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UBC Theses and Dissertations

The human melanoma-associated antigen p97 is attached to the plasma membrane by a glycosyl-phosphatidylinositol anchor Food, Michael Robert


Melanotransferrin, or p97 is a cell surface glycoprotein which was first described as a marker antigen for human melanoma cells. Although p97 has a high level of amino acid sequence homology to human serum transferrin and lactoferrin its function has not yet been determined. One feature that distinguishes p97 from the other members of the transferrin family is the presence of a stretch of 24 hydrophobic amino acids at the C-terminus. In all previous studies, this sequence was thought to form a proteinacious transmembrane domain. In this study, however, sensitivity to bacterial phosphatidylinositol-specific phospholipase C, biosynthetic labelling with [³H]-ethanolamine, and partitioning in Triton X-114, were used to establish that p97 is expressed at the cell surface as a glycosyl-phosphatidylinositol anchored protein. As well, this anchor was shown to be present in p97 on human tumor lines and it apparently confers no special intracellular transport properties on the molecule. These findings raise important questions about the function of p97 and the possible involvement of this protein in a cellular iron uptake system that is independent from the transferrin/ transferrin receptor system.

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