AGFD 201 |
| Prions are composed solely of an alternatively folded isoform of the prion protein (PrP), designated PrPSc. The polyoxometalate phosphotungstic acid (PTA) has been used to separate PrPSc from its precursor PrPC (the normal cellular isoform) by selective precipitation. In contrast to PrPC, PrPSc has not been solubilized using nondenaturing detergents Because of the similarities between PrPSc and lipoproteins with respect to hydrophobicity and formation of PTA complexes, we investigated whether these molecules bind to each other in blood. We found that prions from the brains of patients with sporadic Creutzfeldt-Jakob disease (sCJD) bind to very low-density and low-density lipoproteins (VLDL and LDL, respectively) but not to high-density lipoproteins (HDL) or other plasma components as demonstrated by both immunoassay and electron microscopy. Immunoassays demonstrated that apolipoprotein B (apoB), which is the major protein component of VLDL and LDL, also bound native PrPSc through a highly cooperative process. Exposure to 4 M guanidine (Gdn) HCl at 80°C for 20 min resulted in the release of approximately 50% of the PrPSc bound to LDL particles. The apparent binding constants of native human (Hu) PrPSc or denatured recombinant HuPrP(90–231) for apoB and LDL ranged from 28 to 212 pM. HuPrPSc was detected in VLDL and LDL fractions of plasma collected from sCJD patients but not in the HDL or immunoglobulin fractions. Whether detection of PrPSc in VLDL and LDL particles can be adapted into an antemortem diagnostic test for prions in the blood of humans and livestock remains to be determined. |
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Sterling Hendricks Memorial Lectureship
8:00 AM-12:00 PM, Wednesday, 13 September 2006 San Francisco Marriott -- Salon 8, Oral
Division of Agricultural & Food Chemistry |