The third shows a proposed binding site for protein X and hypothetical rogue prion in beta sheet conformatioon. Gln168, Gln172, Thr215, and Gln219 form part of the site of protein X binding. These side chains are on the surface of helix 3, forming a discontinuous epitope with residues 167 and 171 in an adjacent loop. These images show hamster and mouse prion proteins. The mouse structure is refined but shorter in length than the hamster.
Some problems remain .
Hamster maintains a striking positive face first observed in mouse. Met 129, a modulating locus in humans, is seen to bind tightly with Tyr 163 in the VYYR -YMLG beta sheet. The odd M109F substitution results in hudrophobic phenylalanine inappropriately on the exterior of the molecule in place of threonine, threading from hamster. The T189V substitution in helix 3 of long incubation mouse is again a hydrophobic residue, valine, inappropriately on the exterior of the molecule inplace of a polar residue. F198S is another CJD-causing mutation in this region.