Abstract Two alternative architectures have been proposed for PrP Sc , the most notorious prion: a parallel in register β stack (PIRIBS) and a 4-rung β-solenoid (4RβS). We challenged these two models by measuring intermolecular 13 C- 13 C dipole-dipole couplings of 13 CO-labelled Phe residues in a fully infectious sample of recombinant bank vole PrP Sc (recBVPrP Sc ) using a PITHIRDS-CT solid state NMR (ssNMR) experiment. To our surprise, data strongly support a PIRIBS architecture. However, the mean distance measured (∼6.5 Å) suggests that a minimum of two of the three Phe residues are not perfectly stacked at the canonical ∼5 Å cross-β distance. Additional ssNMR experiments show some local conformational variability of the Phe residues within limits of a relatively high rigidity. The most parsimonious interpretation of our data is that recBVPrP Sc is arranged as a PIRIBS, although additional conformers with alternative architectures cannot be excluded, including a mixture of PIRIBS and 4RβS. Author summary PrP Sc is the most notorious prion. It is an infectious protein that cuases fatal neurodegenerative diseases in humans and animals. PrP Sc is the aberrant version of a brain protein, PrP C . PrP Sc and PrP C have the same prinary structure, but different secondary, tertiaty and quaternary structures. PrP Sc is capable of templating PrP C to convert to the PrP Sc conformation, which is the basis of its capacity to propagate. Two plausible structural models of PrP Sc have been proposed, the four-rung β-solenoid (4RβS) and the parallel in-register β stack (PIRIBS) model. In both cases the driving force of the templating mechanism consists of “sticky” surface β-strands; however, in the PIRIBS model all the β-strands that conform a PrP Sc monomer lie flat on a surface whereas in the 4RβS model they wind in a corkscrew fashion. Here, we analyzed fully infectious recombinant PrP Sc using a solid state NMR technique, PITHIRDS, that allows probing distances between specific labelled amino acid residues. To our surprise (as we have defended the 4RβS model in the past), results clearly show the presence of a PIRIBS structure in our sample.

Solid state NMR reveals a parallel in register architecture for an infectious recombinant prion