Amyloid Fibril Nucleation In Reverse Micelles

The 40-residue amyloid beta protein (Abeta) is the unstructured cleavage product of a common membrane protein that is produced in large quantities, but normally cleared from the brain before it exerts any apparent toxicity. Under some conditions, however, it undergoes a conformational change and aggregates into fibrils. These fibrils then coalesce into amyloid plaques, which are the pathognomonic brain lesions of Alzheimer‘s disease. The plaques are centers of active oxidative stress and neuronal death, so the conditions under which fibrils form is of high interest. When Abeta is encapsulated in a reverse micelle, its infrared spectrum indicates that it spontaneously adopts a fibril-like structure, which is remarkable because only one Abeta strand is present in each reverse micelle. That observation suggests that some aspect of the reverse micelle environment such as crowding, dehydration, proximity to a membrane, or high ionic strength may induce Abeta to nucleate amyloid fibril formation. Therefore, an understanding of the factors that induce Abeta to adopt fibril-like structure in reverse micelles may reveal what causes amyloid fibrils to form in Alzheimer's disease. Molecular dynamics simulations of Abeta in reverse micelles have been performed to identify and understand these factors. Results indicate that Abeta side chains penetrate the reverse micelle surface, anchoring the peptide in the membrane. Other interactions between peptide and membrane stabilize intrachain hydrogen bond formation and secondary structure. These interactions may be important factors in the formation of amyloid fibrils and the pathogenesis of Alzheimer‘s disease.