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To date, 37 human proteins have been found to form amyloid in pathology and be associated with well-defined diseases. [2] The International Society of Amyloidosis classifies amyloid fibrils and their associated diseases based upon associated proteins (for example ATTR is the group of diseases and associated fibrils formed by TTR). [3]
Amyloid beta is commonly thought to be intrinsically unstructured, meaning that in solution it does not acquire a unique tertiary fold but rather populates a set of structures. As such, it cannot be crystallized and most structural knowledge on amyloid beta comes from NMR and molecular dynamics .
Amyloid-beta precursor protein (APP) is an integral membrane protein expressed in many tissues and concentrated in the synapses of neurons. It functions as a cell surface receptor [ 5 ] and has been implicated as a regulator of synapse formation , [ 6 ] neural plasticity , [ 7 ] antimicrobial activity, [ 8 ] and iron export . [ 9 ]
Misfolded proteins can form protein aggregates or amyloid fibrils, get degraded, or refold back to its native structure. In molecular biology, protein aggregation is a phenomenon in which intrinsically-disordered or mis-folded proteins aggregate (i.e., accumulate and clump together) either intra- or extracellularly.
Amyloid deposits in tissue can cause enlargement of structures. Twenty percent of people with AL amyloidosis have an enlarged tongue, that can lead to obstructive sleep apnea, difficulty swallowing, and altered taste. [11] Tongue enlargement does not occur in ATTR or AA amyloidosis. [10] Deposition of amyloid in the throat can cause hoarseness ...
The cytokines may induce neighboring cells to synthesize amyloid precursor protein. The proteases then possibly could cause the cleaving required to turn precursor molecules into the beta amyloid that characterizes the disease. Then, the oxygen species encourage the aggregation of beta amyloid in order to form plaques.
However, several aspects of amyloid biology are still under investigation. For example, recent evidence has suggested that amyloid plaque formation is linked to brain microvascular trauma. [49] [50] Other research implicates chronic inflammation of the brain and immune dysfunction of the nervous system. [51] [52]
Acute-phase serum amyloid A proteins (A-SAAs) are secreted during the acute phase of inflammation.These proteins have several roles, including the transport of cholesterol to the liver for secretion into the bile, the recruitment of immune cells to inflammatory sites, and the induction of enzymes that degrade extracellular matrix.