BIOPHYSICAL AND FUNCTIONAL STUDY OF THE PrPc:STI-1 COMPLEX
Romano, S.A.1; Cordeiro, Y.2,3; Lima, L.M.T.R.3; Torriani, I.4; Silva, J.L.2; Foguel, D.2 and Linden, R.1
1IBCCF, UFRJ, Brazil; 2IBqM, UFRJ, Brazil; 3Faculdade de Farmácia, UFRJ, Brazil; 4Laboratório Nacional de Luz Síncrotron, Brazil.
Prion diseases or spongiform encephalopathies are related to the cellular prion protein (PrPc), abundantly expressed in the central nervous system. During the course of the disease, PrPc is transformed in a pathological isoform, PrPSc, leading to neurodegeneration through accumulation of this abnormally folded protein. Numerous studies have focused on the pathological properties of PrPc, however, its cellular function is still unclear. Lately, it was shown that PrPc participates in a cell surface multi-protein complex, which is involved in cell-cell and cell-extracellular matrix interactions modulating neuronal survival and differentiation [1]. One of the PrPc-binding proteins is the stress-inducible protein (STI-1), which induces trophic and neuroprotective signals through the recruitment of neuronal PrPc. The present work aims to investigate the biophysical and biochemical properties of the PrPc:STI-1 interaction. Binding of PrPc to STI-1 was investigated by fluorescence anisotropy and circular dichroism (CD) measurements. Small-angle X-ray scattering (SAXS) allowed us to obtain information on the molecular envelope of the PrPc:STI-1 complex. Confirming previous in vivo data, the in vitro formation of the PrPc:STI-1 complex was evidenced by a gradual increment of the fluorescence anisotropy values of fluorescein-labeled PrPc as the STI-1 concentration was increased. The CD results showed appreciable modifications in the secondary structure of both proteins upon complex formation. From the SAXS data we could calculate the molecular radii of monomeric STI-1 and of the complex. The obtained values were significantly higher then those belonging to monomeric proteins, indicating that complex formation induced an overall change in the protein structures. Interestingly, this work evidenced that the PrPc:STI-1 interaction led to significant modifications in their secondary structures, suggesting a potential role of these structural modifications in the signalling properties of the complex.
[1] Lopes, M. H.; Hajj, G. N. M.; Muras, A. G.; Mancini, G. L.; Castro, R. M. P. S.; Ribeiro, K. C. B.; Brentani, R. R.; Linden, R. and Martins, V. R. (2005) Journal of Neuroscience 25, 11330-11339.
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