Mixtures of Wild-type and a Pathogenic (E22G) Form of A beta 40 in Vitro Accumulate Protofibrils, Including Amyloid Pores

• Published in: Journal of molecular biology 2003-09, Vol.332 (4), p.795-808
• Main Authors: Lashuel, HA, Hartley, D M, Petre, B M, Wall, J S, Simon, M N, Walz, T, Lansbury, PT Jr
• Format: Article
• Language: English
• ISSN: 0022-2836
• DOI: 10.1016/S0022-2836(03)00927-6

Although APP mutations associated with inherited forms of Alzheimer's disease (AD) are relatively rare, detailed studies of these mutations may prove critical for gaining important insights into the mechanism(s) and etiology of AD. Here, we present a detailed biophysical characterization of the structural properties of protofibrils formed by the Arctic variant (E22G) of amyloid- beta protein (A beta 40ARC) as well as the effect of A beta 40WT on the distribution of the protofibrillar species formed by A beta 40ARC by characterizing biologically relevant mixtures of both proteins that may mimic the situation in the heterozygous patients. These studies revealed that the Arctic mutation accelerates both A beta oligomerization and fibrillogenesis in vitro. In addition, A beta 40ARC was observed to affect both the morphology and the size distribution of A beta protofibrils. Electron microscopy examination of the protofibrils formed by A beta 40ARC revealed several morphologies, including: (1) relatively compact spherical particles roughly 4-5 nm in diameter; (2) annular pore-like protofibrils; (3) large spherical particles 18-25 nm in diameter; and (4) short filaments with chain-like morphology. Conversion of A beta 40ARC protofibrils to fibrils occurred more rapidly than protofibrils formed in mixed solutions of A beta 40WT/A beta 40ARC, suggesting that co-incubation of A beta 40ARC with A beta 40WT leads to kinetic stabilization of A beta 40ARC protofibrils. An increase in the ratio of A beta WT/A beta MUT(Arctic), therefore, may result in the accumulation of potential neurotoxic protofibrils and acceleration of disease progression in familial Alzheimer's disease mutation carriers.