No abstract

Intrinsically disordered proteins (IDPs) defy the structure-function paradigm as they fulfill essential biological functions while lacking well-defined secondary and tertiary structures. Conformational and spectroscopic analyses showed that IDPs do not constitute a uniform family, and can be divided into subfamilies as a function of their residual structure content. Residual intramolecular interactions are thought to facilitate binding to a partner and then induced folding. Comprehensive information about experimental approaches to investigate structural disorder and induced folding is still scarce. We herein provide hints to readily recognize features typical of intrinsic disorder and review the principal techniques to assess structural disorder and induced folding. We describe their theoretical principles and discuss their respective advantages and limitations. Finally, we point out the necessity of using different approaches and show how information can be broadened by the use of multiples techniques.

The nucleoprotein of measles virus consists of an Nterminal moiety, N CORE , resistant to proteolysis and a C-terminal moiety, N TAIL , hypersensitive to proteolysis and not visible as a distinct domain by electron microscopy. We report the bacterial expression, purification, and characterization of measles virus N TAIL . Using nuclear magnetic resonance, circular dichroism, gel filtration, dynamic light scattering, and small angle x-ray scattering, we show that N TAIL is not structured in solution. Its sequence and spectroscopic and hydrodynamic properties indicate that N TAIL belongs to the premolten globule subfamily within the class of intrinsically disordered proteins. The same epitopes are exposed in N TAIL and within the nucleoprotein, which rules out dramatic conformational changes in the isolated N TAIL domain compared with the full-length nucleoprotein. Most unstructured proteins undergo some degree of folding upon binding to their partners, a process termed "induced folding." We show that N TAIL is able to bind its physiological partner, the phosphoprotein, and that it undergoes such an unstructured-to-structured transition upon binding to the C-terminal moiety of the phosphoprotein. The presence of flexible regions at the surface of the viral nucleocapsid would enable plastic interactions with several partners, whereas the gain of structure arising from induced folding would lead to modulation of these interactions. These results contribute to the study of the emerging field of natively unfolded proteins.