ABCG5 and ABCG8 form an obligate heterodimer that mediates Mg(2+)- and ATP-dependent sterol transport across the cell membrane. Plays an essential role in the selective transport of dietary plant sterols and cholesterol in and out of the enterocytes and in the selective sterol excretion by the liver into bile. Required for normal sterol homeostasis. The heterodimer with ABCG8 has ATPase activity. ATP + cholesterol(in) + H2O = ADP + cholesterol(out) + H(+) + phosphate ATP + H2O + sitosterol(in) = ADP + H(+) + phosphate + sitosterol(out) Heterodimer with ABCG8. Detected in liver (at protein level). Expressed only in liver and intestine. The Walker motif (consensus sequence G-X-X-G-X-G-K-[ST]-T) is expected to bind ATP. Within this motif, the conserved Lys is essential for transport activity mediated by the heterodimer with ABCG8. N-glycosylated. N-glycosylation is important for efficient export out of the endoplasmic reticulum. The polymorphism at position 583 is found in strains SHR, SHRSP and Wistar Kyoto which are both hypertensive and sitosterolemic. Strains which are hypertensive but not sitosterolemic do not contain a polymorphism at this position. Belongs to the ABC transporter superfamily. ABCG family. Eye pigment precursor importer (TC 3.A.1.204) subfamily.