Inhibition of the Human Sodium/Bile Acid Cotransporters by Side-Specific Methanethiosulfonate Sulfhydryl Reagents:  Substrate-Controlled Accessibility of Site of Inactivation

Mammalian sodium/bile acid cotransporters (SBATs) constitute a subgroup of the sodium cotransporter superfamily and function in the enterohepatic circulation of bile acids. They are glycoproteins with an exoplasmic N-terminus, seven or nine transmembrane segments, and a cytoplasmic C-terminus. They...

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Bibliographic Details
Published in:Biochemistry (Easton) 2000-06, Vol.39 (22), p.6743-6750
Main Authors: Hallén, Stefan, Fryklund, Jan, Sachs, George
Format: Article
Language:English
Subjects:
Amino Acid Sequence
Animals
Bile Acids and Salts - metabolism
Bile Acids and Salts - pharmacology
Biological Transport - drug effects
Carrier Proteins - antagonists & inhibitors
Carrier Proteins - genetics
Cell Line
Enzyme Inhibitors - pharmacology
Humans
Kinetics
Mesylates - pharmacology
Molecular Sequence Data
Mutagenesis, Site-Directed
Organic Anion Transporters, Sodium-Dependent
Sulfhydryl Reagents - pharmacology
Symporters
Taurocholic Acid - metabolism
Transfection
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Summary:Mammalian sodium/bile acid cotransporters (SBATs) constitute a subgroup of the sodium cotransporter superfamily and function in the enterohepatic circulation of bile acids. They are glycoproteins with an exoplasmic N-terminus, seven or nine transmembrane segments, and a cytoplasmic C-terminus. They exhibit no significant homology with other members of the sodium cotransporter family and there is limited structure/function information available for the SBATs. Membrane-impermeant methanethiosulfonates (MTS) inhibited bile acid transport by alkylation of cysteine 270 (apical SBAT)/266 (basolateral SBAT) that is fully conserved among the sodium/bile acid cotransporters. The accessibility of this residue to MTS reagent is regulated by the natural substrates, sodium and bile acid. In experiments with the apical SBAT, sodium alone increases the reactivity with the thiol reagents as compared to sodium-free medium. In contrast, bile acids protect the SBATs from inactivation, although only in the presence of sodium. The inhibition and protection data suggest that cysteine 270/266 lies in a sodium-sensitive region of the SBATs that is implicated in bile acid transport.
ISSN:0006-2960
1520-4995
DOI:10.1021/bi000577t