Solution conformation and amyloid-like fibril formation of a polar peptidederived from a beta-hairpin in the OspA single-layer beta-sheet

A 23-residue peptide termed wBH(9-10) was designed based on a beta-hairpin segment of the single-layer beta-sheet region of Borrelia OspA protein. The peptide contains a large number of charged amino acid residues, and it doe s not follow the amphipathic pattern that is commonly found in natural beta -sheets. In aqueous solution, the peptide was highly soluble and flexible, with a propensity to form a non-native beta-turn. Trifluoroethanol (TFE) st abilized a native-like beta-turn in BH9-10. TFE also decreased the level of solubility of the peptide, resulting in peptide precipitation. The precipi tation process accompanied a conformational conversion to a beta-sheet stru cture, as judged with circular dichroism spectroscopy. The precipitate was found to be fibrils similar to those associated with human amyloid diseases . The fibrillization kinetics depended on peptide and TFE concentrations, a nd had a nucleation step followed by an assembly step. The fibrillization w as reversible, and the dissociation reaction involved two phases. TFE appea rs to induce the fibrils by stabilizing a beta-sheet conformation of the pe ptide that optimally satisfies hydrogen bonding and electrostatic complemen tarity. This TFE-induced fibrillization is quite unusual, because most amyl oidogenic peptides form fibrils in aqueous solution and TFE disrupts these fibrils. Nevertheless, the BH9-10 fibrils have similar structure to other f ibrils, supporting the emerging idea that polypeptides possess an intrinsic ability to form amyloid-like fibrils. The high level of solubility of BH9- 10, the ability to precisely control fibril formation and dissociation, and the high-resolution structure of the same sequence in the beta-hairpin con formation in the OspA protein provide a tractable experimental system for s tudying the fibril formation mechanism. (C) 2000 Academic Press.