Sterolins are likely involved both in the selective transport of dietary cholesterol in and out of enterocytes and in selective sterol excretion by the liver into bile, as evidenced by the consequences when it is deficient or over expressed. The exact mechanism(s) whereby ABCG5/ABCG8 exert their effects on sterol metabolism has not yet been clarified. But it is suggested that the ABCG5/ABCG8 heterodimer shuttles cholesterol from the inner leaflet of the canalicular membrane through a chamber formed by the two half-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.