Comparison of the structures of amyloid beta protein in a non-polar medium (left) with alpha helices, and the conformation found in pathogenic amyloid plaques, with a beta sheet structure (right). Amyloid beta is a small protein found in the plaques in the brain of people with Alzheimer's disease. It is thought that the beta sheet form of the protein is the neurotoxic agent responsible for the symptoms of Alzheimer's disease. These are NMR solution structures.