An Alternative Phosphorylation Switch in Integrin β2 (CD18) Tail for Dok1 Binding

Area of Science:

• Cellular and Molecular Biology
• Immunology
• Protein-protein Interactions

Background:

• Integrins are crucial for cell adhesion and migration, mediating cellular responses through interactions with cytoplasmic tail-binding proteins.
• Dok1 negatively regulates integrin activation by binding to phosphorylated NxxY motifs in integrin β tails, but its interaction with β2 integrins, lacking this motif, was unclear.

Purpose of the Study:

• To elucidate the mechanism by which Dok1 associates with integrin β2 tails.
• To identify specific residues and phosphorylation events in the integrin β2 tail responsible for Dok1 binding.

Main Methods:

• Nuclear Magnetic Resonance (NMR) spectroscopy to analyze protein-protein interactions and binding affinities.
• Cell-based assays to validate Dok1-integrin β2 interactions in a cellular context.
• Computational docking to model the structural complex of Dok1 and the integrin β2 tail.

Main Results:

• Specific serine residues (Ser745 and Ser756) in the integrin β2 tail, adjacent to the NxxF motif, were identified as critical for Dok1 interaction.
• NMR analysis revealed higher affinity binding of Dok1's phospho-tyrosine binding (PTB) domain to a β2 tail peptide phosphorylated at Ser756 (pSer756) compared to pSer745.
• Docked structural models indicated that the phosphorylated β2 tail peptide binds to the canonical ligand-binding pocket of Dok1.

Conclusions:

• The study proposes an alternative phosphorylation-dependent mechanism for Dok1 binding to β2 integrins, distinct from the canonical NxxY motif.
• This novel regulatory switch involving pSer756 in β2 integrins may play a significant role in modulating immune cell functions.
• Findings provide new insights into integrin signaling pathways relevant to immune cell adhesion, migration, and activation.