The Unfolded Protein State Revisited

Abstract

Most studies on proteins have centered on the conformation and stability of the folded state. The unfolded state has essentially been neglected because of its reputation of being devoid of biological function, and not well-defined. Recently the importance of unfolded segments, as part of the secondary structure of globular proteins and their role in the performance of biological functions, has become apparent. We also are beginning to realize that there may be a surprising simplicity to what previously appeared to be a heterogeneous disorder. Thus the unfolded state can be characterized as having, in part, the same conformation as that adopted by a single polypeptide chain of the collagen molecule, termed the polyproline II (PPII) conformation. This PPII conformation has emerged as an important member in both the globular protein secondary structure and the unfolded state. Additionally, the important role of water in the stabilization of this conformation is crucial being the major determinant of it