Sterolin-1 and –2 are two ‘half’ adenosine triphosphate binding (ATP) cassette (ABC) transporters which found to be indispensable for the regulation of sterol absorption and excretion.
In 1998, sitosterolemia (STSL) locus has been mapped to the short arm of human chromosome 2 (2p21) after studying 10 well-characterized families with this disorder.
In 2001, The STSL locus was found to be comprises two genes, ABCG5 and ABCG8, encoding 2 members of the ABC-transporter family, named sterolin-1 and sterolin-2, respectively, Sterolin-2, discovered after sterolin-1, is located <400 base pair (bp) upstream of sterolin-1 in the opposite orientation.
However, the ABCG or White subfamily with its five fully characterized human members consists of half-size ABC proteins which probably dimerize to form active membrane transporters.
Following ATP binding and hydrolysis, the complex undergoes a conformational change, flipping a cholesterol molecule into the outer membrane leaflet in a configuration that favors its release into the canalicular space.