Supersaturation-limited amyloid fibrillation of insulin revealed by ultrasonication.
Amyloid fibrils form in supersaturated solutions via a nucleation and growth mechanism. We proposed that ultrasonication may be an effective agitation to trigger nucleation that would otherwise not occur under the persistent metastability of supersaturation. However, the roles of supersaturation and effects of ultrasonication have not been elucidated in detail except for limited cases. Insulin is an amyloidogenic protein that is useful for investigating the mechanisms underlying amyloid fibrillation with biological relevance. We studied the alcohol-induced amyloid fibrillation of insulin using various concentrations of 2,2,2-trifluoroethanol and 1,1,1,3,3,3-hexafluoro-2-propanol at pH 2.0 and 4.8. Ultrasonic irradiation effectively triggered fibrillation under conditions in which insulin retained persistent supersaturation. Structural analyses by circular dichroism, Fourier transform infrared spectroscopy, transmission electron microscopy, and atomic force microscopy revealed that the dominant structures of fibrils varied between parallel and antiparallel β-sheets depending on the solvent conditions. pH and alcohol concentration-dependent phase diagrams showed a marked difference before and after the ultrasonic treatment, which indicated that the persistent metastability of supersaturation determined the conformations of insulin. These results indicate the importance of an alternative view of amyloid fibrils as supersaturation-limited crystal-like aggregates formed above the solubility limit.
From the Institute for Protein Research, Osaka University, Yamadaoka 3-2, Suita, Osaka 565-0871, Japan and.
Hiroya
H
Muta
From the Institute for Protein Research, Osaka University, Yamadaoka 3-2, Suita, Osaka 565-0871, Japan and.
Young-Ho
YH
Lee
the Department of Biochemistry, Eötvös Loránd University, Pázmány sétány 1/C, Budapest 1117, Hungary.
József
J
Kardos
From the Institute for Protein Research, Osaka University, Yamadaoka 3-2, Suita, Osaka 565-0871, Japan and.
Yuxi
Y
Lin
From the Institute for Protein Research, Osaka University, Yamadaoka 3-2, Suita, Osaka 565-0871, Japan and.
Hisashi
H
Yagi
From the Institute for Protein Research, Osaka University, Yamadaoka 3-2, Suita, Osaka 565-0871, Japan and ygoto@protein.osaka-u.ac.jp.
Yuji
Y
Goto
D000682:Amyloid / Q000737:chemistry*; D002942:Circular Dichroism; D006863:Hydrogen-Ion Concentration; D007328:Insulin / Q000737:chemistry*; D007700:Kinetics; D011487:Protein Conformation / Q000528:radiation effects; D017510:Protein Folding / Q000528:radiation effects; D012995:Solubility; D014465:Ultrasonics
D000682:Amyloid; D007328:Insulin
Alcohol; Amyloid; Circular Dichroism (CD); Electron Microscopy (EM); Fourier Transform IR (FTIR); Insulin; Protein Aggregation; Protein Misfolding; Supersaturation; Ultrasonication