1. Laboratory of Molecular and Cellular Neurobiology, IRCCS San Raffaele Pisana, Via di Val Cannuta, 247 00166 Rome, Italy
2. Laboratory of Prion Neurobiology, Department of Neuroscience, Istituto di Ricerche Farmacologiche Mario Negri, Via G. La Masa, 19 20156 Milan, Italy
3. Department of Chemical Engineering, Arizona State University, P.O. Box 876106, Tempe, AZ 85287-6106, USA