Prions, the infectious agents of various prion diseases such as bovine spongiform encephalopathy (BSE), are composed primarily of a misfolded protein designated PrPSc. PrPSc retains its infectivity after undergoing routine sterilizing processes under high pressure or by treatment with disinfectants. To establish a safe and effective method for inactivating PrPSc, we investigated bacterial proteolytic enzymes and determined their digestive activities against PrPSc by Western blotting technique. When PrPSc-infected mouse brain homogenates were incubated with a culture supernatant of a Bacillus strain MSK103 containing the enzyme for 1 hour at 37ºC, no visible PrPSc band was observed in Western blotting analysis, indicating that the MSK-103 enzyme had a highly proteolytic activity against PrPSc. The proteolytic activity of the enzyme was higher than that of a keratinase, PWD-1. In addition, the purified enzyme was distinct from the keratinase in several biochemical characteristics such as molecular weight, isoelectric point and optimal pH. These findings suggest that the MSK-103 enzyme is a novel proteolytic enzyme and may be useful to disinfect PrPSc-contaminated tools and instruments. (Safety Technology Research Team, Prion Disease Research Center TEL +81-29-838-7840)
