Breakdown of supersaturation barrier links protein folding to amyloid formation

Masahiro Noji,Tatsushi Samejima,Yuji Goto,Yasushi Kawata,Johannes Buchner,József Kardos,Masatomo So,Kensuke Ikenaka,Hideki Mochizuki,Keisuke Yuzu,Yoshihisa Hagihara,Daniel E Otzen,Yoko Akazawa-Ogawa,Keiichi Yamaguchi,Eri Chatani,Vittorio Bellotti

doi:10.1038/s42003-020-01641-6

Abstract

The thermodynamic hypothesis of protein folding, known as the “Anfinsen’s dogma” states that the native structure of a protein represents a free energy minimum determined by the amino acid sequence. However, inconsistent with the Anfinsen’s dogma, globular proteins can misfold to form amyloid fibrils, which are ordered aggregates associated with diseases such as Alzheimer’s and Parkinson’s diseases. Here, we present a general concept for the link between folding and misfolding. We tested the accessibility of the amyloid state for various proteins upon heating and agitation. Many of them showed Anfinsen-like reversible unfolding upon heating, but formed amyloid fibrils upon agitation at high temperatures. We show that folding and amyloid formation are separated by the supersaturation barrier of a protein. Its breakdown is required to shift the protein to the amyloid pathway. Thus, the breakdown of supersaturation links the Anfinsen’s intramolecular folding universe and the intermolecular misfolding universe.

Highlights

The thermodynamic hypothesis of protein folding, known as the “Anfinsen’s dogma” states that the native structure of a protein represents a free energy minimum determined by the amino acid sequence
Amyloid formation was confirmed by circular dichroism (CD) spectroscopy and transmission electron microscopy (TEM) (Fig. 1b and Supplementary Fig. 2b)
The first type of proteins shows a strict dependence on agitation for amyloid formation at high temperatures

Summary

Introduction

The thermodynamic hypothesis of protein folding, known as the “Anfinsen’s dogma” states that the native structure of a protein represents a free energy minimum determined by the amino acid sequence. Inconsistent with the Anfinsen’s dogma, globular proteins can misfold to form amyloid fibrils, which are ordered aggregates associated with diseases such as Alzheimer’s and Parkinson’s diseases. Many of them showed Anfinsen-like reversible unfolding upon heating, but formed amyloid fibrils upon agitation at high temperatures. To test which factors determine the accessibility of the native, unfolded, and amyloid states for a protein, we focused on the breakdown of supersaturation as a critical factor for a pathway to amyloid fibrils. Many of them showed Anfinsen-like reversible unfolding/refolding upon heating, but formed amyloid fibrils with or without agitation at high temperatures. This behavior is explained by the persistence of supersaturation, which depends on the flexibility of denatured states. Reduction of ΔSconf by S–S bonds was estimated by Pace et al50. bAverage hydrophobicity estimated by CamSol44. cThe vacant cells of insulin were not estimated because of the complexity caused by two constituent chains

Methods

Results

Conclusion