Partner-Mediated Polymorphism of an Intrinsically Disordered Protein

Area of Science:

• Biochemistry
• Structural Biology
• Virology

Background:

• Intrinsically disordered proteins (IDPs) lack stable structures but recognize partners via molecular recognition elements (MoREs).
• The measles virus nucleoprotein's C-terminal intrinsically disordered domain (N_TAIL) contains a MoRE that binds both the viral X domain (XD) and heat shock protein 70 (hsp70).
• Structural information for the N_TAIL/hsp70 complex is lacking, and the binding mechanisms to different partners are not fully understood.

Purpose of the Study:

• To investigate the binding mechanisms of the N_TAIL MoRE to both XD and hsp70.
• To determine if the N_TAIL MoRE adopts a consistent structure when binding to different partners.
• To explore the concept of partner-mediated polymorphism in IDPs.

Main Methods:

• Utilized mutational studies to probe the N_TAIL MoRE.
• Employed a protein complementation assay based on green fluorescent protein (GFP) reconstitution to quantify binding affinities.
• Analyzed changes in α-helicity of the MoRE in relation to binding.

Main Results:

• The N_TAIL MoRE binds both XD and hsp70, but through distinct mechanisms.
• Hsp70 binding is more tolerant to MoRE substitutions than XD binding, with most substitutions increasing binding strength.
• Unlike XD binding, hsp70 binding is largely unaffected by the α-helicity of the N_TAIL MoRE, suggesting a non-α-helical bound conformation.

Conclusions:

• The N_TAIL MoRE exhibits partner-mediated structural polymorphism, adopting different conformations depending on the binding partner.
• The pre-recognition α-helical state of the N_TAIL MoRE does not dictate its bound conformation.
• This study provides insights into how IDPs achieve specific recognition of diverse partners through adaptable binding mechanisms.