Congophilicity (Congo red affinity) of different β2-microglobulin conformations characterized by dye affinity capillary electrophoresis

The amyloidogenic protein β2-microglobulin was characterized by affinity capillary electrophoresis (CE). CE could separate conformational variants of β2-microglobulin and with the amyloid-specific dye Congo red as a buffer additive it was possible to measure different Congo red-affinities of native and abnormally folded β2-microglobulin. We find that native β2-microglobulin has an intermediate affinity for Congo red at pH 7.3 and that binding involves electrostatic interactions. The conformational variant of β2-microglobulin that appears in acetonitrile solutions binds Congo red more strongly. Affinity CE using Congo red as a buffer additive is a new, simple, fast, and quantitative micromethod for the characterization of soluble conformational intermediates of amyloidogenic proteins.