Structural details of amyloid β oligomers in complex with human prion protein as revealed by solid-state MAS NMR spectroscopy

Anna S König,Nadine S Rösener,Lothar Gremer,Markus Tusche,Daniel Flender,Elke Reinartz,Wolfgang Hoyer,Philipp Neudecker,Dieter Willbold,Henrike Heise

doi:10.1016/j.jbc.2021.100499

Abstract

Human PrP (huPrP) is a high-affinity receptor for oligomeric amyloid β (Aβ) protein aggregates. Binding of Aβ oligomers to membrane-anchored huPrP has been suggested to trigger neurotoxic cell signaling in Alzheimer’s disease, while an N-terminal soluble fragment of huPrP can sequester Aβ oligomers and reduce their toxicity. Synthetic oligomeric Aβ species are known to be heterogeneous, dynamic, and transient, rendering their structural investigation particularly challenging. Here, using huPrP to preserve Aβ oligomers by coprecipitating them into large heteroassemblies, we investigated the conformations of Aβ(1–42) oligomers and huPrP in the complex by solid-state MAS NMR spectroscopy. The disordered N-terminal region of huPrP becomes immobilized in the complex and therefore visible in dipolar spectra without adopting chemical shifts characteristic of a regular secondary structure. Most of the well-defined C-terminal part of huPrP is part of the rigid complex, and solid-state NMR spectra suggest a loss in regular secondary structure in the two C-terminal α-helices. For Aβ(1–42) oligomers in complex with huPrP, secondary chemical shifts reveal substantial β-strand content. Importantly, not all Aβ(1–42) molecules within the complex have identical conformations. Comparison with the chemical shifts of synthetic Aβ fibrils suggests that the Aβ oligomer preparation represents a heterogeneous mixture of β-strand-rich assemblies, of which some have the potential to evolve and elongate into different fibril polymorphs, reflecting a general propensity of Aβ to adopt variable β-strand-rich conformers. Taken together, our results reveal structural changes in huPrP upon binding to Aβ oligomers that suggest a role of the C terminus of huPrP in cell signaling. Trapping Aβ(1–42) oligomers by binding to huPrP has proved to be a useful tool for studying the structure of these highly heterogeneous β-strand-rich assemblies.

Highlights

The solution structure of Human PrP (huPrP)(23–230) had originally been determined in acetate buffer at an acidic pH of 4.5 and a temperature of 20 C (48), whereas the huPrP-amyloid β (Aβ)(1–42)oligo complex samples for solid-state NMR were prepared at a pH value close to neutral
Quantitative analysis reveals that the Random Coil Index (RCI) order parameters (50) SRCI2, which are a measure of how different the backbone chemical shifts are from those of a disordered random coil on a scale of 0 to 1, are consistently below ≈0.6 (Fig. S3)
In this study we investigated the interaction of Aβ(1–42)oligo and huPrP by solid-state NMR spectroscopy

Summary

Introduction

A comparison between a solid-state NMR 13C-13C correlation spectrum of Aβoligo in complex with huPrP(23–144) and a 13C-13C TOCSY correlation spectrum of Aβ monomers in solution (Fig. 5) reveals strong chemical shift differences and indicates that the Aβ monomer building blocks in oligomers have undergone significant structural changes upon oligomerization.

Results

Conclusion