title: Off-pathway aggregation can inhibit fibrillation at high protein concentrations.
abstract: Ribosomal protein S6 fibrillates readily at slightly elevated temperatures and acidic pH. We find that S6 fibrillation is retarded rather than favored when the protein concentration is increased above a threshold concentration of around 3.5mg/mL. We name this threshold concentration C(FR), the concentration at which fibrillation is retarded. Our data are consistent with a model in which this inhibition is due to the formation of an off-pathway oligomeric species with native-like secondary structure. The oligomeric species dominates at high protein concentrations but exists in dynamic equilibrium with the monomer so that seeding with fibrils can overrule oligomer formation and favors fibrillation under C(FR) conditions. Thus, fibrillation competes with formation of off-pathway oligomers, probably due to a monomeric conversion step that is required to commit the protein to the fibrillation pathway. The S6 oligomer is resistant to pepsin digestion. We also report that S6 forms different types of fibrils dependent on protein concentration. Our observations highlight the multitude of conformational states available to proteins under destabilizing conditions.
authors: Center for Insoluble Protein Structures (inSPIN), Interdisciplinary Nanoscience Center (iNANO), Department of Molecular Biology and Genetics, University of Aarhus, Gustav Wieds Vej 14, DK-8000 Aarhus C, Denmark. taru.deva@gmail.com
authors: Taru
authors: T
authors: Deva
authors: Nikolai
authors: N
authors: Lorenzen
authors: Brian S
authors: BS
authors: Vad
authors: Steen V
authors: SV
authors: Petersen
authors: Ida
authors: I
authors: Thørgersen
authors: Jan J
authors: JJ
authors: Enghild
authors: Torsten
authors: T
authors: Kristensen
authors: Daniel E
authors: DE
authors: Otzen
mesh_terms: D002942:Circular Dichroism; D004591:Electrophoresis, Polyacrylamide Gel; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D018625:Microscopy, Atomic Force; D008956:Models, Chemical; D008958:Models, Molecular; D009154:Mutation; D011487:Protein Conformation; D055503:Protein Multimerization; D059748:Proteolysis; D019893:Ribosomal Protein S6 Kinases / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D017550:Spectroscopy, Fourier Transform Infrared; D013696:Temperature; D013997:Time Factors
chemical_list: D019893:Ribosomal Protein S6 Kinases