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Amyloid is formed through the polymerization of hundreds to thousands of monomeric peptides or proteins into long fibers. Amyloid formation involves a lag phase (also called nucleation phase), an exponential phase (also called growth phase) and a plateau phase (also called saturation phase), as shown in the figure.
Amyloid beta (Aβ, Abeta or beta-amyloid) denotes peptides of 36–43 amino acids that are the main component of the amyloid plaques found in the brains of people with Alzheimer's disease. [2] The peptides derive from the amyloid-beta precursor protein (APP), which is cleaved by beta secretase and gamma secretase to yield Aβ in a cholesterol ...
p3 peptide also known as amyloid β- peptide (Aβ) 17–40/42 is the peptide resulting from the α-and γ-secretase cleavage from the amyloid precursor protein ().It is known to be the major constituent of diffuse plaques observed in Alzheimer's disease (AD) brains and pre-amyloid plaques in people affected by Down syndrome.
APP is an integral membrane protein whose proteolysis generates beta amyloid ranging from 39- to 42- amino acid peptide. Although the biological function of APP are not known, it has been hypothesized that APP may play a role during neuroregeneration, and regulation of neural activity, connectivity, plasticity, and memory.
Amyloid beta is a short peptide that is an abnormal proteolytic byproduct of the transmembrane protein amyloid-beta precursor protein (APP), whose function is unclear but thought to be involved in neuronal development. [2] The presenilins are components of proteolytic complex involved in APP processing and degradation. [3] [4]
The normal function of Aβ is not certain, but plaques arise when the protein misfolds and begins to accumulate in the brain by a process of molecular templating ('seeding'). [36] Mathias Jucker and Lary Walker have likened this process to the formation and spread of prions in diseases known as spongiform encephalopathies or prion diseases.
Thus, alpha-secretase cleavage precludes amyloid beta formation and is considered to be part of the non-amyloidogenic pathway in APP processing. Alpha secretases are members of the ADAM ('a disintegrin and metalloprotease domain') family, which are expressed on the surfaces of cells and anchored in the cell membrane .
Some proteins that are disordered or helical as monomers, such as amyloid β (see amyloid plaque) can form β-sheet-rich oligomeric structures associated with pathological states. The amyloid β protein's oligomeric form is implicated as a cause of Alzheimer's. Its structure has yet to be determined in full, but recent data suggest that it may ...