Mutational analysis of the propensity for amyloid formation by a globular protein.

Acylphosphatase can be converted in vitro, by addition of trifluoroethanol (TFE), into amyloid fibrils of the type observed in a range of human diseases. The propensity to form fibrils has been investigated for a series of mutants of acylphosphatase by monitoring the range of TFE concentrations that result in aggregation. We have found that the tendency to aggregate correlates inversely with the conformational stability of the native state of the protein in the different mutants. In accord with this, the most strongly destabilized acylphosphatase variant forms amyloid fibrils in aqueous solution in the absence of TFE. These results show that the aggregation process that leads to amyloid deposition takes place from an ensemble of denatured conformations under conditions in which non-covalent interactions are still favoured. These results support the hypothesis that the stability of the native state of globular proteins is a major factor preventing the in vivo conversion of natural proteins into amyloid fibrils under non-pathological conditions. They also suggest that stabilizing the native states of amyloidogenic proteins could aid prevention of amyloidotic diseases.