title: Structural insights into Aβ42 oligomers using site-directed spin labeling.
abstract: Oligomerization of the 42-residue peptide Aβ42 plays a key role in the pathogenesis of Alzheimer disease. Despite great academic and medical interest, the structures of these oligomers have not been well characterized. Site-directed spin labeling combined with electron paramagnetic resonance spectroscopy is a powerful approach for studying structurally ill-defined systems, but its application in amyloid oligomer structure study has not been systematically explored. Here we report a comprehensive structural study on a toxic Aβ42 oligomer, called globulomer, using site-directed spin labeling complemented by other techniques. Transmission electron microscopy shows that these oligomers are globular structures with diameters of ∼7-8 nm. Circular dichroism shows primarily β-structures. X-ray powder diffraction suggests a highly ordered intrasheet hydrogen-bonding network and a heterogeneous intersheet packing. Residue-level mobility analysis on spin labels introduced at 14 different positions shows a structured state and a disordered state at all labeling sites. Side chain mobility analysis suggests that structural order increases from N- to C-terminal regions. Intermolecular distance measurements at 14 residue positions suggest that C-terminal residues Gly-29-Val-40 form a tightly packed core with intermolecular distances in a narrow range of 11.5-12.5 Å. These intermolecular distances rule out the existence of fibril-like parallel in-register β-structures and strongly suggest an antiparallel β-sheet arrangement in Aβ42 globulomers.
authors.affiliation: Department of Neurology, Brain Research Institute, Molecular Biology Institute, UCLA, Los Angeles, California 90095, USA.
authors.forename: Lei
authors.initials: L
authors.lastname: Gu
authors.forename: Cong
authors.initials: C
authors.lastname: Liu
authors.forename: Zhefeng
authors.initials: Z
authors.lastname: Guo
mesh_terms: D000544:Alzheimer Disease / Q000378:metabolism; D016229:Amyloid beta-Peptides / Q000737:chemistry*; D000818:Animals; D002470:Cell Survival; D002942:Circular Dichroism; D004578:Electron Spin Resonance Spectroscopy / Q000379:methods*; D006367:HeLa Cells; D006801:Humans; D046529:Microscopy, Electron, Transmission; D016716:PC12 Cells; D010446:Peptide Fragments / Q000737:chemistry*; D017510:Protein Folding; D017433:Protein Structure, Secondary; D051381:Rats; D013113:Spin Labels; D013778:Tetrazolium Salts; D013844:Thiazoles; D014961:X-Ray Diffraction
chemical_list: D016229:Amyloid beta-Peptides; D010446:Peptide Fragments; D013113:Spin Labels; D013778:Tetrazolium Salts; D013844:Thiazoles; C075222:amyloid beta-protein (1-42); C022616:thiazolyl blue
keywords: Alzheimer Disease; Amyloid; EPR; ESR; Electron Paramagnetic Resonance; Protein Aggregation; Protein Misfolding; Protein Self-assembly; Spin Labeling