ABCG5 and ABCG8 form an obligate heterodimer that mediates Mg(2+)- and ATP-dependent sterol transport across the cell membrane (PubMed:16352607, PubMed:16867993, PubMed:18402465). Plays an essential role in the selective transport of the dietary cholesterol in and out of the enterocytes and in the selective sterol excretion by the liver into bile (PubMed:12444248, PubMed:14504269, PubMed:14657202, PubMed:25378657). Plays an important role in preventing the accumulation of dietary plant sterols in the body (PubMed:12444248, PubMed:14657202). Required for normal sterol homeostasis (PubMed:12444248, PubMed:14657202). The heterodimer with ABCG5 has ATPase activity (PubMed:16352607, PubMed:16867993). ATP + cholesterol(in) + H2O = ADP + cholesterol(out) + H(+) + phosphate ATP + H2O + sitosterol(in) = ADP + H(+) + phosphate + sitosterol(out) Cholesterol transport is inhibited by vanadate and by beryllium fluoride. Heterodimer with ABCG5. Detected in liver and jejunum (at protein level) (PubMed:12444248, PubMed:18402465, PubMed:25378657). Expressed in jejunum and ileum and, at lower level, in the liver (PubMed:11907139, PubMed:11099417, PubMed:12444248, PubMed:15040800, PubMed:25378657). Up-regulated in liver and small intestine by cholesterol feeding (PubMed:11099417). Possibly mediated by the liver X receptor/retinoic X receptor (LXR/RXR) pathway. Endotoxin (LPS) significantly decreased mRNA levels in the liver but not in the small intestine (PubMed:12777468). A functional Walker motif (consensus sequence G-X-X-G-X-G-K-[ST]-T) is expected to bind ATP. The essential Lys in this region is not conserved in ABCG8 (G-S-S-G-C-R-A-S) and is not required for transport activity mediated by the heterodimer with ABCG5. N-glycosylated (PubMed:12208867, PubMed:12444248, PubMed:16867993, PubMed:15054092, PubMed:18402465). N-glycosylation is important for efficient export out of the endoplasmic reticulum (PubMed:15054092). Mice are born at the expected Mendelian rate. They display decreased cholesterol levels, but strongly increased levels of the food-derived plant sterols campesterol and beta-sitosterol in blood plasma, liver and spleen (PubMed:25378657). Besides, mutant mice may have slightly increased total plasma triglyceride levels. Expression of Abcg5 is not affected. Mutant mice display decreased biliary sterol secretion (PubMed:15040800). Mice deficient for both Abcg5 and Abcg8 appear healthy and are fertile, but display strongly increased levels of the food-derived plant sterols sitosterol and campesterol in liver and blood plasma (PubMed:12444248, PubMed:14657202, PubMed:25378657). When mice are fed chow containing 0.02% cholesterol, cholesterol levels in blood plasma and in liver are considerably lower than in wild-type (PubMed:12444248, PubMed:14657202). In spite of the increased plasma and liver levels of plant sterols, and the decreased cholesterol levels, the total sterol levels in plasma and liver are closely similar in wild-type and mutant mice (PubMed:14657202). When mice are fed chow containing 2% cholesterol, plasma cholesterol levels remain stable in wild-type, but increase 2.4-fold in mutant mice. In the liver of mice kept on chow containing 2% cholesterol, cholesterol levels increase 3-fold for wild-type mice and 18-fold for mutant mice, resulting in much higher cholesterol levels than in wild-type livers (PubMed:12444248). Dietary cholesterol absorption appears normal in mutant mice, but the absorption of dietary cholestanol, campesterol and sitosterol is increased (PubMed:12444248). At the same time, mutant mice have very low cholesterol levels in bile, suggesting that the increased hepatic cholesterol levels are due to impaired cholesterol secretion into bile (PubMed:12444248). Likewise, the levels of the food-derived plant sterols stigmasterol, sitosterol, campesterol and brassicasterol are strongly decreased in bile from mutant mice (PubMed:14657202). In contrast, biliary phospholipid and bile acid levels appear unchanged relative to wild-type (PubMed:12444248). The blood plasma of mice with liver-specific or intestine-specific disruption of Abcg5 and Abcg8 has nearly normal levels of cholesterol, and mildly increased levels of sitosterol and campesterol (PubMed:25378657). Mice with intestine-specific disruption of Abcg5 and Abcg8 have strongly increased levels of sitosterol and campesterol in enterocytes, similar to that observed for mice with complete gene disruption (PubMed:25378657). In addition, they display strongly increased levels of sitosterol and campesterol in bile (PubMed:25378657). Mice with liver-specific disruption of Abcg5 and Abcg8 have slightly increased levels of campesterol and sitosterol in the liver, and normal, low levels of sitosterol and campesterol in bile (PubMed:25378657). Enterocytes and liver from mice with liver-specific or intestine-specific disruption of Abcg5 and Abcg8 have normal cholesterol levels (PubMed:25378657). Belongs to the ABC transporter superfamily. ABCG family. Eye pigment precursor importer (TC 3.A.1.204) subfamily. Seems to have a defective ATP-binding region.