Identification of a Mutation in the Ileal Sodium-dependent Bile Acid Transporter Gene That Abolishes Transport Activity ()

• Published in: The Journal of biological chemistry 1995-11, Vol.270 (45), p.27228-27234
• Main Authors: Wong, Melissa H., Oelkers, Peter, Dawson, Paul A.
• Format: Article
• Language: English
• Subjects: Amino Acid Sequence; Animals; Base Sequence; Bile Acids and Salts - metabolism; Biological Transport, Active - drug effects; Carrier Proteins - chemistry; Carrier Proteins - genetics; Carrier Proteins - metabolism; Cell Line; Cell Membrane - metabolism; Cloning, Molecular; Cricetinae; Crohn Disease - genetics; Crohn Disease - metabolism; DNA Primers - genetics; DNA, Complementary - genetics; Female; Glycosylation; Humans; Ileum - metabolism; Male; Molecular Sequence Data; Organic Anion Transporters, Sodium-Dependent; Pedigree; Point Mutation; Polymorphism, Single-Stranded Conformational; Recombinant Fusion Proteins - chemistry; Recombinant Fusion Proteins - genetics; Recombinant Fusion Proteins - metabolism; Sodium - metabolism; Symporters; Taurocholic Acid - metabolism; Transfection
• ISSN: 0021-9258; 1083-351X
• DOI: 10.1074/jbc.270.45.27228

The ileal Na+/bile acid cotransporter plays a critical role in the reabsorption of bile acids from the small intestine. In the course of cloning and characterizing the human ileal Na+/bile acid cotransporter cDNA, a dysfunctional isoform was identified in a patient diagnosed with Crohn's disease. Expression studies using hamster-human ileal Na+/bile acid cotransporter cDNA chimeras narrowed the location of the defect to the carboxyl-terminal 94 amino acids. Comparison of the sequence of the dysfunctional isoform to that of a wild-type human ileal Na+/bile acid cotransporter genomic clone revealed a single C to T transition resulting in a proline to serine substitution at amino acid position 290. The inheritance of this mutation in the proband's family was confirmed by single-stranded conformation polymorphism analysis and DNA sequencing. In transfected COS-1 cells, the single amino acid change abolished taurocholate transport activity but did not alter the transporter's synthesis or subcellular distribution. This dysfunctional mutation represents the first known molecular defect in a human sodium-dependent bile acid transporter.