Prion proteins (PrP) are proteins implicated in transmissible spongiform encephalopathies (TSE). Their fate in soil is a matter of concern for both animal and human health. Assessment of dissemination risk requires an understanding of the mechanisms of interaction between prions and soil solid surfaces. Ovine PrPrec (alpha or beta structured) was used as a model of the prion entity. Montmorillonite, mica and amorphous silica were chosen as models of soil surfaces. The structure of the adsorbed protein was examined by FTIR spectroscopy [1]. The organisation of the protein layer was determined by NMR spectroscopy. The PrPrec adsorbed amount was quantified by NMR, FTIR, radiolabeling (125-I) and depletion approaches (Western blot, ELISA). Desorption was explored in stationary or laminar flow conditions [2]. An important observation was the correlation between the PrPrec structural changes and the irreversibility of adsorption. Two types of interaction were identified: (i) With montmorillonite, alpha to beta conversion occurred. Very stringent conditions (extreme pH, detergents, high ionic strength) did not achieve desorption and competition with other proteins (animal serum) did not alter the level of PrPrec adsorption, either on montmorillonite or mica. Comparison between full length and N-truncated protein behaviour, suggested combined hydrophobic and electrostatic effects associated with the N-terminal part. (ii) On amorphous silica, no structural conversion occurred and the adsorption was completely reversible. An electroelution process was devised allowing efficient removal of PrPrec from montmorillonite and applicable to crude soil samples [3]. It might open the way to quantitative and sensitive detection of prions in soil. Considering the high efficiency of PrPrec retention by montmorillonite (2g protein/g montmorillonite at pH 7), trapping of infectivity is currently under investigation. As a whole, this study leads to novel information on PrPrec structure in contact with surfaces, opens practical tracks for decontamination and gives indication on possible mode of dissemination of prions in soils and waters.

[1] Revault M., Quiquampoix H., Baron M.H. and Noinville S. (2005). Fate of prions in soil : Trapped conformation of full-length ovine prion protein induced by adsorption on clays. Biochimica et Biophysica Acta – General Subjects, 1724, 367-374. [2] Vasina E.N., Dejardin P., Rezaei H., Grosclaude J. and Quiquampoix H. (2005). Fate of prions in soil : Adsorption kinetics of recombinant unglycosylated ovine prion protein onto mica in laminar flow and subsequent desorption. Biomacromolecules, 6, 3425-3432. [3] Rigou P., Rezaei H., Grosclaude J. and Quiquampoix H. Fate of prions in soil : Entrapment capacity of model clay for prion protein enlightens remanence mechanisms in natural soils. Submitted.

This work is part of the European Contract QLK4-CT-2002-02493 : Biotic and Abiotic Mechanisms of TSE Infectivity Retention and Dissemination in Soil (TSE-SOIL-FATE).