title: Supersaturation-limited and Unlimited Phase Transitions Compete to Produce the Pathway Complexity in Amyloid Fibrillation.
abstract: Although amyloid fibrils and amorphous aggregates are two types of aggregates formed by denatured proteins, their relationship currently remains unclear. We used β2-microglobulin (β2m), a protein responsible for dialysis-related amyloidosis, to clarify the mechanism by which proteins form either amyloid fibrils or amorphous aggregates. When ultrasonication was used to accelerate the spontaneous fibrillation of β2m at pH 2.0, the effects observed depended on ultrasonic power; although stronger ultrasonic power effectively accelerated fibrillation, excessively strong ultrasonic power decreased the amount of fibrils formed, as monitored by thioflavin T fluorescence. An analysis of the products formed indicated that excessively strong ultrasonic power generated fibrillar aggregates that retained β-structures but without high efficiency as seeds. On the other hand, when the spontaneous fibrillation of β2m was induced at higher concentrations of NaCl at pH 2.0 with stirring, amorphous aggregates became more dominant than amyloid fibrils. These apparent complexities in fibrillation were explained comprehensively by a competitive mechanism in which supersaturation-limited reactions competed with supersaturation-unlimited reactions. We link the kinetics of protein aggregation and a conformational phase diagram, in which supersaturation played important roles.
authors.affiliation: Institute for Protein Research, Osaka University, Yamadaoka 3-2, Suita, Osaka 565-0871, Japan.
authors.forename: Masayuki
authors.initials: M
authors.lastname: Adachi
authors.affiliation: Institute for Protein Research, Osaka University, Yamadaoka 3-2, Suita, Osaka 565-0871, Japan.
authors.forename: Masatomo
authors.initials: M
authors.lastname: So
authors.affiliation: High Pressure Protein Research Center, Institute for Advanced Technology, Kinki University, 930 Nishimitani, Kinokawa, Wakayama 649-6493, Japan.
authors.forename: Kazumasa
authors.initials: K
authors.lastname: Sakurai
authors.affiliation: Department of Biochemistry and MTA-ELTE NAP B Neuroimmunology Research Group, Eötvös Loránd University, Pázmány sétány 1/C, Budapest, 1117, Hungary.
authors.forename: József
authors.initials: J
authors.lastname: Kardos
authors.affiliation: Institute for Protein Research, Osaka University, Yamadaoka 3-2, Suita, Osaka 565-0871, Japan. Electronic address: ygoto@protein.osaka-u.ac.jp.
authors.forename: Yuji
authors.initials: Y
authors.lastname: Goto
mesh_terms: D000682:Amyloid / Q000737:chemistry* / Q000648:ultrastructure; D003460:Crystallization; D006801:Humans; D007700:Kinetics; D044367:Phase Transition; D066329:Protein Aggregates; D017433:Protein Structure, Secondary; D012492:Salts / Q000737:chemistry; D013010:Sonication; D001613:beta 2-Microglobulin / Q000737:chemistry* / Q000648:ultrastructure
chemical_list: D000682:Amyloid; D066329:Protein Aggregates; D012492:Salts; D001613:beta 2-Microglobulin
keywords: aggregation; amyloid; crystallization; glass transition; protein aggregation; protein conformation; protein misfolding; solubility; ultrasonication