Structure and dynamics of oligomeric intermediates in β2-microglobulin self-assembly

Area of Science:

• Biochemistry
• Protein Misfolding Diseases
• Structural Biology

Background:

• Beta(2)-microglobulin (β(2)M) is a protein known to form amyloid-like fibrils in vitro.
• Fibril morphology is highly dependent on solution conditions.
• Understanding the intermediate species in fibril formation is crucial for elucidating disease mechanisms.

Purpose of the Study:

• To characterize the oligomeric species during the formation of worm-like β(2)M fibrils at pH 3.6.
• To investigate the role of ionic strength in initiating and stabilizing these oligomers.
• To compare the oligomeric intermediates with those found in other fibril formation pathways.

Main Methods:

• Ion mobility spectrometry-mass spectrometry (IMS-MS) was employed to analyze oligomeric species.
• Samples were prepared at pH 3.6 with varying ionic strengths.
• Collision cross-sectional areas were calculated to infer oligomer structure.

Main Results:

• Upon dissolution, β(2)M exists as rapidly interconverting monomers and small oligomers (dimer to hexamer).
• Increasing ionic strength triggers fibril formation, stabilizing oligomers and forming higher-order species (7-mer to >14-mer).
• Oligomers exhibit linearly stacked structures with native-like subunit volumes.

Conclusions:

• The study identifies transient, oligomeric intermediates specific to worm-like β(2)M fibril assembly.
• These intermediates differ significantly from those observed in the formation of straight fibrils.
• The findings highlight the interrelationship between different fibril formation pathways and their divergence points.