Thermodynamic characterization for the denatured state of bovine prion protein and the BSE associated variant E211K

Authors: Hwang, Soyoun; Nicholson, Eric

Submitted to: Prion
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/3/2018
Publication Date: 10/24/2018
Citation: Hwang, S., Nicholson, E.M. 2018. Thermodynamic characterization for the denatured state of bovine prion protein and the BSE associated variant E211K. Prion. 12(5-6):301-309. https://doi.org/10.1080/19336896.2018.1534485.
DOI: https://doi.org/10.1080/19336896.2018.1534485

Interpretive Summary: A genetic change in the coding sequence of the prion gene in cattle results in a glutamic acid to lysine substitution at position 211 in the prion protein (PrP). This amino acid substitution is termed E211K and has been associated with a genetic form of bovine spongiform encephalopathy (BSE). Here, we have compared the protein secondary structure using a spectroscopic technique known as circular dichroism (CD) and completed detailed thermodynamic analysis of the folding of recombinant wild type and E211K variants of the bovine prion protein monitoring the unfolding of the protein based on the loss of protein structure due to increased temperature or addition of chemical denaturant using CD. The secondary structure of the E211K variant was essentially identical to that of the wild type indicating that the native states of the protein are the same. The protein thermodynamic stability of E211K substitution showed a slight destabilization relative to the wild type consistent with results reported for recombinant human prion protein and its mutant E200K. However, the wild type bovine PrP exhibits a more compact denatured state relative to the E211K variant as evidenced by lower change in heat capacity of unfolding and m-value for the wild-type relative to E211K. This denatured state difference has implications for existing models of PrPC to PrPSc conversion suggesting that the wild-type PrP starts the folding process from a more highly structured state that may be protective with regard to alternative folding pathways that result in the disease conformation than the disease associated variant E211K.

Technical Abstract: Propagation of transmissible spongiform encephalopathies is believed to involve the conversion of cellular prion protein, PrPC, into a misfolded oligomeric form, PrPSc. The most common hereditary prion disease is a genetic form of Creutzfeldt-Jakob disease (CJD) in humans, in which a mutation in the prion gene results in a glutamic acid to lysine substitution at position 200 in the prion protein. Similarly, this amino acid substitution at residue 211 in cattle, homologous mutation to E200K in humans, has been associated with a case of bovine spongiform encephalopathy. Here, we have compared the protein secondary structure using circular dichroism and completed detailed thermodynamic analysis of the folding of recombinant wild type and E211K variants of the bovine prion protein. The secondary structure of the E211K variant was essentially identical to that of the wild type. The protein thermodynamic stability of E211K substitution showed a slight destabilization relative to the wild type consistent with results reported for recombinant human prion protein and its mutant E200K. However, the wild type bovine PrP exhibits a more compact denatured state relative to the E211K variant as evidenced by a reduced change in heat capacity of unfolding, (deltadeltaCp = 0.24 kcal/mol/K). This denatured state difference has implications for existing models of PrPc to PrPSc conversion via an intermediate and suggests that enhanced disease associated with the naturally occurring variant may result from differences in the denatured state conformation.