The Effect of Octapeptide Repeats on Prion Folding and Misfolding

Abstract

Misfolding of prion protein (PrP) into amyloid aggregates is the central feature of prion diseases. PrP has an amyloidogenic C-terminal domain with three α-helices and a flexible tail in the N-terminal domain in which multiple octapeptide repeats are present in most mammals. The role of the octapeptides in prion diseases has previously been underestimated because the octapeptides are not located in the amyloidogenic domain. Correlation between the number of octapeptide repeats and age of onset suggests the critical role of octapeptide repeats in prion diseases. In this study, we have investigated four PrP variants without any octapeptides and with 1, 5 and 8 octapeptide repeats. From the comparison of the protein structure and the thermal stability of these proteins, as well as the characterization of amyloids converted from these PrP variants, we found that octapeptide repeats affect both folding and misfolding of PrP creating amyloid fibrils with distinct structures. Deletion of octapeptides forms fewer twisted fibrils and weakens the cytotoxicity. Insertion of octapeptides enhances the formation of typical silk-like fibrils but it does not increase the cytotoxicity. There might be some threshold effect and increasing the number of peptides beyond a certain limit has no further effect on the cell viability, though the reasons are unclear at this stage. Overall, the results of this study elucidate the molecular mechanism of octapeptides at the onset of prion diseases.

DNA Aptamer Binding Octapeptide Repeat Region of Cellular Prion Protein

“…32,33 Yu et al constructed mouse prion proteins without and with one or seven octapeptide repeats and found that deletion or insertion of the prion Nterminal octapeptide repeats increased the structural proportion of the C-terminal α helix, and prion protein containing 7 octapeptide repeat units converted significantly more protofibrils and provided partial protease resistance. 34 To verify whether HA5-68 binds to the octapeptide repeat region of PrP C , the whole octapeptide repeat region, peptide OR-41 (residues 51-91) was synthesized and used to compete with the binding between HA5-68 and PC-3 cells. As shown in Figure 3A, 2 μM peptide OR-41 greatly reduced the level of binding of 20 nM HA5-68 to PC-3 cells by approximately 97.96%, but the control peptide (Pep-Ctr) at the same concentration did not affect the binding of HA5-68 to PC-3 cells.…”

“…Creutzfeldt–Jakob disease (CJD) is the most common form of prion disease in humans. More and more literature studies have documented that 1 to 9 (except 3) additional repeats occur in the octapeptide repeat region, depending on the type of CJD. , Yu et al constructed mouse prion proteins without and with one or seven octapeptide repeats and found that deletion or insertion of the prion N-terminal octapeptide repeats increased the structural proportion of the C-terminal α helix, and prion protein containing 7 octapeptide repeat units converted significantly more protofibrils and provided partial protease resistance …”

SORL1 gene mutation and octapeptide repeat insertion in PRNP gene in a case presenting with rapidly progressive dementia and cerebral amyloid angiopathy

“…Even in these cases, neuroimaging did not show typical features of CAA. To date, there is no clear evidence of association between a single OPRI and CAA, but a recent study showed that insertion of octapeptides, even if not located in the amyloidogenic domain, may weaken the α‐helical PrP structure, promoting the formation of prion amyloid fibrils [39].…”

Protein Aggregation Landscape in Neurodegenerative Diseases: Clinical Relevance and Future Applications

“…PrP-C is a glycosyl phosphoinositol anchored membrane glycoprotein. Its N-terminal moiety presents a variable number of octapeptide repeats enriched in Glycine residues [104][105][106] forming the LCD of PrP. Traditionally, low complexity regions displaying infectivity have been often referred to as prion-like domains [1,2,5,6,8,9,73].…”

“…However, it required a longer incubation time and resulted in a lower PrP titer compared to the overexpression of the full-length version. Insertion of multiple octapeptide repeats increases the flexibility of the structure, weakening the α-helix in the C-terminal domain, thus promoting aggregation [105,109]. This evidence suggests that, whilst the N-terminal LCD of PrP-C is not essential for prion replication, it does have an effect on the rate of prion accumulation.…”