The human prion protein alpha2 helix: a thermodynamic study of its conformational preferences.
We have synthesized both free and terminally-blocked peptide corresponding to the second helical region of the globular domain of normal human prion protein, which has recently gained the attention of structural biologists because of a possible role in the nucleation process and fibrillization of prion protein. The profile of the circular dichroism spectrum of the free peptide was that typical of alpha-helix, but was converted to that of beta-structure in about 16 h. Instead, below 2.1 x 10(-5) M, the spectrum of the blocked peptide exhibited a single band centered at 200 nm, unequivocally associated to random conformations, which did not evolve even after 24 h. Conformational preferences of this last peptide have been investigated as a function of temperature, using trifluoroethanol or low-concentration sodium dodecyl sulfate as alpha- or beta-structure inducers, respectively. Extrapolation of free energy data to zero concentration of structuring agent highlighted that the peptide prefers alpha-helical to beta-type organization, in spite of results from prediction algorithms. However, the free energy difference between the two forms, as obtained by a thermodynamic cycle, is subtle (roughly 5-8 kJ mol(-1) at any temperature from 280 K to 350 K), suggesting conformational ambivalence. This result supports the view that, in the prion protein, the structural behavior of the peptide is governed by the cellular microenvironment.
Tizzano
Barbara
B
Dipartimento di Chimica Biologica, Università Federico II di Napoli, Napoli, Italy.
Palladino
Pasquale
P
De Capua
Antonia
A
Marasco
Daniela
D
Rossi
Filomena
F
Benedetti
Ettore
E
Pedone
Carlo
C
Ragone
Raffaele
R
Ruvo
Menotti
M
D006801:Humans; D011328:Prions / Q000737:chemistry* / Q000378:metabolism; D011487:Protein Conformation; D017433:Protein Structure, Secondary; D012967:Sodium Dodecyl Sulfate; D013816:Thermodynamics
D011328:Prions; D012967:Sodium Dodecyl Sulfate