Structure of the β2‐α2 loop and interspecies prion transmission

Abstract

Prions are misfolded, aggregated conformers of the prion protein that can be transmitted between species. The precise determinants of interspecies transmission remain unclear, although structural similarity between the infectious prion and host prion protein is required for efficient conversion to the misfolded conformer. The β2-α2 loop region of endogenous prion protein, PrP(C), has been implicated in barriers to prion transmission. We recently discovered that conversion was efficient when incoming and host prion proteins had similar β2-α2 loop structures; however, the roles of primary vs. secondary structural homology could not be distinguished. Here we uncouple the effect of primary and secondary structural homology of the β2-α2 loop on prion conversion. We inoculated prions from animals having a disordered or an ordered β2-α2 loop into mice having a disordered loop or an ordered loop due to a single residue substitution (D167S). We found that prion conversion was driven by a homologous primary structure and occurred independently of a homologous secondary structure. Similarly, cell-free conversion using PrP(C) from mice with disordered or ordered loops and prions from 5 species correlated with primary but not secondary structural homology of the loop. Thus, our findings support a model in which efficient interspecies prion conversion is determined by small stretches of the primary sequence rather than the secondary structure of PrP.

Cross-species transmission of CWD prions

“…48,52,53 Instead, the amino acid sequence of the b2-a2 loop has an important role in promoting CWD conversion of PrP C from other species. However, as the ferret and the squirrel monkey are highly susceptible to CWD infection, and neither has a b2-a2 loop that matches elk, it is clear that other PrP segments also interact during CWD conversion.…”

“…43 The resulting Tg(MoPrP S170N,N174T ) mice were highly susceptible to CWD infection compared to mice expressing wild type mouse PrP C . 47 Further studies utilizing mice with a well-defined loop due to a different substitution, D167S, showed that the loop conformation had no effect on CWD susceptibility, 48 as the mice had identical barriers as WT mice. Taken together, these results suggest that the 165-175 sequence similarity between cervid and host PrP, and not the secondary structure, governs CWD susceptibility.…”

Structural plasticity of the cellular prion protein and implications in health and disease

“…Despite extensive investigations, the physiological function of PrP C in healthy organisms as well as the mechanistic aspects of its pathophysiological role remain elusive (4)(5)(6)(7)(8)(9). Although the PrP Sc form found in diseased tissue has been intensively studied, other approaches underline the importance of PrP C as a potential target for TSE prevention and medical intervention after outbreak of the disease (10)(11)(12), with a special focus on rigid-loop cellular prion proteins (RL-PrP C s) (11,(13)(14)(15), which are investigated in this paper.…”

“…Despite extensive investigations, the physiological function of PrP C in healthy organisms as well as the mechanistic aspects of its pathophysiological role remain elusive (4-9). Although the PrP Sc form found in diseased tissue has been intensively studied, other approaches underline the importance of PrP C as a potential target for TSE prevention and medical intervention after outbreak of the disease (10-12), with a special focus on rigid-loop cellular prion proteins (RL-PrP C s) (11,(13)(14)(15), which are investigated in this paper.A common PrP C fold for a globular domain formed by the polypeptide segment of residues 125-228 in mouse PrP (mPrP) [see Schätzl et al (16) for the numeration in different species], with three α-helices and a short two-stranded antiparallel β-sheet, has been observed for the cellular prion proteins of all mammalian species studied so far (17-27). For WT PrP of most species, parts of the backbone amide group NMR signals of residues in a loop between a β-strand, β2, and a helix, α2, are not observable in NMR spectra recorded with aqueous solutions at pH 4.5 and 20°C at a 1 H resonance frequency of 500 MHz (or higher) because of line broadening by conformational exchange; therefore, the β2-α2 loop in these PrP C s is poorly defined in NMR structures determined under these conditions.…”

Caprine PrP variants harboring Asp-146, His-154 and Gln-211 alleles display reduced convertibility upon interaction with pathogenic murine prion protein in scrapie infected cells

“…45 The significance of the H2S2 loop region in interspecies prion transmission has been highlighted by another study, which points out the importance of primary sequence rather than structural similarities. 46 Furthermore, correlation of multiple amino acid residues with the murine-rabbit 'species barrier', suggests that primary sequence differences between interacting PrP isoforms may be associated with conversionincompatible structures. 47 Studies on heterologous PrP interactions revealed altered molecular associations 42,48 and lower conversion efficiencies.…”