Prions are a destructive family of proteins, due to a transformational (mis-folding) of a alpha helix to a beta sheet. The beta sheets only represent 3% of the proteins secondary structure (Fig. 1) This minor change in protein conformation is enough to turn a useful protein into a highly destructive stable force.

Figure 1. 56% helical (5 helices; 59 residues) 3% beta sheet (2 strands; 4 residues) of 3070 rabbit prion

Its amino acid sequence (95% match in sheep) as well as its 3-D structure ( 97% similarity to humans) is highly conserved through different species. What makes misfolding such a problem is its ability to perpetuate misfolding of the surrounding proteins. It has been found that rabbits have a helix capping motif the dramatically lowers the propensity of prion formation (Fig. 2)



Figure 2: Mouse vs Rabbit 3-D cartoon structure using Pymol

In conclusion prions have a highly conserved structure that is both minor yet destructive.