Insoluble protein aggregate with a fibrillar morphology
For other uses, see Amyloid (disambiguation).
Micrograph showing amyloid deposits (pink) in small bowel. Duodenum with amyloid deposition in lamina propria. Amyloid shows up as homogeneous pink material in lamina propria and around blood vessels. 20× magnification.
Amyloids are aggregates of proteins characterised by a fibrillar morphology of typically 7–13 nm in diameter, a β-sheet secondary structure (known as cross-β) and ability to be stained by particular dyes, such as Congo red.[1] In the human body, amyloids have been linked to the development of various diseases.[2] Pathogenic amyloids form when previously healthy proteins lose their normal structure and physiological functions (misfolding) and form fibrous deposits within and around cells. These protein misfolding and deposition processes disrupt the healthy function of tissues and organs.
Such amyloids have been associated with (but not necessarily as the cause of) more than 50[2][3] human diseases, known as amyloidosis, and may play a role in some neurodegenerative diseases.[2][4] Some of these diseases are mainly sporadic and only a few cases are familial. Others are only familial. Some result from medical treatment. Prions are an infectious form of amyloids that can act as a template to convert other non-infectious forms.[5] Amyloids may also have normal biological functions; for example, in the formation of fimbriae in some genera of bacteria, transmission of epigenetic traits in fungi, as well as pigment deposition and hormone release in humans.[6]
Amyloids have been known to arise from many different proteins.[2][7] These polypeptide chains generally form β-sheet structures that aggregate into long fibers; however, identical polypeptides can fold into multiple distinct amyloid conformations.[8] The diversity of the conformations may have led to different forms of the prion diseases.[6]
An unusual secondary structure named α sheet has been proposed as the toxic constituent of amyloid precursor proteins,[9] but this idea is not widely accepted at present.
Amyloid of HET-s(218-289) prion pentamer, Podospora anserina (PDB: 2rnm)
^Sunde M, Serpell LC, Bartlam M, Fraser PE, Pepys MB, Blake CC (October 1997). "Common core structure of amyloid fibrils by synchrotron X-ray diffraction". Journal of Molecular Biology. 273 (3): 729–39. doi:10.1006/jmbi.1997.1348. PMID 9356260. S2CID 19394482.
^ abcdChiti F, Dobson CM (June 2017). "Protein Misfolding, Amyloid Formation, and Human Disease: A Summary of Progress Over the Last Decade". Annual Review of Biochemistry. 86: 27–68. doi:10.1146/annurev-biochem-061516-045115. hdl:2158/1117236. PMID 28498720.
^Benson MD, Buxbaum JN, Eisenberg DS, Merlini G, Saraiva MJ, Sekijima Y, et al. (December 2018). "Amyloid nomenclature 2018: recommendations by the International Society of Amyloidosis (ISA) nomenclature committee". Amyloid. 25 (4): 215–219. doi:10.1080/13506129.2018.1549825. hdl:1805/20251. PMID 30614283.
^Pulawski W, Ghoshdastider U, Andrisano V, Filipek S (April 2012). "Ubiquitous amyloids". Applied Biochemistry and Biotechnology. 166 (7): 1626–43. doi:10.1007/s12010-012-9549-3. PMC 3324686. PMID 22350870.
^Soto C, Estrada L, Castilla J (March 2006). "Amyloids, prions and the inherent infectious nature of misfolded protein aggregates". Trends in Biochemical Sciences. 31 (3): 150–5. doi:10.1016/j.tibs.2006.01.002. PMID 16473510.
^Ramirez-Alvarado M, Merkel JS, Regan L (August 2000). "A systematic exploration of the influence of the protein stability on amyloid fibril formation in vitro". Proceedings of the National Academy of Sciences of the United States of America. 97 (16): 8979–84. Bibcode:2000PNAS...97.8979R. doi:10.1073/pnas.150091797. PMC 16807. PMID 10908649.
^Cite error: The named reference pm11076514 was invoked but never defined (see the help page).
^Armen RS, Demarco ML, Alonso DO, Daggett V (2004). "Pauling and Coreys α-pleated sheet structure may define the prefibrillar amyloidogenic intermediate in amyloid disease". Proceedings of the National Academy of Sciences of the United States of America. 101 (1): 11622–11627. Bibcode:2004PNAS..10111622A. doi:10.1073/pnas.0401781101. PMC 511030. PMID 15280548.
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