From the same paper:
"Many of the characteristics of proteins that enable the avoidance of aggregation, and amyloid formation in particular, are encoded by their amino acid sequences116. The elucidation of this code has enabled the identification of factors that determine the intrinsic aggregation propensity of these molecules117, 118, 119. Hence, it has been realized that globular proteins fold into structures that sequester aggregation-prone regions in their interior; in addition, typical features of the folding process, such as very high cooperativity, generate considerable kinetic barriers to the conversion of folded proteins into aggregation-prone species50, 120. Furthermore, specific patterns of residues, such as alternating hydrophobic–hydrophilic stretches50, 121, that tend to favour the amyloid state are commonly selected against during evolution119, 121, 122 or are otherwise neutralized by the insertion of highly aggregation-resistant residues, which are known as 'gatekeepers' (Refs 50,123).
Other protective mechanisms against amyloid formation are associated with properties of the cellular environment, including the location of proteins within specific compartments124, 125, and the presence of a multitude of molecular chaperones and degradation processes, such as the ubiquitin–proteasome126, 127, 128 and the autophagy129, 130, 131 systems, which function to prevent the formation and accumulation of misfolded and aggregated polypeptide chains11, 132. Indeed, the major genetic risk factor for late-onset Alzheimer's disease is the presence of an apolipoprotein E variant that reduces the ability of cells to degrade the amyloid-β peptide133."