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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 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 ...
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.
The hypothesis that tau is the primary causative factor has long been grounded in the observation that deposition of amyloid plaques does not correlate well with neuron loss. [31] A mechanism for neurotoxicity has been proposed based on the loss of microtubule-stabilizing tau protein that leads to the degradation of the cytoskeleton. [32]
However, neuronal cell bodies contain less APP as a function of their proximity to amyloid plaques. [37] The data indicate that this deficit in APP results from a decline in production rather than an increase in catalysis. Loss of a neuron's APP may affect physiological deficits that contribute to dementia.
Amyloid plaques naturally occur in the aging brains of nonhuman species ranging from birds to great apes. [4] In nonhuman primates, which are the closest biological relatives of humans, plaques have been found in all species examined thus far. [ 47 ]
According to the prevailing amyloid hypothesis of Alzheimer's disease, the aggregation of amyloid-beta (a peptide normally produced in and cleared from the healthy young brain) into extracellular plaques drives the neuronal loss and brain atrophy that is the hallmark of Alzheimer's dementia.