Clustered Negative Charges on the Lipid Membrane Surface Induce β-Sheet Formation of Prion Protein Fragment 106−126

Abstract

The conformational conversion of prion protein (PrP) from an alpha-helix-rich normal cellular isoform (PrPC) to a beta-sheet-rich pathogenic isoform (PrPSc) is a key event in the development of prion diseases, and it takes place in caveolae, cavelike invaginations of the plasma membrane. A peptide homologous to residues 106-126 of human PrP (PrP106-126) is known to share several properties with PrPSc, e.g., the capability to form a beta-sheet and toxicity against PrPC-expressing cells. PrP106-126 is thus expected to represent a segment of PrP that is involved in the formation of PrPSc. We have examined the effect of lipid membranes containing negatively charged ganglioside, an important component of caveolae, on the secondary structure of PrP106-126 by circular dichroism. The peptide forms an alpha-helical or a beta-sheet structure on the ganglioside-containing membranes. The beta-sheet content increases with an increase of the peptide:lipid ratio, indicating that the beta-sheet formation is linked with self-association of the positively charged peptide on the negatively charged membrane surface. Analogous beta-sheet formation is also induced by membranes composed of negatively charged and neutral glycerophospholipids with high and low melting temperatures, respectively, in which lateral phase separation and clustering of negatively charged lipids occur as shown by Raman spectroscopy. Since ganglioside-containing membranes also exhibit lateral phase separation, clustered negative charges are concluded to be responsible for the beta-sheet formation of PrP106-126. In caveolae, clustered ganglioside molecules are likely to interact with the residue 106-126 region of PrPC to promote the PrPC-to-PrPSc conversion.

Heparin Inhibits Membrane Interactions and Lipid‐Induced Fibrillation of a Prion Amyloidogenic Determinant

“…PrP(106-126) has been widely studied as a surrogate of the full-length prion [25] because its neurotoxic activity and fibrillation properties are similar to those of the full-length prion protein. [18,[26][27][28] Although previous studies have focused on the effects of lipids and membranes upon PrP(106-126) [29,30] or the reciprocal impact of the prion peptide on lipid bilayers, [31][32][33][34][35] no comprehensive, unified analysis has examined the relationship between heparin and membrane interactions of PrP(106-126).…”

Membrane-mediated amyloid formation of PrP 106–126: A kinetic study

“…It is more suitable for the SUV kinetic experiments. As shown by Miura et al[41], the membrane binding affinity of PrP peptides is enhanced by lowering pH to ~6. We performed all of our experiments at pH = 6.…”

“…Indeed, membranes have been implicated as the catalyst that facilities amyloid formation (see review [17, 48, 49]). For many peptides, such as Aβ [17, 50] IAPP[18, 29, 51], PrP [41], and penetratin[45, 52] it has been known that unstructured peptide monomers in solution transform into α-helices upon binding to membranes. As the bound peptide to lipid ratio, P b / L , increases, peptides were found in β-sheets, presumably in an aggregated form.…”

“…On the other hand, it was also found to increase the membrane conductance without any evidence of discrete channel or pore formation or ion selectivity[16]. Miura et al[41] studied the circular dichroism (CD) spectra of PrP 106-126 as a function of peptide-to-lipid ratio and the role of negatively charged lipids, particularly that of gangliosides in its β-sheet formation. Their results are invaluable for our design of kinetic experiments.…”

Is PrP(106-126) Fragment Involved in the Membrane Activity of the Prion Protein?

“…Finally, GM1, a ganglioside abundantly expressed in neurons with anionic nature and concentrated in lipid rafts regions [70,71], has been suggested to promote oligomerization and accelerate amyloid fibril formation by the Alzheimer A peptide [70,72,73]. In addition, the clustering of the negatively-charged GM1 in raft domains has also been suggested to promote the binding of the full length PrP C through 106-126 region and to promote the conversion of PrP C into PrP Sc [74]. The possible role of GM1 in the membrane affinity of PrP(106-126) and it implication in vesicle disruption was explored with vesicles composed of POPC/GM1(9:1).…”