Title : Structural study on the glycosyl-phosphatidylinositol anchor and
the asparagine-linked sugar chain asparagine-linked sugar chain of a soluble
form of CD59 in human urine
Abstract :
- CD59 is an 18-kDa glycoprotein widely expressed on human cells
- An important structural feature of CD59 is its attachment to the cell surface via a glycosyl-phosphatidylinositol ( GPI ) anchor
- CD59 , like many GPI-anchored proteins , has been found in urine, serum, and other body fluids
- The structures of the GPI anchor and the asparagine-linked sugar chain asparagine-linked sugar chain of a soluble form of CD59 in urine, U- CD59 , were determined
- Purified U- CD59 released 1 mol of inositol per mole of protein by nitrous acid deamination, which cleaved between glucosamine and inositol present commonly in the GPI anchor
- This indicates that a GPI anchor, which ended with inositol, is linked at the carboxy terminus of U- CD59
- The peptide containing an asparagine-linked sugar chain and the peptide containing a glycan portion asparagine-linked sugar chain and the peptide containing a glycan portion of the GPI anchor were isolated after trypsin digestion of U- CD59
- The asparagine-linked sugar chains and the glycan portion asparagine-linked sugar chains and the glycan portion of the GPI anchor were isolated from these peptides following hydrazinolysis or deamination and dephosphorylation, respectively
- Their structures were analyzed by sequential exoglycosidase digestion and methylation analyses
- The structures of the asparagine-linked sugar chains asparagine-linked sugar chains of U- CD59 were biantennary complex type , only 4.2% of which are monosialylated
- The backbone structure of the GPI anchor was similar to that of Try-panosoma brucei variant surface glycoprotein , but showed significant variations in its side- chain moieties
- This is the first detailed structural analysis of the human GPI anchor and the first detailed analysis of the carboxyl-terminal structure of the soluble-form GPI-anchored protein
- The results indicate that the backbone structure of the GPI anchor is conserved from parasites to human and that at least a part of the soluble-form GPI-anchored protein has the structure produced by the action of glycan-phosphatidylinositol-specific phospholipase D