Some proteins are intrinsically unstructured to support their functions.
  1. ~10% of proteins are predicted to be fully disordered.

  2. ~40% of eukaryotic proteins have at least one long (>50 residues) disordered region.
      Missing ends and loops in crystal structures may often be intrinsically unstructured. Recent literature ...

by Eric Martz, University of Massachusetts, October 2004 for ProteinExplorer.Org.