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

Abstract

Glycosaminoglycans (GAGs), particularly heparin, are known to reduce the toxicities of various amyloidogenic proteins. The molecular factors underlying the antitoxic effects of GAGs, however, are still not fully understood. Because interactions of amyloidogenic proteins and their aggregates with membranes are believed to play major roles in affecting amyloid pathogenesis, our objective in this study was to elucidate the effect of heparin on membrane interactions of the 21-residue amyloidogenic determinant of the prion protein [PrP(106-126)]. Indeed, the experimental results indicate that heparin significantly interferes in membrane interactions of the prion peptide. Specifically, we show that there is direct competition for binding of PrP(106-126) between heparin on the one hand and negatively charged phospholipids on the other hand. The data reveal that heparin, even in very low molar concentrations, exhibited high affinity towards PrP(106-126) and consequently suppressed interactions of the peptide with lipid vesicles. Interestingly, whereas heparin significantly inhibited lipid-induced PrP(106-126) fibrillation, it still promoted fibril formation in aqueous solutions independently of the lipid vesicles present. Our results strongly suggest that the primary effects of GAGs in attenuating amyloid toxicities are due to blocking of membrane interactions of the amyloidogenic proteins rather than modulation of their fibrillation properties.

Lipid Bilayers Significantly Modulate Cross-Fibrillation of Two Distinct Amyloidogenic Peptides

“…Membrane-induced fibrillation of amyloid peptides, including IAPP and PrP, have been previously reported. 22,23 The ThT data in Figure 1, however, point to a dramatic fibrillation enhancement when PrP(106−126) and IAPP were mixed and then added to the DMPC/DMPG suspension. Indeed, the fluorescence emission ThT when added to the PrP(106−126) and IAPP together in the presence of the lipid vesicles (Figure 1, vi) was substantially higher in comparison with either the two peptides without lipids (Figure 1, v), but also as compared to the individual peptides incubated separately with the lipid vesicles (Figure 1, iv, ii).…”

“…Essentially, this peptide had a negligible effect upon the FRET between the vesicle-embedded donors and acceptors except for the last time point, in which the prion fragment increased FRET efficiency, indicating a different bilayer binding mechanism as compared to IAPP. 22 The IAPP/PrP(106−126) mixture, however, gave rise to a significantly different FRET time evolution as compared to the two peptides added separately (Figure 2, long dash). Initially, the peptide mixture induced lesser FRET upon addition to the NBD-PE/Rh-PE/DMPC/DMPG vesicles, similar to IAPP alone.…”

“…27 Specifically, lipid reorganization and bilayer fluidity changes induced by amphiphilic or hydrophobic substances have been shown to modulate the FRET between membrane-embedded dyes. 22,28,29 In the context of this work, FRET experiments have been previously applied for evaluating bilayer interactions of amyloidogenic peptides. 22,30 The FRET time evolutions recorded in NBD-PE/Rh-PE/ DMPC/DMPG vesicles (1:1:500:500 molar ratio) depicted in Figure 2 indicate that the IAPP/PrP(106−126) mixture exerted a distinct impact upon lipid bilayers as compared to the effects of the individual peptides incubated separately with the vesicles.…”

“…22,28,29 In the context of this work, FRET experiments have been previously applied for evaluating bilayer interactions of amyloidogenic peptides. 22,30 The FRET time evolutions recorded in NBD-PE/Rh-PE/ DMPC/DMPG vesicles (1:1:500:500 molar ratio) depicted in Figure 2 indicate that the IAPP/PrP(106−126) mixture exerted a distinct impact upon lipid bilayers as compared to the effects of the individual peptides incubated separately with the vesicles. Specifically, incubation of IAPP alone with the NBD-PE/Rh-PE/DMPC/DMPG vesicles gave rise to lower energy transfer as compared to the control vesicles.…”

Conformational conversion of prion protein in prion diseases

“…Highly basic unstructured N-terminal domain of prion protein is the common interaction site of GAGs, nucleic acids and lipids. Heparin was found to significantly interfere in membrane interactions of the PrP106-126 and inhibit lipid-induced fibrillation [159]. Similarly, low molecular weight heparin can form soluble complex with PrP in a pH-dependent way, and this binding can prevent RNA-induced aggregation [160].…”