Fibrillation of N-Terminal Prion Protein Fragment in Presence of Zinc Ions

Abstract

Abnormal (misfolded) form of human prion protein displays high propensity towards self-association which may result in formation of insoluble fibrillar deposits in the brain, associated with the development of fatal neurodegenerative disorders, transmissible spongiform encephalopathies (TSE) [1]. The formation of such deposits can be driven by many intra- and extracellular factors. One of them can be disrupted homeostasis of metal ions. As reported previously, Zn ions bonded to N-terminal fragment regulate the interactions between N- and C-terminals [2]. Here we present structural analysis of the fragment of PrP N-terminal domain in the presence of Zn ions. Our experiments demonstrate that Zn-saturation leads to formation of N-terminal domain fibrillar structures. The fibrils were analyzed by atomic force microscopy (AFM), electron microscopy (EM), X-ray fiber diffraction and X-ray absorption spectroscopy (XAS). AFM and EM images indicated, that in the presence of zinc, PrP peptide forms long fibrillar structures. The presence of two characteristic reflections at 1.12 nm and 0.36 nm in the X-ray diffraction pattern confirmed the fibrillar nature of the studied PrP peptide. These reflections corresponded to characteristic distances in the fibrillar structure of the studied PrP peptide. Zn XAS K-edge 1s->4p transition in the edge region indicates, that Zn occupies a mononuclear site and is coordinated by light atoms (N, O). Fourier transform of χ(k) signal indicates the presence of imidazole groups in the nearest Zn shell. Our findings may shed new light on the role of zinc in TSE disorders. This work was supported by the funds from the National Science Centre (Poland) granted on the basis of decision no. 2014/15/B/ST4/04839.[1] Kovacs, G. G., & Budka, H. (2008). The American Journal of Pathology, 172(3), 555-565. [2] Spevacek, A.R., et al. (2013) Structure, 21, 236-246.