Thermodynamic Characterization of the Unfolding of the Prion Protein
National Centre for Biological Sciences, Tata Institute of Fundamental Research, Bangalore, IndiaBiophysical Journal (Impact Factor: 3.97). 01/2014; 106(2):410-20. DOI: 10.1016/j.bpj.2013.11.4491
The prion protein appears to be unusually susceptible to conformational change, and unlike nearly all other proteins, it can easily be made to convert to alternative misfolded conformations. To understand the basis of this structural plasticity, a detailed thermodynamic characterization of two variants of the mouse prion protein (moPrP), the full-length moPrP (23-231) and the structured C-terminal domain, moPrP (121-231), has been carried out. All thermodynamic parameters governing unfolding, including the changes in enthalpy, entropy, free energy, and heat capacity, were found to be identical for the two protein variants. The N-terminal domain remains unstructured and does not interact with the C-terminal domain in the full-length protein at pH 4. Moreover, the enthalpy and entropy of unfolding of moPrP (121-231) are similar in magnitude to values reported for other proteins of similar size. However, the protein has an unusually high native-state heat capacity, and consequently, the change in heat capacity upon unfolding is much lower than that expected for a protein of similar size. It appears, therefore, that the native state of the prion protein undergoes substantial fluctuations in enthalpy and hence, in structure.
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ABSTRACT: The susceptibility of the cellular prion protein (PrP(C)) to convert to an alternative misfolded conformation (PrP(Sc)), which is the key event in the pathogenesis of prion diseases, is indicative of a conformationally flexible native (N) state. In the present study, hydrogen-deuterium exchange (HDX) in conjunction with mass spectrometry and nuclear magnetic resonance spectroscopy have been used for the structural and energetic characterization of the N state of the full length mouse prion protein, moPrP (23-231) under conditions that favor misfolding. The kinetics of HDX of 34 backbone amide hydrogens in the N state were determined at pH 4. In contrast to the results of previous HDX studies on the human and Syrian hamster prion proteins at a higher pH, various segments of moPrP were found to undergo different extents of sub-global unfolding events at pH 4, a pH at which the protein is known to be primed to misfold to a β-rich conformation. No residual structure around the disulphide bond was observed for the unfolded state at pH 4. The N state of the prion protein is observed to be at equilibrium with at least two partially unfolded forms (PUFs). These PUFs, which are accessed by stochastic fluctuations of the N state, have altered surface area exposure relative to the N state. One of these PUFs resembles a conformation previously implicated to be an initial intermediate in the conversion of monomeric protein into misfolded oligomer at pH 4. Copyright © 2015, The American Society for Biochemistry and Molecular Biology.Journal of Biological Chemistry 08/2015; DOI:10.1074/jbc.M115.677575 · 4.57 Impact Factor
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