Β-amyloid

β-amyloid (also known as Amyloid beta, Aβ or Abeta) is a peptide of 36–43 amino acids that is crucially involved in Alzheimer's disease as the main component of the amyloid plaques found in the brains of Alzheimer patients. The peptides derive from the amyloid precursor protein (APP), which is cleaved by beta secretase and gamma secretase to yield Aβ. Aβ molecules can aggregate to form flexible soluble oligomers which may exist in several forms. It is now believed that certain misfolded oligomers can induce other Aβ molecules to also take the misfolded oligomeric form, leading to a chain reaction akin to a prion infection. The oligomers are toxic to nerve cells. The other protein implicated in Alzheimer's disease, tau protein, also forms such prion-like misfolded oligomers, and there is some evidence that misfolded Aβ can induce tau to misfold.

Structure and function

Aβ is the main component of deposits found in the brains of patients with Alzheimer's disease. These deposits, called senile plaques, are composed of a tangle of regularly ordered fibrillar aggregates called amyloid fibers, a protein fold shared by other peptides such as the prions associated with protein misfolding diseases.

Clinical significance

The "amyloid hypothesis", that the plaques are responsible for the pathology of Alzheimer's disease, is accepted by the majority of researchers but is by no means conclusively established. It is generally believed that Aβ oligomers are the most toxic. A number of genetic, cell biology, biochemical and animal model studies support the concept that Aβ plays a central role in the development of Alzheimer’s disease pathology.

See also

• Alzheimer's disease
• Amyloid precursor protein
• Beta secretase
• Gamma secretase
• Prion