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Proteopathy
In medicine, proteopathy (Proteo- (protein ); -pathy (disease ); proteopathies ''pl''.; proteopathic ''adj''.) refers to a class of diseases in which certain proteins become structurally abnormal, and thereby disrupt the function of cells, tissues and organs of the body. Often the proteins fail to fold into their normal configuration; in this misfolded state, the proteins can become toxic in some way (a gain of toxic function) or they can lose their normal function. The proteopathies (also known as proteinopathies, protein conformational disorders, or protein misfolding diseases) include such diseases as Creutzfeldt–Jakob disease, Alzheimer's disease, Parkinson's disease, prion disease, amyloidosis, and a wide range of other disorders (see List of Proteopathies).〔
The concept of proteopathy can trace its origins to the mid-19th century, when, in 1854, Rudolf Virchow coined the term amyloid ("starch-like") to describe a substance in cerebral corpora amylacea that exhibited a chemical reaction resembling that of cellulose. In 1859, Friedreich and Kekulé demonstrated that, rather than consisting of cellulose, "amyloid" actually is rich in protein. Subsequent research has shown that many different proteins can form amyloid, and that all amyloids have in common birefringence in cross-polarized light after staining with the dye Congo Red, as well as a fibrillar ultrastructure when viewed with an electron microscope.〔 However, some proteinaceous lesions lack birefringence and contain few or no classical amyloid fibrils, such as the diffuse deposits of Aβ protein in the brains of Alzheimer patients. Furthermore, evidence has emerged that small, non-fibrillar protein aggregates known as oligomers are toxic to the cells of an affected organ, and that amyloidogenic proteins in their fibrillar form may be relatively benign.
==Pathophysiology==
In most, if not all proteopathies, a change in 3-dimensional folding (conformation) increases the tendency of a specific protein to bind to itself.〔 In this aggregated form, the protein is resistant to clearance and can interfere with the normal capacity of the affected organs. In some cases, misfolding of the protein results in a loss of its usual function. For example, cystic fibrosis is caused by a defective cystic fibrosis transmembrane conductance regulator (CFTR) protein,〔 and in amyotrophic lateral sclerosis / frontotemporal lobar degeneration (FTLD), certain gene-regulating proteins inappropriately aggregate in the cytoplasm, and thus are unable to perform their normal tasks within the nucleus. Because proteins share a common structural feature known as the polypeptide backbone, all proteins have the potential to misfold under some circumstances. However, only a relatively small number of proteins are linked to proteopathic disorders, possibly due to structural idiosyncrasies of the vulnerable proteins. For example, proteins that are relatively unstable as monomers (that is, as single, unbound protein molecules) are more likely to misfold into an abnormal conformation.〔〔 In nearly all instances, the disease-causing molecular configuration involves an increase in beta-sheet secondary structure of the protein.〔〔 The abnormal proteins in some proteopathies have been shown to fold into multiple 3-dimensional shapes; these variant, proteinaceous structures are defined by their different pathogenic, biochemical, and conformational properties. They have been most thoroughly studied with regard to prion disease, and are referred to as protein strains.
The likelihood that proteopathy will develop is increased by certain risk factors that promote the self-assembly of a protein. These include destabilizing changes in the primary amino acid sequence of the protein, post-translational modifications (such as hyperphosphorylation), changes in temperature or pH, an increase in production of a protein, or a decrease in its clearance.〔〔〔 Advancing age is a strong risk factor,〔 as is traumatic brain injury. In the aging brain, multiple proteopathies can overlap. For example, in addition to tauopathy and Aβ-amyloidosis (which coexist as key pathologic features of Alzheimer's disease), many Alzheimer patients have concomitant synucleinopathy (Lewy bodies) in the brain.
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』
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