Structural insights into Aβ42 oligomers using site-directed spin labeling

Area of Science:

• Biochemistry
• Structural Biology
• Neuroscience

Background:

• Oligomerization of amyloid-beta 42 (Aβ42) is central to Alzheimer disease pathogenesis.
• The precise structures of toxic Aβ42 oligomers remain poorly understood.
• Site-directed spin labeling (SDSL) is a potent technique for studying disordered systems.

Purpose of the Study:

• To comprehensively characterize the structure of toxic Aβ42 oligomers, termed globulomers.
• To explore the utility of SDSL in amyloid oligomer structural studies.
• To elucidate the structural arrangement within Aβ42 globulomers.

Main Methods:

• Site-directed spin labeling (SDSL) coupled with electron paramagnetic resonance (EPR) spectroscopy.
• Transmission electron microscopy (TEM) for morphology.
• Circular dichroism (CD) for secondary structure.
• X-ray powder diffraction (XRPD) for packing.
• Mobility and distance measurements at 14 residue positions.

Main Results:

• Aβ42 globulomers are globular structures (∼7-8 nm diameter) with predominantly β-structures.
• SDSL revealed both structured and disordered states across all labeled positions.
• Structural order increases from the N- to C-terminus.
• Intermolecular distances (11.5-12.5 Å) indicate a tightly packed C-terminal core (residues 29-40).

Conclusions:

• The observed distances rule out parallel in-register beta-sheet structures typical of fibrils.
• Results strongly suggest an antiparallel β-sheet arrangement within Aβ42 globulomers.
• SDSL is effective for characterizing the complex structures of amyloid oligomers.