Monitoring the prevention of amyloid fibril formation by alpha-crystallin. Temperature dependence and the nature of the aggregating species.

The molecular chaperone, alpha-crystallin, has the ability to prevent the fibrillar aggregation of proteins implicated in human diseases, for example, amyloid beta peptide and alpha-synuclein. In this study, we examine, in detail, two aspects of alpha-crystallin's fibril-suppressing ability: (a) its temperature dependence, and (b) the nature of the aggregating species with which it interacts. First, the efficiency of alpha-crystallin to suppress fibril formation in kappa-casein and alpha-synuclein increases with temperature, despite their rate of fibrillation also increasing in the absence of alpha-crystallin. This is consistent with an increased chaperone ability of alpha-crystallin at higher temperatures to protect target proteins from amorphous aggregation [GB Reddy, KP Das, JM Petrash & WK Surewicz (2000) J Biol Chem275, 4565-4570]. Second, dual polarization interferometry was used to monitor real-time alpha-synuclein aggregation in the presence and absence of alphaB-crystallin. In contrast to more common methods for monitoring the time-dependent formation of amyloid fibrils (e.g. the binding of dyes like thioflavin T), dual polarization interferometry data did not reveal any initial lag phase, generally attributed to the formation of prefibrillar aggregates. It was shown that alphaB-crystallin interrupted alpha-synuclein aggregation at its earliest stages, most likely by binding to partially folded monomers and thereby preventing their aggregation into fibrillar structures.