Interactions between the Conserved Hydrophobic Region of the Prion Protein and Dodecylphosphocholine Micelles

Abstract

The three-dimensional structure of PrP110 -136, a peptide encompassing the conserved hydrophobic region of the human prion protein, has been determined at high resolution in dodecylphosphocholine micelles by NMR. The results support the conclusion that the Ctm PrP, a transmembrane form of the prion protein, adopts a different conformation than the reported structures of the normal prion protein determined in solution. Paramagnetic relaxation enhancement studies with gadolinium-diethylenetriaminepentaacetic acid indicated that the conserved hydrophobic region peptide is not inserted symmetrically in the micelle, thus suggesting the presence of a guanidium-phosphate ion pair involving the side chain of the terminal arginine and the detergent headgroup. Titration of dodecylphosphocholine into a solution of PrP110 -136 revealed the presence of a surface-bound species. In addition, paramagnetic probes located the surface-bound peptide somewhere below the micelle-water interface when using the inserted helix as a positional reference. This localization of the unknown population would allow a similar ion pair interaction.

Dodecylphosphocholine Micelles Induce Amyloid Formation of the PrP(110-136) Peptide via an α-Helical Metastable Conformation

“…The initial intent of this study was to characterize the conformation of huPrP(110–136) interacting at the surface of DPC micelles (red signals in Fig 1) observed in our previous report[11]. The spread of resonances for this surface species indicated that the conformation was structured.…”

“…To illustrate the NMR data, a model of the surface-bound peptide was generated manually using Chimera[25] by using the Δδ 13 Cα data and the predicted backbone torsion angles (Φ,Ψ) (Fig 4). The peptide was also manually positioned on the micelle based on the PRE data from our previous study[11] using the α–helical micelle-inserted peptide model as a depth gauge.…”

“…If the peptide is allowed to fully insert in the micelle, it becomes trapped into a very stable α-helical conformation. In fact, NMR samples made for structural studies of this species were stable for more than a year[11]. In high peptide-to-micelle ratio situation, the peptide readily populates the inside of the micelle with the inserted α-helical conformation, while the excess stays at the headgroup-hydrophobic-core interface.…”

“…The preparation of 13 C, 15 N huPrP(110–136) NMR sample in DPC micelles and the details of NMR data collection, processing and analysis have been described elsewhere[11]. For this study a total of 28 liters of doubly labelled ( 13 C, 15 N) and 25 liters of 15 N-labelled of bacterial cultures were needed to obtain about 20 mg of purified 13 C, 15 N-huPrP(110–136) and about 12 mg of 15 N-huPrP(110–136).…”

“…Interactions between the prion protein, the above mutants, and membrane mimetics, such as bicelles[9], and dodecylphosphocholine (DPC) micelles[10], have been shown to produce amyloid fibrils. A detailed structural study of huPrP(110–136) showed the high propensity of this domain to adopt a curved α-helical conformation that is asymmetrically inserted in the detergent micelles[11]. This study suggested that the relative position of the helix within the micelle resulted from a salt bridge between the positively charged guanidine group of the terminal arginine (R136) and the negatively charged phosphate moiety of the detergent headgroup.…”