A structural model for Alzheimer's beta -amyloid fibrils based on experimental constraints from solid state NMR

Area of Science:

• Biophysics
• Neuroscience
• Structural Biology

Background:

• Alzheimer's disease is linked to amyloid fibril formation.
• Amyloid fibrils are characterized by a cross-beta structural motif.
• The structure of Abeta(1-40) fibrils remains incompletely understood.

Purpose of the Study:

• To present a detailed structural model of amyloid fibrils formed by Abeta(1-40).
• To integrate experimental data from solid-state NMR, X-ray fiber diffraction, and electron microscopy.
• To elucidate the molecular organization within Abeta(1-40) fibrils.

Main Methods:

• Solid-state Nuclear Magnetic Resonance (NMR) spectroscopy to derive experimental constraints.
• X-ray fiber diffraction to confirm the cross-beta structural motif.
• Electron microscopy to determine fibril dimensions and mass-per-length.

Main Results:

• A structural model for Abeta(1-40) fibrils was developed.
• The N-terminal 10 residues of Abeta(1-40) are structurally disordered.
• Residues 12-24 and 30-40 form parallel beta-sheets, creating a double-layered beta-sheet structure with a hydrophobic core.
• Residues 25-29 form a backbone bend, facilitating sidechain interactions within the core.
• Charged residues D23 and K28 form salt bridges within the hydrophobic core.
• Minimum diameter fibrils comprise two cross-beta units with juxtaposed hydrophobic faces.

Conclusions:

• The proposed structural model provides insights into Abeta(1-40) fibril assembly.
• The model highlights the role of hydrophobic interactions and specific salt bridges in stabilizing the fibril structure.
• Understanding this structure is crucial for developing therapeutic strategies against Alzheimer's disease.