Aggregation and Fibril Morphology of the Arctic Mutation of Alzheimer’s Aβ peptide by CD, TEM, STEM and in situ AFM

• Published in: Journal of Structural Biology
• Main Authors: Norlin, Nils, Hellberg, Magnus, Filippov, Andrei, Sousa, Alioscka A., Gröbner, Gerhard, Leapman, Richard D., Almqvist, Nils, Antzutkin, Oleg N.
• Format: Text
• Language: English
• Published: 2012
• Subjects: Article; Arctic
• Online Access: http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3466396; http://www.ncbi.nlm.nih.gov/pubmed/22750418; https://doi.org/10.1016/j.jsb.2012.06.010

Morphology of aggregation intermediates, polymorphism of amyloid fibrils and aggregation kinetics of the “Arctic” mutant of the Alzheimer’s amyloid β-peptide, Aβ(1-40)(E22G), in a physiologically relevant TRIS buffer (pH 7.4) were thoroughly explored in comparison with the human wild type Alzheimer’s amyloid peptide, wt-Aβ(1-40), using both in situ atomic force and electron microscopy, circular dichroism and thioflavin T fluorescence assays. For arc-Aβ(1-40) at the end of the ‘lag’-period of fibrillization an abrupt appearance of ~3 nm size ‘spherical aggregates’ with a homogeneous morphology, was identified. Then, the aggregation proceeds with a rapid growth of amyloid fibrils with a variety of morphologies, while the spherical aggregates eventually disappeared during in situ measurements. Arc-Aβ(1-40) was also shown to form fibrils at much lower concentrations than wt-Aβ(1-40): ≤2.5 μM and 12.5 μM, respectively. Moreover, at the same concentration, 50 μM, the aggregation process proceeds more rapidly for arc-Aβ(1-40): The first amyloid fibrils were observed after ca 72 hours from the onset of incubation as compared to approximately 7 days for wt-Aβ(1-40). Amyloid fibrils of arc-Aβ(1-40) exhibit a large variety of polymorphs, at least five, both coiled and non-coiled distinct fibril structures were recognized by AFM, while at least four types of arc-Aβ(1-40) fibrils were identified by TEM and STEM and their mass-per-length statistics were collected suggesting supramolecular structures with two, four and six β-sheet laminae. Our results suggest a pathway of fibrillogenesis for full-length Alzheimer’s peptides with small and structurally ordered transient spherical aggregates as on-pathway immediate precursors of amyloid fibrils.