Before revision: This region belongs to the N-terminal unstructured region ( 1-123 ) of prion proteins , the structure of which has proved hard to determine using NMR spectroscopy or X-ray crystallography due to the insoluble and noncrystalline nature of the amyloid fibril .
After revision: This region belongs to the N-terminal unstructured region ( 1-123 ) of prion proteins , the structure of which has proved hard to determine using NMR spectroscopy or X-ray crystallography due to the noncrystalline and insoluble nature of the amyloid fibril .