD2), E1 (PGE1) and E2 (PGE2), taurocholate, L-thyroxine, leukotriene C4 and thromboxane B2 (PubMed:31123035). May contribute to regulate the transport of organic compounds in testis across the blood-testis-barrier (By similarity). Shows a pH-sensitive substrate specificity which may be ascribed to the protonation state of the binding site and leads to a stimulation of substrate transport in an acidic microenvironment. The exact transport mechanism has not been yet deciphered but most likely involves an anion exchange, coupling the cellular uptake of organic substrate with the efflux of an anionic compound. Hydrogencarbonate/HCO3(-) acts as a probable counteranion that exchanges for organic anions. Cytoplasmic glutamate may also act as counteranion in the placenta. An inwardly directed proton gradient has also been proposed as the driving force of E1S uptake with a (H(+):E1S) stoichiometry of (1:1) (By similarity).
Sequence Similarities
Belongs to the organo anion transporter (TC 2.A.60) family.
Tissue Specificity
Expressed in liver, kidney, small intestine mucosa, large intestine, brain, lung, spleen, stomach and heart.
Cellular localization
- Cell membrane
- Multi-pass membrane protein
- Basal cell membrane
- Multi-pass membrane protein
- Apical cell membrane
- Multi-pass membrane protein
Alternative names
Oatp2b1, Slc21a9, Slco2b1, Solute carrier organic anion transporter family member 2B1, Organic anion transporting polypeptide 2B1, Solute carrier family 21 member 9, OATP2B1