Essential component of the Ost-alpha/Ost-beta complex, a heterodimer that acts as the intestinal basolateral transporter responsible for bile acid export from enterocytes into portal blood (PubMed:15563450, PubMed:16317684, PubMed:17650074, PubMed:18292224, PubMed:22535958). Efficiently transports the major species of bile acids (taurocholate) (PubMed:16317684, PubMed:17650074, PubMed:18292224, PubMed:22535958). Taurine conjugates are transported more efficiently across the basolateral membrane than glycine-conjugated bile acids (PubMed:16317684). Can also transport steroids such as estrone 3-sulfate and dehydroepiandrosterone 3-sulfate, therefore playing a role in the enterohepatic circulation of sterols (By similarity). Able to transport eicosanoids such as prostaglandin E2 (By similarity). taurocholate(out) = taurocholate(in) tauroursodeoxycholate(out) = tauroursodeoxycholate(in) glycoursodeoxycholate(out) = glycoursodeoxycholate(in) glycocholate(out) = glycocholate(in) taurochenodeoxycholate(out) = taurochenodeoxycholate(in) glycochenodeoxycholate(out) = glycochenodeoxycholate(in) taurodeoxycholate(out) = taurodeoxycholate(in) glycodeoxycholate(out) = glycodeoxycholate(in) prostaglandin E2(out) = prostaglandin E2(in) estrone 3-sulfate(out) = estrone 3-sulfate(in) dehydroepiandrosterone 3-sulfate(out) = dehydroepiandrosterone 3-sulfate(in) Interacts with SLC51B. The Ost-alpha/Ost-beta complex is a heterodimer composed of alpha (SLC51A) and beta (SLC51B) subunit. Mainly restricted to the lateral and basal membranes of ileal enterocytes. Transported from the endoplasmic reticulum to the plasma membrane upon interacting with SLC51B. Present at high levels in ileum. In ileum, it is restricted to the apical domain on the mature villus enterocytes with little detectable expression in the goblet cells or crypt enterocytes (at protein level). Expressed in kidney but not in heart, brain, liver, spleen, embryo, lung, thymus, ovary nor testis. Positively regulated via the bile acid-activated nuclear receptor farnesoid X receptor (NR1H4/FXR). Up-regulated in mice lacking Mrp4, but it is unable to compensate for the absence of Mrp4. N-glycosylated. Mice are physically indistinguishable from wild-type mice but display strongly reduced transileal transport of taurocholate. Moreover, the bile acid pool size is significantly reduced, but fecal bile acid excretion is not elevated. Belongs to the OST-alpha family.