The prion 2018 round tables (I): the structure of PrP(Sc)

Understanding the structure of PrP(Sc) is without doubt a sine qua non to understand not only PrP(Sc) propagation, but also critical features of that process such as the strain phenomenon and transmission barriers. While elucidation of the PrP(Sc) structure has been full of difficulties, we now have a large amount of structural information that allows us to begin to understand it. This commentary article summarizes a round table that took place within the Prion 2018 meeting held in Santiago de Compostela to discuss the state of the art in this matter. Two alternative models of PrP(Sc) exist: the PIRIBS and the 4-rung β-solenoid models. Both of them have relevant features. The 4-rung β-solenoid model agrees with experimental constraints of brain derived PrP(Sc) obtained from cryo-EM and X-ray fiber diffraction studies. Furthermore, it allows facile accommodation of the bulky glycans that decorate brain-derived PrP(Sc). On the other hand, the infectious PrP23-144 amyloid exhibits a PIRIBS architecture. Perhaps, both types of structure co-exist.