Fibrillar vs crystalline full-length beta-2-microglobulin studied by high-resolution solid-state NMR spectroscopy

Area of Science:

• Biochemistry
• Structural Biology
• Biophysics

Background:

• Amyloid fibrils are linked to protein misfolding and aggregation diseases.
• Dialysis-related amyloidosis is caused by beta-2-microglobulin (beta2m) forming amyloid fibrils.
• Understanding fibril structure and formation is crucial for disease insight.

Purpose of the Study:

• To elucidate the fine structure of beta-2-microglobulin (beta2m) amyloid fibrils.
• To investigate the structural changes and formation mechanisms of beta2m fibrils at different pH values.
• To compare the structural features of beta2m in crystalline and fibrillar states.

Main Methods:

• Solid-state Nuclear Magnetic Resonance (NMR) spectroscopy was employed.
• 2D (13)C-(13)C and (15)N-(13)C correlation experiments were performed.
• Structural analysis was conducted on full-length beta2m fibrils formed at pH 2.5 and pH 7.4.

Main Results:

• Beta-2-microglobulin (beta2m) retains substantial native secondary structure within amyloid fibrils.
• Structural changes primarily affect protein loops, while beta-strands maintain integrity.
• Chemical shift variations at Pro32 suggest cis-trans isomerization is involved in beta2m fibril formation.
• Spectra of fibrils grown at different pH values indicate a conserved fibril architecture.

Conclusions:

• Beta-2-microglobulin amyloid fibrils maintain significant secondary structure.
• Cis-trans isomerization of Pro32 is implicated in the fibril formation process.
• Amyloid species formed under different conditions exhibit a conserved structural architecture.