Conserved salt-bridge competition triggered by phosphorylation regulates the protein interactome

Area of Science:

• Biochemistry
• Molecular Biology
• Structural Biology

Background:

• Phosphorylation is a key post-translational modification regulating protein interactions.
• The precise mechanisms by which phosphorylation controls these interactions remain incompletely understood.
• Raf Kinase Inhibitory Protein (RKIP) is known to regulate signaling pathways.

Purpose of the Study:

• To elucidate the mechanism by which RKIP regulates protein interactions upon phosphorylation.
• To identify novel regulatory strategies for protein-protein interactions.
• To explore the evolutionary conservation and broader applicability of the identified mechanism.

Main Methods:

• Nuclear Magnetic Resonance (NMR) spectroscopy.
• X-ray crystallography.
• Analysis of evolutionary conservation in protein databases.

Main Results:

• A "salt-bridge theft" mechanism was identified, where phosphorylation triggers RKIP to switch partners from Raf-1 to G-protein-coupled receptor kinase 2.
• Phosphoserine directly competes with a lysine residue, initiating local unfolding and promoting new interactions.
• This mechanism is conserved across evolution and present in various homo- and hetero-oligomeric proteins.

Conclusions:

• The salt-bridge theft mechanism provides a facile strategy for regulating protein interactions through solvent-accessible residues.
• This mechanism allows for dynamic control of signaling pathways, bridging MAP kinase and G-Protein-Coupled Receptor cascades.
• The mechanism offers specificity through local unfolding and conformational changes at protein interfaces.