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Molecular Mechanism of Taurocholate Transport by the Bile Salt Export Pump, an ABC Transporter Associated with Intrahepatic Cholestasis.

Abstract：

:The bile salt export pump (BSEP/ABCB11) transports bile salts from hepatocytes into bile canaliculi. Its malfunction is associated with severe liver disease. One reason for functional impairment of BSEP is systemic administration of drugs, which as a side effect inhibit the transporter. Therefore, drug candidates are routinely screened for potential interaction with this transporter. Hence, understanding the functional biology of BSEP is of key importance. In this study, we engineered the transporter to dissect interdomain communication paths. We introduced mutations in noncanonical and in conserved residues of either of the two nucleotide binding domains and determined the effect on BSEP basal and substrate-stimulated ATPase activity as well as on taurocholate transport. Replacement of the noncanonical methionine residue M584 (Walker B sequence of nucleotide binding site 1) by glutamate imparted hydrolysis competency to this site. Importantly, this mutation was able to sustain 15% of wild-type transport activity, when the catalytic glutamate of the canonical nucleotide binding site 2 was mutated to glutamine. Kinetic modeling of experimental results for the ensuing M584E/E1244Q mutant suggests that a transfer of hydrolytic capacity from the canonical to the noncanonical nucleotide binding site results in loss of active and adoption of facilitative characteristics. This facilitative transport is ATP-gated. To the best of our knowledge, this result is unprecedented in ATP-binding cassette proteins with one noncanonical nucleotide binding site. Our study promotes an understanding of the domain interplay in BSEP as a basis for exploration of drug interactions with this transporter.

journal_name

Mol Pharmacol

journal_title

Molecular pharmacology

authors

Sohail MI,Schmid D,Wlcek K,Spork M,Szakács G,Trauner M,Stockner T,Chiba P

doi

10.1124/mol.117.108688

subject

Has Abstract

pub_date

2017-10-01 00:00:00

pages

401-413

issue

4

eissn

0026-895X

issn

1521-0111

pii

mol.117.108688

journal_volume

92

pub_type

杂志文章

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