Long COVID, which develops following infection with SARS-CoV-2, includes numerous symptoms, and neurological disorders are particularly disruptive to daily life activities. Amyloid fibrils are often implicated in the pathogenesis of neurological disorders, and some fragment peptides derived from SARS-CoV-2, such as spike protein 192-211 (S192), have been reported to form amyloid fibrils. Organic solvents, such as 1,1,1,3,3,3-hexafluoro-2-propanol (HFIP) and dimethyl sulfoxide (DMSO), are widely used to dissolve amyloidogenic peptides; however, they can influence the kinetics of aggregation of the peptide through their initial secondary structure. Therefore, determining how these different solvent environments affect S192 aggregation is important for understanding its structural characteristics. Here, we found that S192 peptide amyloid fibrils exhibit polymorphism under specific solvent conditions. The S192 peptide was dissolved in HFIP, diluted to a final concentration of 2% HFIP, and incubated to form amyloid fibrils with various morphologies. To clarify why the results differed between HFIP and DMSO, we analyzed the FTIR spectra of the S192 peptide dissolved in HFIP or DMSO, which indicated that the secondary structures were constituted differently. In addition, the lag-time for S192 dissolved in HFIP to form amyloids was significantly shorter than that in DMSO. These results are consistent with the hypothesis that rapid amyloid fibril formation may correlate with heterogeneous fibril morphology. Moreover, we examined hemagglutination to determine the functional significance of the polymorphism in the S192 amyloid fibrils. The results showed that amyloid fibrils formed from the S192 peptide dissolved in HFIP exhibited polymorphism and demonstrated higher hemagglutination activity than those in DMSO, which exhibited a single morphology.
