Dynamic control of RSK complexes by phosphoswitch-based regulation.

Area of Science:

• Molecular Biology
• Biochemistry
• Cell Signaling

Background:

• Protein-protein complex assembly/disassembly is dynamically regulated.
• Phosphoswitches utilizing linear motifs are key regulators.
• Extracellular signal-regulated kinase 2 (ERK2) phosphorylates ribosomal S6 kinase 1 (RSK1) for activation.

Purpose of the Study:

• To elucidate the regulatory mechanism of RSK1 C-terminal tail (CTT) phosphorylation.
• To investigate how RSK1 CTT phosphorylation affects protein-binding capacity and dynamics.
• To characterize the structural basis of ERK2-RSK1 and RSK1-substrate complex dissociation.

Main Methods:

• Structural characterization of RSK1 CTT.
• Biochemical assays to assess protein-binding.
• Validation in living cells under epidermal growth factor (EGF) stimulation.

Main Results:

• Autophosphorylation of RSK1 CTT forms an intramolecular charge clamp, masking binding residues.
• This phosphorylation acts as an autoregulated phosphoswitch, modulating protein interactions.
• Structural data reveal mechanisms for rapid dissociation of ERK2-RSK1 and RSK1-PDZ substrate complexes.
• Phosphoswitches can be classified as ON/OFF or dimmer switches based on phosphorylation site positioning.

Conclusions:

• Phosphorylation-induced conformational changes in disordered regions regulate kinase activity and signaling.
• RSK1 CTT functions as a tunable phosphoswitch, controlling its interactions.
• Disordered region phosphorylation and allosteric core events contribute to complex signaling.