Transmissible spongiform encephalopathies are fatal neurodegenerative disorders thought to be transmitted by self-perpetuating conformational conversion of a neuronal membrane glycoprotein (PrPC, for "cellular prion protein") into an abnormal state (PrPSc, for "scrapie prion protein"). Doppel (Dpl) is a protein that shares significant biochemical and structural homology with PrPC. In contrast to its homologue PrPC, Dpl is unable to participate in prion disease progression or to achieve an abnormal PrPSc-like state. We have constructed a chimeric mouse protein, composed of the N-terminal domain of PrPC (residues 23-125) and the C-terminal part of Dpl (residues 58-157). This chimeric protein displays PrP-like biochemical and structural features; when incubated in presence of NaCl, the alpha-helical monomer forms soluble beta-sheet-rich oligomers which acquire partial resistance to pepsin proteolysis in vitro, as do PrP oligomers. Moreover, the presence of aggregates akin to protofibrils is observed in soluble oligomeric species by electron microscopy. (c) 2007 Elsevier Inc. All rights reserved.