Molecular heterogeneity of amyloid beta2-microglobulin and modification with advanced glycation end products

Area of Science:

• Biochemistry
• Proteomics
• Medical Science

Background:

• Beta2-microglobulin (beta2m) amyloidosis is a complication in patients undergoing long-term hemodialysis.
• Accumulation of beta2m in amyloid tissues leads to various clinical manifestations.
• Understanding the molecular modifications of beta2m is crucial for elucidating disease pathogenesis.

Purpose of the Study:

• To characterize the molecular heterogeneity of beta2m in amyloid tissue from a hemodialysis patient.
• To investigate the presence and nature of advanced glycation end product (AGE) modification on beta2m.
• To identify specific cleavage sites and cross-linking patterns in modified beta2m species.

Main Methods:

• Liquid chromatography-electrospray ionization mass spectrometry (LC-ESI-MS) for molecular characterization.
• Western blotting to detect protein modifications.
• N-terminal amino acid sequence analysis to identify cleavage sites.

Main Results:

• Amyloid beta2m comprised full-length, truncated, and dimer forms.
• Truncated and dimer beta2m were modified with AGEs, including imidazolone and N(e)-(carboxymethyl)lysine, exhibiting characteristic fluorescence.
• Truncated beta2m species resulted from cleavage at specific amino acid residues (Pro6/Ile7, Gln/Val9, Val9/Tyr10).
• Dimer beta2m species, with molecular masses of 22,591 and 22,675 Da, arose from cross-linking involving truncated beta2m.

Conclusions:

• Beta2m amyloid deposits exhibit significant molecular heterogeneity and AGE modification.
• AGE modification and truncation/dimerization contribute to the structural alterations of beta2m in hemodialysis-associated amyloidosis.
• These findings provide insights into the post-translational modifications of beta2m in amyloid formation.