title: Amorphous Aggregation of Cytochrome c with Inherently Low Amyloidogenicity Is Characterized by the Metastability of Supersaturation and the Phase Diagram.
abstract: Despite extensive studies on the folding and function of cytochrome c, the mechanisms underlying its aggregation remain largely unknown. We herein examined the aggregation behavior of the physiologically relevant two types of cytochrome c, metal-bound cytochrome c, and its fragment with high amyloidogenicity as predicted in alcohol/water mixtures. Although the aggregation propensity of holo cytochrome c was low due to high solubility, markedly unfolded apo cytochrome c, lacking the heme prosthetic group, strongly promoted the propensity for amorphous aggregation with increases in hydrophobicity. Silver-bound apo cytochrome c increased the capacity of fibrillar aggregation (i.e., protofibrils or immature fibrils) due to subtle structural changes of apo cytochrome c by strong binding of silver. However, mature amyloid fibrils were not detected for any of the cytochrome c variants or its fragment, even with extensive ultrasonication, which is a powerful amyloid inducer. These results revealed the intrinsically low amyloidogenicity of cytochrome c, which is beneficial for its homeostasis and function by facilitating the folding and minimizing irreversible amyloid formation. We propose that intrinsically low amyloidogenicity of cytochrome c is attributed to the low metastability of supersaturation. The phase diagram constructed based on solubility and aggregate type is useful for a comprehensive understanding of protein aggregation. Furthermore, amorphous aggregation, which is also viewed as a generic property of proteins, and amyloid fibrillation can be distinguished from each other by the metastability of supersaturation.
authors.affiliation: Institute for Protein Research, Osaka University , Yamadaoka 3-2, Suita, Osaka 565-0871, Japan.
authors.forename: Yuxi
authors.initials: Y
authors.lastname: Lin
authors.affiliation: MTA-ELTE NAP B Neuroimmunology Research Group, Department of Biochemistry, Eötvös Loránd University , Budapest H-1117, Hungary.
authors.forename: József
authors.initials: J
authors.lastname: Kardos
authors.affiliation: Graduate School of Chemical Sciences and Engineering, Hokkaido University , Kita 13, Nishi 8, Kita-ku, Sapporo 060-8628, Japan.
authors.forename: Mizue
authors.initials: M
authors.lastname: Imai
authors.affiliation: Institute for Protein Research, Osaka University , Yamadaoka 3-2, Suita, Osaka 565-0871, Japan.
authors.forename: Tatsuya
authors.initials: T
authors.lastname: Ikenoue
authors.affiliation: Institute for Protein Research, Osaka University , Yamadaoka 3-2, Suita, Osaka 565-0871, Japan.
authors.forename: Misaki
authors.initials: M
authors.lastname: Kinoshita
authors.affiliation: Institute for Protein Research, Osaka University , Yamadaoka 3-2, Suita, Osaka 565-0871, Japan.
authors.forename: Toshihiko
authors.initials: T
authors.lastname: Sugiki
authors.affiliation: Graduate School of Chemical Sciences and Engineering, Hokkaido University , Kita 13, Nishi 8, Kita-ku, Sapporo 060-8628, Japan.
authors.forename: Koichiro
authors.initials: K
authors.lastname: Ishimori
authors.affiliation: Institute for Protein Research, Osaka University , Yamadaoka 3-2, Suita, Osaka 565-0871, Japan.
authors.forename: Yuji
authors.initials: Y
authors.lastname: Goto
authors.affiliation: Institute for Protein Research, Osaka University , Yamadaoka 3-2, Suita, Osaka 565-0871, Japan.
authors.forename: Young-Ho
authors.initials: YH
authors.lastname: Lee