G-quadruplexes within prion mRNA: the missing link in prion disease?

Abstract

Cellular ribonucleic acid (RNA) plays a crucial role in the initial conversion of cellular prion protein PrPC to infectious PrPSc or scrapie. The nature of this RNA remains elusive. Previously, RNA aptamers against PrPC have been isolated and found to form G-quadruplexes (G4s). PrPC binding to G4 RNAs destabilizes its structure and is thought to trigger its conversion to PrPSc. Here it is shown that PrP messenger RNA (mRNA) itself contains several G4 motifs, located in the octarepeat region. Investigation of the RNA structure in one of these repeats by circular dichroism, nuclear magnetic resonance and ultraviolet melting studies shows evidence of G4 formation. In vitro translation of full-length PrP mRNA, naturally harboring five consecutive G4 motifs, was specifically affected by G4-binding ligands, lending support to G4 formation in PrP mRNA. A possible role of PrP binding to its own mRNA and the role of anti-prion drugs, many of which are G4-binding ligands, in prion disease are discussed.

The “Jekyll and Hyde” Actions of Nucleic Acids on the Prion-like Aggregation of Proteins

“…Recent studies have shown that both DNA and RNA quadruplex structures bind PrP with a high affinity (44,46) and can modify the PrP conformation. It was shown that PrP can bind its own mRNA, which contains G4 motifs, causing it to form a quadruplex structure under particular conditions (47). It is becoming more and more obvious that PrP binds to structured nucleic acids, and both the nucleic acid and the protein undergo structural changes when this interaction occurs (29,43,44,48,49).…”

Characterization of G‐Quadruplex/Hairpin Transitions of RNAs by 19F NMR Spectroscopy

“…One important example of such bistable stretches may be found in the mRNA of human cellular prion protein (PrP). Recent studies suggest that prion diseases (e.g., Creutzfeldt–Jakob disease) may, in fact, originate from the partial Qd conformers within PrP mRNA, which, under certain circumstances, may induce the formation of misfolded PrP . Due to the dynamic equilibrium and aggregation, characterization of the secondary structural species (G‐quadruplex/hairpin/single‐strand, Qd/Hp/Ss) and the determination of their molar fractions upon conformational transitions is complex.…”

“…Due to the dynamic equilibrium and aggregation, characterization of the secondary structural species (G‐quadruplex/hairpin/single‐strand, Qd/Hp/Ss) and the determination of their molar fractions upon conformational transitions is complex. 1 H NMR, UV, and CD spectroscopic analyses of a bistable Qd/Hp RNA model (exhibiting an artificial fusion of Qd‐ and Hp‐forming sequences) and of Qd/Hp transitions within PrP mRNA have recently been reported.…”

“…In the present study, phosphoramidite building blocks of 2′‐ O ‐[(4‐CF 3 ‐triazol‐1‐yl)methyl]cytidine ( 10 ), ‐adenosine ( 11 ), and ‐guanosine ( 12 ) have been synthesized and incorporated into potential bistable Qd/Hp RNA models, and the applicability of the 2′‐ O ‐[(4‐CF 3 ‐triazol‐1‐yl)methyl reporter group for 19 F NMR spectroscopic detection of plausible Qd/Hp transitions has been evaluated. The RNAs investigated were 19 F‐labeled analogues of previously studied bistable Qd/Hp RNA models: an artificial fusion of Hp‐ and Qd‐forming sequences ( ORN 2 and ORN 3 , Table and Scheme ; the hairpin derived from mouse mammary tumor virus and the Qd‐forming sequence from human N‐RAS messenger RNA) and two G‐rich regions of prion mRNA ( ORN 8 and ORN 10 , Table and Scheme ). The artificial fusion sequence ( ORN 2 and ORN 3 ), with well‐documented background data, served as an RNA model that could be used to prove the versatility of 19 F NMR spectroscopic detection, whereas the possible additional information offered by prion RNA models ( ORN 8 and ORN 10 ) is of the utmost importance for prion disease studies .…”

Structure and target interaction of a G-quadruplex RNA-aptamer

“…17 One such characteristic connected with GQ affinity in some proteins is the presence of the stabilizing Arg-Gly-Gly (RGG) repeats as found for example in fragile X mental retardation protein, 18 nucleolin (a multifunctional heterogeneous nuclear ribonucleoprotein (hnRNP) belonging to the family of RNA binding proteins) 19 or engineered proteins. 20 GQ forming aptamers include for example nucleolinspecific DNA aptamer AS1411, 21 thrombin binding aptamer, 22 HIV1 aptamer T30177, 23 aptamers for prion proteins [24][25][26] or fluorophore binding aptamer spinach. 27 Another example is given by aptamer AIR-3 which has specificity for human interleukin-6 receptor (hIL-6R).…”