Diversity of hydrodynamic radii of intrinsically disordered proteins

Intrinsically disordered proteins (IDPs) form an important class of biomolecules regulating biological processes in higher organisms. The lack of a fixed spatial structure facilitates them to perform their regulatory functions. Due to the possibility of large conformational changes of IDPs, the cellular milieu can also control productivity of biochemical reactions. From the biophysical point of view, IDPs are biopolymers with a broad configuration state space. The conformation of such a biopolymer depends on non-covalent interactions of its amino acid side chain groups at given temperature and chemical conditions. Thus, the hydrodynamic radius (Rh) of an IDP of a given polymer length (N) is a sequence- and environment-dependent variable. We have reviewed the literature values of hydrodynamic radii of IDPs determined experimentally by SEC, AUC, PFG NMR, DLS, and FCS, and complement them with our FCS results obtained for a series of protein fragments involved in regulation of human gene expression. The data collected herein show that the values of hydrodynamic radii of intrinsically disordered proteins can span the full space between the folded globular and denatured proteins in the Rh(N) diagram.