Disease-related PrP(Sc) [pathogenic PrP (
prion protein)] is classically distinguished from its normal cellular precursor, PrP(C)(cellular PrP) by its
detergent insolubility and partial resistance to proteolysis. Although molecular diagnosis of
prion disease has historically relied upon detection of
protease-resistant fragments of PrP(Sc) using PK (
proteinase K), it is now apparent that a substantial fraction of disease-related PrP is destroyed by this
protease. Recently,
thermolysin has been identified as a complementary tool to PK, permitting isolation of PrP(Sc) in its full-length form. In the present study, we show that
thermolysin can degrade PrP(C) while preserving both PK-sensitive and PK-resistant
isoforms of disease-related PrP in both rodent and human
prion strains. For mouse RML (Rocky Mountain Laboratory)
prions, the majority of PK-sensitive disease-related PrP
isoforms do not appear to contribute significantly to infectivity. In vCJD (
variant Creutzfeldt-Jakob disease), the human counterpart of
BSE (bovine spongiform encephalopathy), up to 90% of total PrP present in the brain resists degradation with
thermolysin, whereas only approximately 15% of this material resists digestion by PK. Detection of PK-sensitive
isoforms of disease-related PrP using
thermolysin should be useful for improving diagnostic sensitivity in human
prion diseases.