Amyloid fibril formation by a normally folded protein in the absence of denaturants and agitation.

The conversion of normally folded proteins into amyloid-like fibrils is an important process in protein chemistry, biology, pathology and biotechnology. This process generally requires harsh conditions, such as pH extremes, organic cosolvents, high temperatures, high pressures or shear forces. Such conditions promote aggregation because they partially unfold structured proteins or allow the sampling of locally unfolded native-like states, both of which possibly represent amyloidogenic states. Here we report the formation of amyloid-like fibrils by the lipase from Pseudomonas sp. under conditions that are close to physiological, that is, in the absence of denaturants and agitation. The resulting aggregates bind thioflavin T and Congo red, causing their characteristic spectral changes observed in the presence of amyloid fibrils. They possess a significant quantity of β-sheet structure, as detected with Fourier transform infrared and far-UV circular dichroism spectroscopies, and appear fibrillar using transmission electron microscopy. These results indicate that the lipase from Pseudomonas sp. can be a useful model system for the characterization of a key process, such as amyloid fibril formation under physiological conditions.