The problem, from what I understand as a dabbler in protein research, is that PrP binds into these large very very stable semi crystalline fibers, (I visualize them looking like thick extruded complicated pasta shapes, where the 2d crosssection is kinda the shape of the outline of a single PrP). It makes it really hard to learn about the structure, actually, because x-ray crystallography requires repeated crystalline structures, and these are more like 3d polymer threads that bunch up and make things hard to image (though there's some more modern imaging techniques that are making headway). It turns out that these are very very stable configurations unfortunately and have very few ways to attach anything, and that's the precise problem with building binders. Plus, even worse, it turns out PrP might even be biologically necessary for mammals and we don't want to usually get rid of it wholesale [https://bmcbiol.biomedcentral.com/articles/10.1186/s12915-01...]