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 cerevisiaealso 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 K m of 63 μmfor taurocholate. The BAT1 (bileacid 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 theBAT1 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.
Footnotes
-
↵* This work was supported in part by National Institutes of Health Grants DK51005–01 (to D. F. O.) and DK35652 (to I. M. A.), and by the Center for Gastroenterology Research on Absorptive and Secretory Processes under Public Health Service Grant 1 P30 DK39428.The costs of publication of this article were defrayed in part by the payment of page charges. The article must therefore be hereby marked “advertisement” in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.
-
↵‡ To whom correspondence should be addressed: Dept. of Physiology, Tufts University School of Medicine, 136 Harrison Ave., Boston, MA 02111.
-
↵1 The abbreviations used are: BA, bile acid; aa, amino acid(s); ABC, ATP-binding cassette; BAT, bile acid transporter; CMV, canalicular membrane vesicles; DNPSG, 2,4-dinitrophenyl glutathione; NBD, nucleotide binding domain; SG, synthetic growth medium; MES, 4-morpholineethanesulfonic acid, AMP-PNP, adenosine 5′-(β,γ-imino)triphosphate; PCR, polymerase chain reaction; nt, nucleotide(s); bp, base pair(s); kb, kilobase pair(s); PAGE, polyacrylamide gel electrophoresis; CAPS, 3-(cyclohexylamino)propanesulfonic acid.
-
↵2 D. F. Ortiz, L. F. Epstein, J. A. Wemmie, S. Moye-Rowley, and I. M. Arias, submitted for publication.
-
- Received March 6, 1997.
