The C-terminal domain of measles virus nucleoprotein belongs to the class of intrinsically disordered proteins that fold upon binding to their physiological partner

The nucleoprotein of measles virus consists of an N-terminal domain, N-CORE (aa 1-400), resistant to proteolysis, and a C-terminal domain, N-TAIL (aa 401-525), hypersensitive to proteolysis and not visible by electron microscopy. Using two complementary computational approaches, we predict that N-TAIL belongs to the class of natively unfolded proteins. Using different biochemical and biophysical approaches, we show that N-TAIL is indeed unstructured in solution. In particular, the spectroscopic and hydrodynamic properties of N-TAIL indicate that this protein domain belongs to the premolten globule subfamily within the class of intrinsically disordered proteins. The isolated N-TAIL domain was shown to be able to bind to its physiological partner, the phosphoprotein (P), and to undergo an induced folding upon binding to the C-terminal moiety of P [J. Biol. Chem. 278 (2003) 18638]. Using a computational analysis, we have identified within N-TAIL a putative alpha-helical molecular recognition element (alpha-MoRE, aa 488-499), which could be involved in binding to P via induced folding. We report the bacterial expression and purification of a truncated form of N-TAIL (N-TAIL2, aa 401-488) devoid of the alpha-MoRE. We show that N-TAIL2 has lost the ability to bind to P, thus supporting the hypothesis that the alpha-MoRE may play a role in binding to P. We have further analyzed the alpha-helical propensities of N-TAIL2 and N-TAIL using circular dichroism in the presence of 2,2,2-trifluoroethanol. We show that N-TAIL2 has a lower alpha-helical potential compared to N-TAIL, thus suggesting that the alpha-MoRE may be indeed involved in the induced folding of N-TAIL. (C) 2003 Elsevier B.V. All rights reserved.