Sabzehei, S.; Erana, H.; Diaz-Arias, I.; Cacheiro, R.; Guerra, A.; Alvarez-Cardama, S. M.; de Leon-Vega, Y.; Rezaei, H.; Castilla, J.; Sanchez-Pedregal, V.; Requena, J. R.; Martin-Pastor, M.

The elucidation of the atomistic structure of PrPSc has, disappointingly, not revealed the mechanism underlying prion propagation. This is because PrPSc has been shown to be a standard amyloid, and as such, it can only template a polypeptide chain that is unfolded. Therefore, while PrPSc can easily template the disordered ~90-120 domain of an incoming PrPC molecule, it does not have any obvious capacity to template its ~121-231 folded domain (FD). The FD needs to accommodate into the ~121-230 PrPSc surface, an inert "Procrustean bed". We have recently proposed that unfolding of the FD is a prerequisite for its conversion to the PrPSc conformation and using experimental and computational methods identified the likely early events of such process using bank vole (BV)PrP(90-231) as our working model. We concluded that a key early event is the destabilization of the short {beta}1-{beta}2 assembly, and that the segment contiguous to the disordered tail, ~121-140, encompassing {beta}1 and its adjacent coils, is the most likely region to unfold first. In the present study we applied the same methodology to the disease-related PrP mutant E200K. E200K is the most prevalent mutation leading to familial prion disease in humans, yet the stability of its FD is only marginally lower compared to that of the protein with the wild type (wt) sequence. We, therefore, aimed at assessing whether the early unfolding events of BVPrPC(E200K) are similar or different to those of wtBVPrPC and whether such early unfolding route might provide insight into the extreme capacity of PrPC(E200K) to spontaneously generate PrPSc. It should be noted that generation and propagation of PrPSc are distinct phenomena, even though both are mechanistically related and dependent on conformational changes in PrPC. Our data show that early unfolding events of BVPrPC(E200K) are essentially similar to those of wt BVPrPC. However, interesting nuances exist.