Organic Solute Transporter Alpha (OSTa)

OST-alpha together with OST-beta is able to transport estrone sulfate, taurocholate, digoxin, and prostaglandin E2 across cell membranes. The Ost-alpha / Ost-beta heterodimer, but not the individual subunits, stimulates sodium-independent bile acid uptake. OST-alpha and OST-alpha have high expression in the testis, colon, liver, small intestine, kidney, ovary, and adrenal gland. The deduced mouse and human OST-alpha proteins contain 340 amino acids and share 89% amino acid identity. Both proteins have 7 transmembrane domains, a predicted hydrophilic cytosolic loop between transmembrane domains 3 and 4, and a conserved stretch of cysteines. Organic solute transporter alpha-beta (Ostalpha-Ostbeta) is a heteromeric bile acid and sterol transporter that facilitates the enterohepatic and renal-hepatic circulation of bile acids.