Structure of interacting segments in the growing amyloid fibril of beta2-microglobulin probed with IR spectroscopy

Area of Science:

• Biochemistry
• Structural Biology
• Biophysics

Background:

• Beta2-microglobulin (beta2m) is a protein prone to amyloid fibril formation, implicated in diseases like dialysis-related amyloidosis.
• Understanding the structural dynamics of amyloid fibril growth is crucial for developing therapeutic strategies.

Purpose of the Study:

• To investigate the inter-segmental interactions at the growing tip of beta2m amyloid fibrils.
• To elucidate the structural contribution of the fibril tip to overall fibril formation.

Main Methods:

• Infrared (IR) microscopy was employed to analyze amyloid fibril structure.
• Cross-seeding techniques were used, generating beta2m fragment fibrils on pre-formed beta2m fibrils.

Main Results:

• The structure of the fibril tip was characterized using IR spectroscopy.
• Fewer residues (6.5 +/- 1.0) in the cross-seeded fibril tip adopted a beta-sheet conformation compared to spontaneous fibrils (7.5 +/- 1.1) at pH 2.5.
• The tip exhibited a planar structure, suggesting planarity of the interacting segment.

Conclusions:

• The fibril tip structure influences beta-sheet content and peptide orientation.
• N- and C-terminal regions of the beta2m fragment show differential solvent exposure and protonation, dictating peptide directionality within the fibril.