Saturday, 15 July 2006

Are Soil Organic Colloids Effective in Entrapping Prion Proteins?.

Maria A. Rao, Fabio Russo, and Liliana Gianfreda. Dept of Soil, Plant and Environment Sciences, Univ of Naples Federico II, via Università 100, Portici, 80055, Italy

The dissemination of Transmissible Spongiform Encephalopathy (TSE) diseases is of great environmental concern because of their high risk for human and enviromental health. According to the “only-prion” hypothesis, prion is the infectious agent causative of TSE diseases and prion protein PrPc is a normal host cellular protein, refolded into a pathological form (PrPsc) following contamination by prions. In TSE infected tissues it is found in abnormal forms, which is proteinase K resistant and sedimentable. Soil is a natural sink of several contaminants potentially including also prion proteins. Accidental dispersion of prion proteins in soil occur from meat and bone meal storage plants, use of fertilizers augmented with meat and bone meal, decomposition of TSE contaminated animal carcasses buried in soil, TSE infected tissues, liquid and solid waste fragments from abattoirs, and wastes from TSE-infected animals. Therefore, understanding the retention and/or the dissemination of prion proteins in soils may be important for dealing with the dissemination of TSE infectivity. In soil prion proteins may become adsorbed and/or entrapped onto/in organic and organo-mineral colloids and preserve their activity and functionality. Severe variations of their structure may also occur which in the case of prion proteins might result in an increase of infectivity. The main goal of this paper was to investigate the interactions of a recombinant ovine prion protein (recPrP), used as a surrogate of PrPc, with synthetic organic matrices simulating natural organic soil colloids. A humic-like precursor, catechol, and an abiotic soil catalyst, birnessite interacted with recPrP giving rise to polymeric aggregates. The recPrP is a small protein (M.M 25 kD) with an isoelectric point of 9.0. Its structure is characterized by a well-folded C-terminal domain and a long, rather flexible N-terminal part, loading several positive amino acid residues. At pH < 9.0, the whole protein presents a net positive charge. HPLC, CHNS, FTIR, and CD investigations and extraction/desorption studies with strong and mild agents allowed to conclude that:(i)catechol was fully removed from the solution by the birnessite action; (ii) the protein was completely entrapped in the catechol polymers and its allocation within the polymers or on their surfaces depended on the relative sequence of catechol, birnessite and protein addition; (iii) any conformational change of recPrP structure occurred under all the investigated experimental conditions; (iv) comparative studies performed with a truncated recPrP form, i.e. with a protein missing the N part, indicated that the positive N part of recPrP had a main role in the interaction with the catechol polymers; (v)a quite irreversible sorption or entrapping of the protein in/on the polymers occurred at least with the extractive/desorptive conditions tested. All the above results seem to suggest that the investigated recPrP could be not easy mobile and possible not bioavailable in soil. Acknowledgment: This work was carried out with the support of Quality of Life Program (Contract QLK4-CT-2002-02493).

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