Molecular heterogeneity of amyloid β2-microglobulin and modification with advanced glycation end products

By using liquid chromatography–electrospray ionization mass spectrometry, Western blotting and N-terminal amino acid sequence analysis, we characterized the molecular heterogeneity and advanced glycation end product (AGE) modification of β2-microglobulin (β2m) extracted from the amyloid tissue of a hemodialysis patient. Amyloid β2m was composed of full-length β2m, truncated β2m and dimer β2m. Truncated β2m and dimer β2m were modified with AGEs such as imidazolone and Nϵ-(carboxymethyl)lysine, and showed fluorescence characteristic of AGE. Truncated β2m species were formed by cleavage between amino acid residues of Pro6/Ile7, Gln8/Val9 and Val9/Tyr10. Heterogeneous dimer β2m species showed the molecular masses of 22 591 and 22 675, which resulted from cross-linking between truncated β2m.