Structural Heterogeneity in the Preamyloid Oligomers of β-2-Microglobulin

Area of Science:

• Biochemistry
• Structural Biology
• Biophysics

Background:

• Dialysis-related amyloidosis is caused by beta-2 microglobulin (β2m) amyloid fibril formation in dialysis patients.
• Understanding the initial stages of β2m amyloid assembly is critical for developing therapeutic strategies.

Purpose of the Study:

• To investigate the early, soluble preamyloid oligomers of β2m using native electrospray ionization and ion mobility mass spectrometry.
• To elucidate the structural characteristics and conformational heterogeneity of β2m oligomers during copper(II)-induced amyloid formation.

Main Methods:

• Native electrospray ionization (ESI) coupled with ion mobility mass spectrometry (IM-MS) to analyze soluble β2m oligomers.
• Experimental data combined with molecular modeling and molecular dynamics simulations to determine oligomer structures.
• Selective depletion of copper(II)-bound species to study Cu(II)-free tetrameric conformers.

Main Results:

• ESI-IM-MS identified multiple conformers for β2m dimers, tetramers, and hexamers preceding amyloid formation.
• The predominant dimer is a Cu(II)-bound structure with an antiparallel side-by-side configuration.
• Tetramers exist in both Cu(II)-bound and Cu(II)-free forms, with the latter exhibiting compact and expanded conformers, suggesting a role for conformational heterogeneity in Cu(II)-induced amyloidogenesis.

Conclusions:

• Conformational heterogeneity in β2m tetramers is essential for copper(II)-induced amyloid formation, differing from other amyloid systems.
• The identified Cu(II)-free tetramer models provide insights into copper(II) release mechanisms.
• This study lays the groundwork for developing novel inhibition strategies against dialysis-related amyloidosis.