title: Amyloid formation of a protein in the absence of initial unfolding and destabilization of the native state.
abstract: In 5% (v/v) trifluoroethanol, pH 5.5, 25 degrees C one of the acylphosphatases from Drosophila melanogaster (AcPDro2) forms fibrillar aggregates that bind thioflavin T and Congo red and have an extensive beta-sheet structure, as revealed by circular dichroism. Atomic force microscopy indicates that the fibrils and their constituent protofilaments have diameters compatible with those of natural amyloid fibrils. Spectroscopic and biochemical investigation, carried out using near- and far-UV circular dichroism, intrinsic and 1-anilino-8-naphthalenesulfonic acid-derived fluorescence, dynamic light scattering, and enzymatic activity assays, shows that AcPDro2 has, before aggregation, a secondary structure content packing around aromatic and hydrophobic residues, hydrodynamic diameter, and catalytic activity indistinguishable from those of the native protein. The native protein was found to have the same conformational stability under native and aggregating conditions, as determined from urea-induced unfolding. The kinetic analysis supports models in which AcPDro2 aggregates initially without need to unfold and subsequently undergoes a conformational change into amyloid-like structures. Although fully or partially unfolded states have a higher propensity to aggregate, the residual aggregation potential that proteins maintain upon complete folding can be physiologically relevant and be directly involved in the pathogenesis of some protein deposition diseases.
authors.affiliation: Dipartimento di Scienze Biochimiche, Università di Firenze, Firenze, Italy.
authors.forename: Gemma
authors.initials: G
authors.lastname: Soldi
authors.forename: Francesco
authors.initials: F
authors.lastname: Bemporad
authors.forename: Silvia
authors.initials: S
authors.lastname: Torrassa
authors.forename: Annalisa
authors.initials: A
authors.lastname: Relini
authors.forename: Matteo
authors.initials: M
authors.lastname: Ramazzotti
authors.forename: Niccolò
authors.initials: N
authors.lastname: Taddei
authors.forename: Fabrizio
authors.initials: F
authors.lastname: Chiti
mesh_terms: D017766:Acid Anhydride Hydrolases / Q000737:chemistry*; D000682:Amyloid / Q000032:analysis / Q000138:chemical synthesis* / Q000648:ultrastructure*; D001665:Binding Sites; D029721:Drosophila Proteins / Q000737:chemistry*; D004789:Enzyme Activation; D004795:Enzyme Stability; D046912:Multiprotein Complexes / Q000032:analysis / Q000138:chemical synthesis; D011485:Protein Binding; D011487:Protein Conformation; D011489:Protein Denaturation; D017510:Protein Folding; D000097024:Acylphosphatase
chemical_list: D017766:Acid Anhydride Hydrolases; D000682:Amyloid; D029721:Drosophila Proteins; D046912:Multiprotein Complexes; D000097024:Acylphosphatase