Scaffold proteins play an essential role in cellular communication by controlling the assembly of multiple partners involved in signalling pathways. In the JNK pathway, the intrinsically disordered scaffold protein POSH is involved in the initiation of apoptosis, a process triggered by its binding to the small GTPase Rac1. Researchers from the IBS (SIGNAL group), the IAB (A. Palencia), and the ENS Paris (G. Bouvignies) have combined NMR spectroscopy and X-ray crystallography to study the interaction between POSH and Rac1. Their work shows that POSH follows a hierarchical folding pathway upon binding to Rac1, during which different molecular recognition elements become structured sequentially.
The researchers then investigated the interaction of POSH with a Rac1 variant called Rac1b, which is implicated in the development of certain cancers. Rac1b contains a 19-amino-acid insertion resulting from alternative splicing. They showed that this insertion increases the dynamics of Rac1b and alters its recognition by POSH. Thus, Rac1b binds to POSH with slower association and faster dissociation kinetics, while POSH undergoes only partial folding during the interaction. These findings illustrate how alternative splicing of an interaction partner can reconfigure signalling networks by altering the way an intrinsically disordered protein recognizes its partner and folds during their interaction.
Hierarchical folding-upon-binding of an intrinsically disordered protein. Kjaer L, Ielasi F, Winbolt T, Delaforge E, Tengo M, Bessa L, Mariño Pérez L, Boeri Erba E, Bouvignies G, Palencia A, Jensen M. Nat. Commun. 2025 ; 16 : 11346.
Alternative splicing of a structured partner alters the folding-upon-binding trajectory of an intrinsically disordered protein. Kjaer L, Ielasi F, Winbolt T, Delaforge E, Tengo M, Nebl S, Bouvignies G, Palencia A, Jensen M. J. Am. Chem. Soc. 2026 ; 148 : 28401-28413.
Contact : Malene R. Jensen (IBS/Structural Dynamics of Signalling Complexes Group)
Fundings : Impulscience & ANR ScaffoldDisorder