Structural and conformational variants of human β2-microglobulin characterized by capillary electrophoresis and complementary separation methods

The small (Mr=11 729) serum protein β2-microglobulin is prone to precipitate as amyloid in a protein conformational disorder (PCD) that occurs in a significant number of patients on chronic hemodialysis. Analyses by capillary electrophoresis (CE) were undertaken to study β2-microglobulin conformations under native separation conditions and showed an apparent heterogeneity of purified preparations when the sample matrix included organic solvents such as acetonitrile, trifluoroethanol and ethanol. We here present LC–MS, CE–MS, and CE studies of changes of separation profiles as a function of capillary temperature, organic solvent concentration, and analysis time. The results suggest that the apparent β2-microglobulin heterogeneity observed by CE is caused by two distinct protein conformations that are present in β2-microglobulin under partly denaturing conditions and that Met99-oxidized and normal (i.e. nonoxidized) β2-microglobulin behave similarly with respect to the potential to attain this alternative conformation. CE is an attractive method to study early and intermediate soluble folding variants that may be involved in PCDs and CE thus may have an important role as a tool for understanding other PCDs characterized by amyloid deposition.