RNA Binding Activity of the N-terminal Domain of Prion Protein
Gomes, M. P. B.1; Cordeiro, Y1,2; Lima, L. M. T. R. 2, Foguel, D1. & Silva, J. L.1
1IBqM, UFRJ; 2 Faculdade de Farmácia, UFRJ.
Transmissible Spongiform Encephalopathies (TSEs) are a group of fatal neurodegenerative diseases characterized by lost of motor control, paralysis and dementia. The most commons TSEs are Bovine Spongiform Encephalopathy in cattle, Scrapie in sheep and Creutzfeldt-Jakob Disease in humans. It is generally accepted that an infectious isoform of the cellular prion protein (PrPC) is the major responsible for occurrence of TSEs. The PrPC is a constitutive protein among all mammals, attached to the membrane of neurons and cells of the lymphoreticular system by a GPI anchor. The onset of a TSE is related to a conformational change in PrPC, which loses most of its a-helical content, becoming a b-sheet rich protein, the PrPSc (Sc from Scrapie). The mechanisms that lead to this conformational change are still unclear. It is believed that an additional unknown factor may be involved, perhaps by influencing the PrPCÞPrPSc transition. Our previous findings show that nucleic acids induce PrPC to acquire some characteristics of PrPSc. Based on these results we propose an updated hypothesis, in which nucleic acids can act by serving as catalysts and/or chaperones in the conversion, and not by encoding genetic information. In this work we relate experimental data on the interactions of RNA with the murine recombinant PrP (rPrP 23-231), with specific focus on secondary and tertiary structure changes, with the aid of spectroscopic techniques. In agreement with prior findings we observed interaction between rPrP and RNA extracted from Neuroblastoma cultured cells (N2aRNA). RNA induces a drastic change in rPrP 23-231, leading to immediate increase in light scattering, indicative of aggregation, and lost of a-helical structure monitored by circular dichroism. After seven days of observation, no significant gain of b-sheet structure was detected. We investigate the role of the amino-terminal region in those interactions, using PrP constructs lacking portions of this region (rPrP D32-121 and rPrP D51-90). Interestingly, unlike the rPrP 23-231, we verified no changes in the secondary structure content for both constructs in the presence of N2aRNA and no significant increase in light scattering. These data suggest that the N-terminal region may be directly involved in PrP-RNA interaction.
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