One of the textbook concepts in molecular biology is that proteins fold up spontaneously to form the most energetically stable three-dimensional structures. These folded proteins are presumed structurally rigid, which is important for their unique functionality, e.g. as enzymes. There are indications, however, mostly coming from NMR studies, that many important proteins exist in disordered form. A news feature in the latest issue of Nature discusses implications of this potentially far-reaching finding. Among cited examples of intrinsically disordered proteins is the NMR study on Sic1 protein by Julie Forman-Kay and her group at the University of Toronto/SickKids.
T. Chouard "Structural biology: Breaking the protein rules," Nature 471 (2011) 151-153. http://www.nature.com/news/2011/110309/full/471151a.html