Résumé
'Major prion protein' (PrP) is encoded in the human body by the PRNP gene also known as CD230 (cluster of differentiation 230). Expression of the protein is most predominant in the nervous system but occurs in many other tissues throughout the body. The protein can exist in multiple isoforms: the normal PrPC form, and the protease-resistant form designated PrPRes such as the disease-causing PrPSc(scrapie) and an isoform located in mitochondria. The misfolded version PrPSc is associated with a variety of cognitive disorders and neurodegenerative diseases such as in animals: ovine scrapie, bovine spongiform encephalopathy (BSE, mad cow disease), feline spongiform encephalopathy, transmissible mink encephalopathy (TME), exotic ungulate encephalopathy, chronic wasting disease (CWD) which affects deer; and in humans: Creutzfeldt–Jakob disease (CJD), fatal familial insomnia (FFI), Gerstmann–Sträussler–Scheinker syndrome (GSS), kuru, and variant Creutzfeldt–Jakob disease (vCJD). Similarities exist between kuru, thought to be due to human ingestion of diseased individuals, and vCJD, thought to be due to human ingestion of BSE-tainted cattle products. The human PRNP gene is located on the short (p) arm of chromosome 20 between the end (terminus) of the arm and position 13, from base pair 4,615,068 to base pair 4,630,233. PrP is highly conserved through mammals, lending credence to application of conclusions from test animals such as mice. Comparison between primates is especially similar, ranging from 92.9-99.6% similarity in amino acid sequences. The human protein structure consists of a globular domain with three α-helices and a two-strand antiparallel β-sheet, an NH2-terminal tail, and a short COOH-terminal tail. A glycophosphatidylinositol (GPI) membrane anchor at the COOH-terminal tethers PrP to cell membranes, and this proves to be integral to the transmission of conformational change; secreted PrP lacking the anchor component is unaffected by the infectious isoform. The primary sequence of PrP is 253 amino acids long before post-translational modification.
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