Polymerization of murine recombinant prion protein in nucleic acid solution

Recombinant prion protein has been used earlier to understand the structura l properties of cellular prion protein PrPC and to understand conformationa l change of PrPC to its isoform, PrPSc which is believed to be responsible for the prion disease. Here we report that murine recombinant prion protein , MoPrPC polymerizes in the presence of nucleic acid. The aggregation proce ss and the properties of the aggregates have been monitored by physical, bi ochemical and ultrastructural studies. An increase in the turbidity at 0,90 degrees light scattering is observed when the protein is added to nucleic acid. An increase in the fluorescence of anilino naphthalene sulfonic acid dye (ANS) accompanying a blue shift in its emission maxima is observed when the aggregate obtained from prion protein and DNA reaction is added to it. The kinetics of the increase of the ANS fluorescence during aggregation pr ocess show lag periods which depend linearly on the nucleic acid concentrat ion but show a biphasic dependence on the protein concentration. The change in the fluorescence properties of the dye in the presence of the aggregate s obtained in the present study and in the presence of the protein PrP 27-3 0 amyloid isolated in vivo reported in literature are similar. The dye Cong o Red binds to the aggregates resulting from the aggregation reaction. The ultrastructural analysis revealed polymeric structures with amyloid like mo rphologies and smaller oligomeric structures. In addition, condensed nuclei c acid structures are also observed which are morphologically different fro m histone induced condensed nucleic acid structures but are similar to Huma n Immunodeficiency Virus-1 nucleocapsid protein, NCp7, induced nucleic acid structures. The aggregates show resistance to degradation by proteinase K treatment. Charge neutralization resulting from the MoPrPC-DNA interaction and accompanying structural changes in the molecules may explain the observ ed effects.