Characterisation of the ATP-dependent taurocholate-carrier protein (gp110) of the hepatocyte canalicular membrane.
The canalicular domain-specific glycoprotein gp110, which recently has been shown to function as an ATP-dependent taurocholate transporter, has been purified 1800-fold from rat liver plasma membranes. gp110 has been characterised as an integral plasma membrane protein with M(r) of 100,000-115,000 and pI of 2.5-3.5 and possesses a highly glycosylated and negatively charged extra-cellular domain. The broad range of M(r) and pI values results from the existence of numerous glycoforms composed of sialylated N-glycans. After deglycosylation, the polypeptide has M(r) 48,000 and pI 5.0. In primary cultures of rat hepatocytes, gp110 is synthesised with M(r) 110,000, while in the presence of tunicamycin the non-glycosylated form has M(r) 48,000. In the presence of 1-deoxymannojirimycin, two forms of M(r) 83,000 and M(r) 91,000 were found, which were converted by endo-beta-N-acetylglucosaminidase H into a single 52,000-M(r) band, indicating the existence of two basic glycoforms at the oligomannosyl stage of biosynthesis. gp110 was phosphorylated at serine residues in primary cultures of hepatocytes. The sequences of ten internal peptides of gp110 were identical to the sequence of the high-M(r) form of ecto-ATPase, but ecto-ATPase activity from plasma-membrane extracts was not depleted by anti-(gp110) serum. In contrast, Fab fragments of these antibodies inhibit the aggregation of freshly isolated hepatocytes.
Institut für Molekularbiologie und Biochemie, Freie Universität Berlin, Germany.
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Becker
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Lucka
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Kilian
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Kannicht
W
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Reutter
D018528:ATP-Binding Cassette Transporters; D000255:Adenosine Triphosphate / Q000494:pharmacology*; D000595:Amino Acid Sequence; D000818:Animals; D001648:Bile Canaliculi / Q000737:chemistry* / Q000648:ultrastructure; D002352:Carrier Proteins / Q000737:chemistry / Q000302:isolation & purification* / Q000378:metabolism; D002448:Cell Adhesion; D002462:Cell Membrane / Q000737:chemistry; D002478:Cells, Cultured; D006031:Glycosylation; D007163:Immunosorbent Techniques; D007526:Isoelectric Point; D008099:Liver / Q000737:chemistry* / Q000648:ultrastructure; D017038:Mannosyl-Glycoprotein Endo-beta-N-Acetylglucosaminidase / Q000378:metabolism; D008969:Molecular Sequence Data; D008970:Molecular Weight; D010766:Phosphorylation; D051381:Rats; D017421:Sequence Analysis; D013656:Taurocholic Acid / Q000378:metabolism
D018528:ATP-Binding Cassette Transporters; D002352:Carrier Proteins; C038659:taurocholate carrier protein, rat; D013656:Taurocholic Acid; D000255:Adenosine Triphosphate; D017038:Mannosyl-Glycoprotein Endo-beta-N-Acetylglucosaminidase