Fibril formation of the rabbit/human/bovine prion proteins.

Prion diseases are infectious fatal neurodegenerative diseases including Creutzfeldt-Jakob disease in humans and bovine spongiform encephalopathy in cattle. The misfolding and conversion of cellular PrP in such mammals into pathogenic PrP is believed to be the key procedure. Rabbits are among the few mammalian species that exhibit resistance to prion diseases, but little is known about the molecular mechanism underlying such resistance. Here, we report that the crowding agents Ficoll 70 and dextran 70 have different effects on fibrillization of the recombinant full-length PrPs from different species: although these agents dramatically promote fibril formation of the proteins from human and cow, they significantly inhibit fibrillization of the rabbit protein by stabilizing its native state. We also find that fibrils formed by the rabbit protein contain less ß-sheet structure and more α-helix structure than those formed by the proteins from human and cow. In addition, amyloid fibrils formed by the rabbit protein do not generate a proteinase K-resistant fragment of 15-16-kDa, but those formed by the proteins from human and cow generate such proteinase K-resistant fragments. Together, these results suggest that the strong inhibition of fibrillization of the rabbit PrP by the crowded physiological environment and the absence of such a protease-resistant fragment for the rabbit protein could be two of the reasons why rabbits are resistant to prion diseases.

[Concentration and Size Distribution Characteristics of Culturable Bioaerosols at Various Air Quality Levels During Fall and Winter in Xi'an, China].

The concentration and size distribution of culturable bacteria and fungi were studied in Xi'an city at various air quality levels. The culturable bioaerosols were collected by an Andersen bioaerosol aerosol sampler between Sept. 2014 and Jan. 2015. Principal component analysis and multiple linear regressions were applied to link the concentrations with meteorological conditions including ambient temperature and relative humidity, as well as the levels of air pollutants such as PM2.5, PM10, NO2, SO2, and O3. These measured results showed that the concentration of culturable bacteria and fungi were in the ranges of 97-1909 CFU·m-3 and 92-1737 CFU·m-3, respectively. The concentrations of culturable bioaerosols increased along with a deterioration in air quality. The size distribution of the bacteria migrated to coarse particles. Fungal aerosols showed a normal distribution at low pollution levels, while for a high levels, they preferenced fine particles. Results from the principal component analysis (PCA) indicate that the concentration of culturable bioaerosols is mainly influenced by haze, solar radiation, and relative humidity. Multiple linear regression analysis showed that bacterial aerosol concentrations are positively correlated with haze (P<0.05) and relative humidity, while no significant negative correlations with solar radiation exists. Fungal aerosol concentrations did not have significant positive correlations with haze, solar radiation, or relative humidity. The results of this study will provide basic data for evaluating the effects of bioaerosols on human health and the environment.