A Self-Consistent Molecular Mechanism of β₂-Microglobulin Aggregation.

Area of Science:

• Biochemistry
• Protein Misfolding Diseases
• Biophysics

Background:

• Dialysis-related amyloidosis (DRA) is linked to beta2-microglobulin (β2m) aggregation.
• The exact aggregation mechanism of β2m, especially concerning variants and pH, remains debated.
• Understanding β2m's behavior is crucial for managing DRA.

Purpose of the Study:

• To elucidate the aggregation mechanism of wild-type (WT) and pathogenic β2m variants (V27M, D76N).
• To investigate the influence of physiological and acidic pH on β2m aggregation.
• To characterize both the initiation (monomeric) and termination (fibrillar) states of β2m aggregation.

Main Methods:

• Utilized enhanced sampling approaches to characterize native monomeric and aggregated fibrillar states of β2m.
• Analyzed the behavior of WT and pathogenic β2m variants at neutral and acidic pH.
• Applied a propensity-stability approach to assess aggregation initiation and termination.

Main Results:

• Pathogenic β2m mutants retain more native folds at neutral pH compared to WT.
• At acidic pH, all variants show increased partially unfolded states, with varying extents (WT < V27M < D76N).
• All variants exhibit pH-dependent protofilament separation and increased binding affinity at acidic pH, with relative order WT < V27M < D76N.

Conclusions:

• β2m aggregation shifts from native-like to conformational switch-initiated fibrillation as pH decreases.
• Both aggregation initiation (propensity) and termination (stability) play critical roles in the overall process.
• The findings provide a mechanistic explanation for the heterogeneous behavior of β2m variants in DRA.