The interplay between structure and function in intrinsically unstructured proteins

Intrinsically unstructured proteins (IUPs) are common in various proteomes and occupy a unique structural and functional niche in which function is directly linked to structural disorder. The evidence that these proteins exist without a well-defined folded structure in vitro is compelling, and justifies considering them a separate class within the protein world. In this paper, novel advances in the rapidly advancing field of IUPs are reviewed, with the major attention directed to the evidence of their unfolded character in vivo, the interplay of their residual structure and their various functional modes and the functional benefits their malleable structural state provides. Via all these details, it is demonstrated that in only a couple of years after its conception, the idea of protein disorder has already come of age and transformed our basic concepts of protein structure and function. (c) 2005 Federation of European Biochemical Societies. Published by Elsevier B.V. All rights reserved.