A peptide is a small molecule in which amino acids, the building blocks of proteins, are held together by strong chemical bonds. Proteins can often be fragmented into peptides. A beta-amyloid peptide is a fragment derived from a large normal common protein, which, in the disease, is fragmented in an abnormal fashion. The beta-amyloid peptides found in Alzheimer's victims' brains are clipped off a larger normal protein called APP, which is found throughout the body. Normally, these beta-amyloid peptides are broken down to very small harmless fragments.
Nobody knows why they accumulate in the disease.
They become toxic with time. These fragments accumulate into abnormal fibers in the cortex to form the characteristic senile plaques, which look very distinctive under the microscope. In Alzheimer's disease, these aggregates of peptides can cause some neurons to get an influx of external calcium that is too large for the cell to pump out or isolate. The beta-amyloid peptide appears to open a channel into the neuron that allows calcium to enter it, making it malfunction and die. Although the decoys have yet to be evaluated for possible side effects, the researchers say that these could potentially be developed as therapeutic agents to reduce or delay the death of neurons that causes Alzheimer's.