A yeast ATP-binding cassette-type protein mediating ATP-dependent bile acid transport

Abstract

ATP-dependent transport of bile acids is a key determinant of bile flow in mammalian liver and is associated with cholesterol excretion, gallstone formation, and numerous inherited and acquired hepatobiliary diseases. Secretory vesicles and a vacuole enriched fraction purified from Saccharomyces cerevisiae also exhibit ATP-dependent bile acid transport. ATP-dependent transport of bile acids by the vacuolar fraction was independent of the vacuolar proton ATPase, responded to changes in the osmotically sensitive intravesicular space, and was saturable, exhibiting a Km of 63 microM for taurocholate. The BAT1 (bile acid transporter) gene was isolated from yeast DNA by polymerase chain reaction amplification using degenerate oligonucleotides hybridizing to conserved regions of ABC-type proteins. ATP-dependent bile acid transport was abolished when the BAT1 coding region was deleted from the genome and restored upon reintroduction of the gene. The deduced amino acid sequence predicts that Bat1p is an ABC-type protein 1661 amino acids in length, similar to mammalian cMOAT/cMRP1 and MRP1 transporters, yeast Ycf1p, and two yeast proteins of unknown function. Information obtained from the yeast BAT1 gene may aid identification of the gene encoding the mammalian bile acid transporter.