title: The roles of turn formation and cross-strand interactions in fibrillization of peptides derived from the OspA single-layer beta-sheet.
abstract: We previously demonstrated that a beta-hairpin peptide, termed BH(9-10), derived from a single-layer beta-sheet of Borrelia OspA protein, formed a native-like beta-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 beta-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 alpha-to-beta 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 beta-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.
authors.affiliation: Department of Biochemistry and Biophysics, University of Rochester Medical Center, Rochester, New York 14642, USA.
authors.forename: S
authors.initials: S
authors.lastname: Ohnishi
authors.forename: A
authors.initials: A
authors.lastname: Koide
authors.forename: S
authors.initials: S
authors.lastname: Koide
mesh_terms: D000954:Antigens, Surface / Q000737:chemistry* / Q000378:metabolism; D001425:Bacterial Outer Membrane Proteins / Q000737:chemistry* / Q000378:metabolism; D001426:Bacterial Proteins / Q000737:chemistry* / Q000378:metabolism; D001428:Bacterial Vaccines; D001898:Borrelia / Q000737:chemistry*; D011232:Chemical Precipitation; D007700:Kinetics; D008074:Lipoproteins; D022123:Lyme Disease Vaccines / Q000737:chemistry* / Q000378:metabolism; D008958:Models, Molecular; D010455:Peptides / Q000737:chemistry / Q000378:metabolism; D017433:Protein Structure, Secondary
chemical_list: D000954:Antigens, Surface; D001425:Bacterial Outer Membrane Proteins; D001426:Bacterial Proteins; D001428:Bacterial Vaccines; D008074:Lipoproteins; D022123:Lyme Disease Vaccines; C072045:OspA protein; D010455:Peptides