Amyloid-beta

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 result 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

Aβ is the main component of deposits found in the brains of Alzheimer's patients. These deposits 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.

Function

Despite the fact that Aβ is ubiquitously expressed in all organ systems, its physiological function is unknown. Part of the reason for this lack of understanding is that Aβ is not essential for life, as mice lacking the gene for APP (and thus Aβ) develop normally and are fertile with no apparent deficits in health or longevity.

Role in disease

Aβ is the main constituent of brain plaques associated with Alzheimer's Disease. The most toxic form of Aβ may be oligomers. It is not clear how Aβ accumulates in the brain to levels toxic to neurons.

See also

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

Amyloid-beta Resources
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