Amyloid formation under physiological conditions proceeds via a native-like folding intermediate

Area of Science:

• Biochemistry
• Structural Biology
• Molecular Biology

Background:

• Protein misfolding and aggregation into amyloid fibrils are implicated in various diseases.
• The in vivo mechanisms of amyloid fibril formation remain largely unknown, particularly under physiological conditions.
• Identifying specific aggregation-prone species is crucial for understanding disease pathogenesis.

Purpose of the Study:

• To elucidate the in vivo pathway of amyloid fibril formation for the naturally amyloidogenic protein beta-2-microglobulin.
• To identify the specific protein species that directly precede fibril elongation under physiologically relevant conditions (pH 7.0, 37°C).
• To characterize the structural properties of these aggregation-prone intermediates.

Main Methods:

• Detailed analysis of the folding mechanism of beta-2-microglobulin at pH 7.0 and 37°C.
• Correlation of the concentrations of different folding species with the rate of fibril elongation.
• Structural characterization of identified intermediates using Nuclear Magnetic Resonance (NMR) spectroscopy.

Main Results:

• A specific folding intermediate, featuring a non-native trans-proline isomer, was identified as the direct precursor of fibril elongation.
• This intermediate exhibits a highly native-like structure but with perturbed edge strands.
• These perturbations likely expose normally protected regions, facilitating self-association.

Conclusions:

• Amyloid formation pathways can involve the self-assembly of highly native-like folding intermediates.
• Understanding these intermediates is key to developing strategies for preventing amyloid disorders.
• The findings provide a structural basis for the aggregation of beta-2-microglobulin and potentially other amyloidogenic proteins.