The Formation of Amyloid-Like Fibrils of alpha-Chymotrypsin in Different Aqueous Organic Solvents

The formation of amyloid-like fibrils of alpha-chymotrypsin was studied in aqueous ethanol, methanol, tert-butanol, dimethylformamide and acetonitrile. Thioflavin T (ThT), Congo red (CR) and 1-anilino-8-naphthalenesulfonic acid (ANS) binding, turbidity, intrinsic fluorescence and far-UV circular dichroism measurements were employed to characterize the amyloid fibril formation. The greatest extent of fibril formation after incubation for 24 h at pH 7.0 and at 24 degrees C was in ethanol at 55%, in methanol and dimethylformamide (DMF) at 60-70% and in tert-butanol at 60-80%. The ANS binding and intrinsic fluorescence results showed that the hydrophobic residues are more solvent-exposed in the aggregated form of alpha-chymotrypsin. The ThT, CR binding and far-UV CD measurements indicated that the formation of the cross-beta structure of alpha-chymotrypsin depends on the polarity of the organic solvent. To determine the role of surface charges in the aggregation, chemically modified forms of alpha-chymotrypsin were prepared. The citraconylated and succinylated enzymes exhibited a higher and the enzyme forms modified with aliphatic aldehydes a lower propensity for aggregation. These results suggest the important role of surface charges in the aggregation of alpha-chymotrypsin