Biological Significance of Intrinsically Disordered Protein Structure

Structural biology comprises "Structured biology" based on folded structure and "Unstructured biology" based on unfolded structure. Principal of "Unstructured biology" is intrinsically disordered protein (IDP), in which the polypeptide chain is highly disordered under physiological conditions. The length of the disordered polypeptide may extend to several hundred residues or more. Further, in protein comprising multiple domains, long disordered polypeptides exist between domains, even if each domain has a regularly folded structure. Such polypeptide region is called intrinsically disordered region (IDR). Several IDPs and IDRs exist in living cells and play important biological roles in intracellular networks. Here, the biological significance of IDP and IDR from various viewpoints are described. Overall, this review aims to encourage further studies on "Unstructured biology" based on unfolded/disordered protein structure.