The Same Primary Structure of the Prion Protein Yields Two Distinct Self-propagating States

Abstract

The question of whether distinct self-propagating structures could be formed within the same amino acid sequence in the absence of external cofactors or templates has important implications for a number of issues, including the origin of prion strains and the engineering of smart, self-assembling peptidebased biomaterials. In the current study, we showed that chemically identical prion protein can give rise to conformationally distinct, self-propagating amyloid structures in the absence of cellular cofactors, post-translational modification, or PrP Scspecified templates. Even more surprising, two self-replicating states were produced under identical solvent conditions, but under different shaking modes. Individual prion conformations were inherited by daughter fibrils in seeding experiments conducted under alternative shaking modes, illustrating the high fidelity of fibrillation reactions. Our study showed that the ability to acquire conformationally different self-propagating structures is an intrinsic ability of protein fibrillation and strongly supports the hypothesis that conformational variation in selfpropagating protein states underlies prion strain diversity.The existence of multiple prion strains is considered to be one of the most puzzling features of prion biology. According to the protein-only hypothesis of prion propagation, the normal cellular isoform of the prion protein, PrP C , can be converted into a range of self-propagating disease-related structures, referred to as strains of PrP Sc (1). Although certain physical properties are common for all PrP Sc strains, each strain also possesses unique strain-specific conformational features. Within the protein-only hypothesis, it is assumed that variation in PrP Sc structure can give rise to a broad range of strain-specific disease phenotypes, including substantial variation in incubation time to disease, in pathology, and in behavioral symptoms.In the past several years considerable evidence has accumulated indicating that prion strains do, indeed, exhibit notable differences in the amount and type of ␤-sheet structure, conformational stability, proteolytic resistance, and surface-exposed epitopes (2-7). Although the results of these aforementioned studies were consistent with the protein-only hypothesis, the primary origin of strain-specific conformational variations remains unclear. What is the possible source of strain-specific structural variation in PrP Sc ? A "unified theory" of prion propagation postulates that the strain-specific features of the prion infectious agent may be encoded by a coprion, or small nucleic acid (8). Alternatively, the ability to adopt multiple self-propagating structures may be an intrinsic property of the fibrillation reaction itself and can be achieved in the absence of a coprion. In the past, two distinct amyloid states were produced from chemically identical A␤ peptides (9); however, this property has never been demonstrated for fibrillation of larger polypeptides or global proteins such as PrP.In the current study...

Globular Domain of the Prion Protein Needs to Be Unlocked by Domain Swapping to Support Prion Protein Conversion

“…Recently several prion strains were produced in vitro, differing primarily in fibril morphology (67,68) and also in incubation periods in inoculated mice (68). By epitope accessibility studies using a panel of antibodies we showed that the fibrils of mutants with engineered disulfides are indistinguishable from WT fibrils.…”

Partially Unfolded Forms of the Prion Protein Populated under Misfolding-promoting Conditions

“…This region shows a dependence of exchange rates on denaturant concentration identical to that of the C-terminal end of ␣1, which is unusual for residues in loop regions. It has been reported in the case of human PrP that the C-terminal residues 153-156 of ␣1 undergo a pH-induced elongation to form a 3 10 helix at neutral pH (60) that becomes disordered at lower pH. In moPrP, residues Met 153 -Tyr 156 were observed to be protected at pH 4, resulting in slow HDX of these residues.…”

Distinct Stability States of Disease-Associated Human Prion Protein Identified by Conformation-Dependent Immunoassay

“…Polymorphisms in the host prion protein gene in part determine susceptibility to infection and modify the resultant disease phenotype, but in order to explain the existence of distinct strains, PrP Sc has been proposed to exist in different, stable, and replicative biophysical forms or "conformers" that "encipher" strain-like properties (reviewed in references 1 and 11). Recent reports of the successful production of prion infectivity with distinct structural and biological properties, from recombinant PrP, strongly support the prion hypothesis in general and the structural variant hypothesis in particular (9,(23)(24)(25)(26)(27)(28)51).…”