期刊
JOURNAL OF BIOLOGICAL CHEMISTRY
卷 276, 期 38, 页码 36020-36027出版社
AMER SOC BIOCHEMISTRY MOLECULAR BIOLOGY INC
DOI: 10.1074/jbc.M104665200
关键词
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Reabsorption of bile acids occurs in the terminal ileum by a Na+-dependent transport system composed of several subunits of the ileal bile acid transporter (IBAT) and the ileal lipid-binding protein. To identify the bile acid-binding site of the transporter protein IBAT, ileal brush border membrane vesicles from rabbit ileum were photoaffinity labeled with a radioactive 7-azi-derivative of cholyltaurine followed by enrichment of IBAT protein by preparative SDS gel electrophoresis. Enzymatic fragmentation with chymotrypisin yielded IBAT peptide fragments in the molecular range of 20.4-4 kDa. With epitope-specific antibodies generated against the C terminus a peptide of molecular mass of 6.6-7 kDa was identified as the smallest peptide fragment carrying both the C terminus and the covalently attached radio-labeled bile acid derivative. This clearly indicates that the ileal Na+/bile acid cotransporting protein IBAT contains a bile acid-binding site within the C-terminal 56-67 amino acids. Based on the seven-transmembrane domain model for IBAT, the bile acid-binding site is localized to a region containing the seventh transmembrane domain and the cytoplasmic C terminus. Alternatively, assuming the nine-transmembrane domain model, this bile acid-binding site is localized to the ninth transmembrane domain and the C terminus.
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