Heat-induced conversion of beta(2)-microglobulin and hen egg-white lysozyme into amyloid fibrils.
Thermodynamic parameters characterizing protein stability can be obtained for a fully reversible folding/unfolding system directly by differential scanning calorimetry (DSC). However, the reversible DSC profile can be altered by an irreversible step causing aggregation. Here, to obtain insight into amyloid fibrils, ordered and fibrillar aggregates responsible for various amyloidoses, we studied the effects on human beta(2)-microglobulin and hen egg-white lysozyme of a combination of agitation and heating. Aggregates formed by mildly agitating protein solutions in the native state in the presence of NaCl were heated in the cell of the DSC instrument. For beta(2)-microglobulin, with an increase in the concentration of NaCl at neutral pH, the thermogram began to show an exothermic transition accompanied by a large decrease in heat capacity, followed by a kinetically controlled thermal response. Similarly, the aggregated lysozyme at a high concentration of NaCl revealed a similar distinct transition in the DSC thermogram over a wide pH range. Electron microscopy demonstrated the conformational change into amyloid fibrils. Taken together, the combined use of agitation and heating is a powerful way to generate amyloid fibrils from two proteins, beta(2)-microglobulin and hen egg-white lysozyme, and to evaluate the effects of heat on fibrillation, in which the heat capacity is crucial to characterizing the transition.
Institute for Protein Research, Osaka University and CREST, Japan Science and Technology Agency, Yamadaoka 3-2, Suita, Osaka 565-0871, Japan.
Kenji
K
Sasahara
Institute for Protein Research, Osaka University and CREST, Japan Science and Technology Agency, Yamadaoka 3-2, Suita, Osaka 565-0871, Japan.
Hisashi
H
Yagi
Faculty of Medical Sciences, University of Fukui and CREST, Japan Science and Technology Agency, Eiheiji, Fukui 910-1193, Japan.
Hironobu
H
Naiki
Institute for Protein Research, Osaka University and CREST, Japan Science and Technology Agency, Yamadaoka 3-2, Suita, Osaka 565-0871, Japan. Electronic address: ygoto@protein.osaka-u.ac.jp.
Yuji
Y
Goto
D000682:Amyloid / Q000737:chemistry* / Q000378:metabolism / Q000648:ultrastructure; D000818:Animals; D002151:Calorimetry; D002645:Chickens; D002942:Circular Dichroism; D004527:Egg Proteins / Q000737:chemistry* / Q000378:metabolism / Q000648:ultrastructure; D006358:Hot Temperature; D006801:Humans; D009113:Muramidase / Q000737:chemistry* / Q000378:metabolism / Q000648:ultrastructure; D011487:Protein Conformation; D013816:Thermodynamics; D001613:beta 2-Microglobulin / Q000737:chemistry* / Q000378:metabolism / Q000648:ultrastructure
D000682:Amyloid; D004527:Egg Proteins; D001613:beta 2-Microglobulin; D009113:Muramidase