An electrostatic network with strong connectivity is a phospho-sensor for regulating affinity of Syk-receptor...

Area of Science:

• Molecular immunology
• Protein dynamics
• Biophysics

Background:

• Spleen tyrosine kinase (Syk) is crucial for immune signaling, acting downstream of membrane receptors.
• Syk's tandem SH2 (tSH2) domain regulates its activity through association with phosphorylated motifs on immunoreceptors.
• Phosphorylation at Y131 on the tSH2 linker influences this critical protein-protein interaction.

Purpose of the Study:

• To elucidate the molecular mechanism by which Y131-phosphorylation regulates Syk tSH2 domain association.
• To investigate the role of interdomain dynamics and electrostatic networks in Syk regulation.

Main Methods:

• Long-timescale molecular dynamics (MD) simulations of unphosphorylated and Y131-phosphorylated Syk tSH2.
• Analysis of interdomain electrostatic networks and conformational landscapes.
• NMR spectroscopy to assess salt dependence of domain-domain coupling.

Main Results:

• Unphosphorylated Syk tSH2 exhibits a highly correlated interdomain electrostatic network, leading to a narrow conformational free energy landscape.
• Y131-phosphorylation disrupts this network, broadening the free energy landscape and enabling alternative interdomain conformations.
• NMR data confirm the electrostatic nature of tSH2 domain-domain coupling and its sensitivity to salt concentration.

Conclusions:

• Syk tSH2 functions as a phospho-sensor, with Y131-phosphorylation modulating its conformational plasticity.
• This phosphorylation-induced change in dynamics is mediated by disruption of an interdomain electrostatic network.
• The findings reveal a unique, entropically driven regulatory mechanism for Syk-immunoreceptor interactions.