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Title: The architecture of PrPSc: Threading secondary structure elements into the 4-rung ß-solenoid scaffold

Author
item SEVILLANO, ALEJANDRO - University Of Santiago De Compostela
item CHAKRABORTY, SANDIPAN - Indian Statistical Institute
item VAZQUEZ-FERNANDEZ, ESTER - University Of Alberta
item Silva, Christopher - Chris
item REQUENA, JESUS - University Of Santiago De Compostela

Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: 3/15/2017
Publication Date: 5/25/2017
Citation: Sevillano, A.M., Chakraborty, S., Vazquez-Fernandez, E., Silva, C.J., Requena, J.R. 2017. The architecture of PrPSc: Threading secondary structure elements into the 4-rung ß-solenoid scaffold. Meeting Abstract. Prion 2017: Poster 221..

Interpretive Summary:

Technical Abstract: Aims: We propose to exploit the wealth of theoretical and experimental constraints to develop a structure of the infectious prion (hamster PrP27-30). Recent cryo-EM based evidence has determined that PrPSc is a 4-rung ß-solenoid (Vázquez-Fernández et al. 2016, PLoS Pathog. 12(9): e1005835). This evidence is in agreement with earlier fiber X-ray diffraction studies. Therefore, PrPSc consists of a number of short ß-strands connected by short loops and turns. Unfortunately, the resolution of the analytical techniques used to study PrPSc structure is not adequate to identify these elements of secondary structure. Methods: We used available structural constraints to develop our model. (1) The newly reinterpreted PrP27-30 FTIR spectra of PrP27-30 strongly suggest that approximately 50% of PrP27-30 sequence is part of a ß-strand while the other approximately 50% is random coil without ß-helical structure (Requena & Wille, 2014, Prion 8:1-7). (2) The Cys179-Cys214 disulphide bond dictates that Cys179 and Cys214 must be in different (successive) rungs. Furthermore, they are likely to be in loop/turn regions, as is found in the intermolecular disulfide bonds of insulin amyloid subunits. (3) Furthermore, the structural constraints of the five Pro residues mean that they must be in loops or at the edge of ß-strands. (4) Asp180 and Asp196 residues can be electively glycosylated, and so they are likely to be positioned in random coil/turn locations, to allow external protrusion of bulky glycan chains.(5) The minor proteinase K (PK)-resistant fragments consistently found in strains and types of PrPSc isolates after limited proteolysis of PrPSc can be used to identify the boundaries between loops and ß-strands. (6) Many of these PK cleavage sites are located near P residues, which is consistent with our positioning of the Pro residues. Results: When combining these empirical constraints with the dimensions of PrPSc protofilaments provided by reconstruction of cryo-EM images, we have constructed a threading model of PrPSc. The resulting structural model facilitates molecular interrogation of and predictions about key issues in PrPSc prion biology, such as strains and transmission barriers. Conclusions: We have generated a structural model of hamster PrPSc (PrP27-30). This structural model accommodates the recently acquired experimental structural constraints. Our model represents a starting point which can be further refined by adding new experimental constraints and employing advanced molecular modeling approaches.