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The roles of turn formation and cross-strand interactions in fibrillization of peptides derived from the OspA single-layer ß-sheet

Department of Biochemistry and Biophysics, University of Rochester Medical Center, Rochester, New York 14642, USA

Reprint requests to: Shohei Koide, Department of Biochemistry and Biophysics, Box 712, University of Rochester Medical Center, Rochester, NY 14642, USA; e-mail: Shohei_Koide{at}urmc.rochester.edu; fax: (716) 275-6007.

We previously demonstrated that a ß-hairpin peptide, termed BH^9–10, derived from a single-layer ß-sheet of Borrelia OspA protein, formed a native-like ß-turn in trifluoroethanol (TFE) solution, and it assembled into amyloid-like fibrils at higher TFE concentrations. This peptide is highly charged, and fibrillization of such a hydrophilic peptide is quite unusual. In this study, we designed a circularly permutated peptide of BH^9–10, termed BH^10–9. When folded into their respective ß-hairpin structures found in OspA, these peptides would have identical cross-strand interactions but different turns connecting the strands. NMR study revealed that BH^10–9 had little propensity to form a turn structure both in aqueous and TFE solutions. At higher TFE concentration, BH^10–9 precipitated with a concomitant -to-ß conformational conversion, in a similar manner to the BH^9–10 fibrillization. However, the BH^10–9 precipitates were nonfibrillar aggregation. The precipitation kinetics of BH^10–9 was exponential, consistent with a first-order molecular assembly reaction, while the fibrillization of BH^9–10 showed sigmoidal kinetics, indicative of a two-step reaction consisting of nucleation and molecular assembly. The correlation between native-like turn formation and fibrillization of our peptide system strongly suggests that BH^9–10 adopts a native-like ß-hairpin conformation in the fibrils. Remarkably, seeding with the preformed BH^10–9 precipitates changed the two-step BH^9–10 fibrillization to a one-step molecular assembly reaction, and disrupted the BH^9–10 fibril structure, indicating interactions between the BH^10–9 aggregates and the BH^9–10 peptide. Our results suggest that, in these peptides, cross-strand interactions are the driving force for molecular assembly, and turn formation limits modes of peptide assembly.

Keywords: ß-Sheet; ß-hairpin; peptide design; folding; fibril formation

Abbreviations: CD, circular dichroism • HSQC, heteronuclear single quantum coherence • NMR, nuclear magnetic resonance • NOE, nuclear Overhauser effect • NOESY, NOE spectroscopy • OspA, outer surface protein A • PCR, polymerase chain reaction • TFE, trifluoroethanol • TOCSY, total correlation spectroscopy

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