Mapping the structural transition in an amyloidogenic apolipoprotein A-I

Area of Science:

• Biochemistry
• Structural Biology
• Molecular Biology

Background:

• Human apolipoprotein A-I (apoA-I) is crucial for lipid metabolism.
• The Iowa mutation (G26R) in apoA-I is linked to amyloid fibril formation.
• Understanding the structural basis of apoA-I aggregation is vital for disease research.

Purpose of the Study:

• To investigate the molecular mechanisms by which the G26R mutation in apoA-I induces amyloid formation.
• To characterize the structural and functional changes associated with the apoA-IIOWA variant.

Main Methods:

• Electron paramagnetic resonance (EPR) spectroscopy to analyze protein structure.
• Electron microscopy to visualize protofibril formation.
• Lipid-binding assays and protease sensitivity experiments.

Main Results:

• The G26R mutation in apoA-I (apoA-IIOWA) decreases lipid-binding capability and increases protease sensitivity.
• The mutation promotes the formation of beta-secondary structures in regions 27-56.
• Electron microscopy revealed the formation of annular protofibrils, and amyloidophilic dyes indicated widespread aggregation in vitro.

Conclusions:

• The G26R mutation disrupts the native structure of apoA-I, promoting beta-strand formation and subsequent amyloid aggregation.
• Loss of Gly26's role in beta-strand termination and the introduction of Arg27 contribute to the proamyloidogenic nature of apoA-IIOWA.
• These structural alterations have significant functional consequences, including impaired lipid binding and aggregation into insoluble fibrils.