The C-terminal Domain of the Measles Virus Nucleoprotein Is Intrinsically Disordered and Folds upon Binding to the C-terminal Moiety of the Phosphoprotein

Abstract

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.

Domain organization of the N-terminal portion of hordeivirus movement protein TGBp1

“…On the other hand, natively unfolded domains are often found in proteins capable of self-assembly into large multimeric complexes such as viral capsids and nucleocapsids (Namba, 2001). Natively unfolded domains both prevent unwanted spontaneous assembly of such proteins, as has been shown for the measles virus nucleoprotein (Longhi et al, 2003), and stabilize multimeric complexes due to folding upon interaction with the correct partners (Namba, 2001). …”

Functional Anthology of Intrinsic Disorder. 3. Ligands, Post-Translational Modifications, and Diseases Associated with Intrinsically Disordered Proteins

“…Indeed, the C-terminal domain of the nucleoprotein (N tail ) of measles virus, which is involved in a number important functions, is intrinsically unstructured. [22][23][24][25] Metal-thiolate clusters-Several proteins known as metallothioneins rely on metal-thiolate clusters in their functions. There are at least ten known closely related metallothionein proteins expressed in humans.…”

Crystal Structure of the Measles Virus Phosphoprotein Domain Responsible for the Induced Folding of the C-terminal Domain of the Nucleoprotein

“…It is monomeric and consists of a flexible linker (aa 474 -517) fused to the X domain (XD) (aa 517-568). This linker is probably conserved also in MV PCT, as suggested by its high protease sensitivity (16).…”

“…We have recently reported that MV PCT is responsible for the induced folding of N TAIL (16). The induced folding of N TAIL in the presence of its physiological partner opens new perspectives in the structural study of disordered regions within the MV replicative complex.…”

“…it lacks any constant secondary structure in physiological conditions) (16) and protrudes from the surface of viral nucleocapsids (17,18). The presence of flexible regions exposed at the surface of the viral nucleocapsid would ideally favor the interaction with different viral partners.…”