Abstract
The presence of the prion protein (PrP) in normal human urine is controversial and currently inconclusive. This issue has taken a special relevance because prion infectivity has been demonstrated in urine of animals carrying experimental or naturally occurring prion diseases, but the actual presence and tissue origin of the infectious prion have not been determined. We used immunoprecipitation, one- and two-dimensional electrophoresis, and mass spectrometry to prove definitely the presence of PrP in human urine and its post-translational modifications. We show that urinary PrP (uPrP) is truncated mainly at residue 112 but also at other residues up to 122. This truncation makes uPrP undetectable with some commonly used antibodies to PrP. uPrP is glycosylated and carries an anchor which, at variance with that of cellular PrP, lacks the inositol-associated phospholipid moiety, indicating that uPrP is probably shed from the cell surface. The detailed characterization of uPrP reported here definitely proves the presence of PrP in human urine and will help determine the origin of prion infectivity in urine.
Highlights
The normal or cellular prion protein (PrPC)4 is predominantly a cell surface protein that is sensitive to proteases and is soluble in non-ionic detergents [1,2,3,4]
The structure of the GPI anchor, which is thought to be identical for the full-length and the C1 fragment, is made of a glycan core attached to the PrPC C terminus through a phosphodiester linkage of phosphoethanolamine, and a hydrophobic phospholipid component made of phosphatidylinositol and fatty acid that mediates the attachment to the membrane [12, 13]
Immunoblotting with the anti-N Ab failed to detect the PrP-immunoreactive protein in urine
Summary
The presence of the prion protein (PrP) in normal human urine is controversial and currently inconclusive. The detailed characterization of uPrP reported here definitely proves the presence of PrP in human urine and will help determine the origin of prion infectivity in urine. The GPI anchor links both full-length PrPC and the C1 fragment to the external surface of the plasma membrane of the cell. Shaked et al [26] originally reported the detection of PrPSc by Western blotting with the monoclonal antibody 3F4 in the urine of prion-affected Syrian hamsters and human subjects.
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