The deposition of amyloid fibrils is associated with the pathology of more than 30 disorders. α-Synuclein (α-syn) consisting of a 140-residue is an intrinsically disordered protein that is linked to Parkinson’s disease neuropathologically. Recently, Cremers et al. reported that polyphosphate (polyP) accelerated the amyloid fibrillation of several amyloidogenic proteins, though the mechanism of polyP-induced amyloid fibrillation is not well understood. In this study, we investigated the effects of polyPs with different chain lengths on the amyloid fibrillation of α-syn under the ultrasonication. We found that the fibrillation of α-syn was significantly accelerated depending on the chain length and concentration of polyPs. Intriguingly, long-chain polyPs revealed the two optimum concentrations for the fibrillation; low and high concentrations. These promoting effects for the fibrillation were interpreted by the charge interaction with the protein and the salting-out effects of polyP under the ultrasonication. These results suggest an important role of biopolymer on amyloid fibrillation in vivo.
