Structure
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-stranded antiparallel β-sheet, an NH2-terminal tail, and a short COOH-terminal tail. A glycosylphosphatidylinositol (GPI) membrane anchor at the COOH-terminal tethers PrP to cell membranes, and this proves to be integral to the transmission of conformation change; secreted PrP lacking the anchor component is unaffected by the infectious isoform.
The primary sequence of PrP is 253 amino acids long before posttranslational modification. Signal sequences in the amino- and carboxy- terminal ends are removed posttranslationally resulting in a mature length of 208. For human and Syrian hamster PrP, two glycosylated sites exist on helices 2 and 3 at Asn181 and Asn197. Murine PrP has glycosylation sites as Asn180 and Asn196. A disulfide bond exists between Cys179 of the second helix and Cys214 of the third helix (human PrPC numbering).
PrP messenger RNA contains a pseudoknot structure (prion pseudoknot) which is thought to be involved in regulation of PrP protein translation.
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