Distinct oligomeric assemblies of STING induced by non-nucleotide agonists

Area of Science:

• Immunology
• Structural Biology
• Molecular Biology

Background:

• STING (stimulator of interferon genes) is crucial for innate immunity, responding to pathogens and genomic instability.
• STING activation relies on cyclic dinucleotide (CDN) secondary messengers, which stabilize its ligand-binding domain (LBD) in either closed or open conformations.
• While the closed conformation is well-studied, the structural basis of STING activation by open conformation-inducing ligands remains unclear.

Purpose of the Study:

• To investigate structural differences in STING activation by closed versus open conformation-inducing synthetic agonists using cryo-electron microscopy (cryo-EM).
• To elucidate the conformational changes and oligomeric assemblies of STING induced by different CDN classes.

Main Methods:

• Cryo-electron microscopy (cryo-EM) was employed to determine the structures of STING bound to closed and open conformation-inducing agonists.
• Functional assays were conducted to assess the kinetics of STING activation by these different ligand classes.

Main Results:

• Both closed and open conformation-inducing agonists induced a characteristic 180° rotation in STING.
• An open-LBD inducing agonist, diABZI-3, uniquely formed a quaternary structure distinct from the apo-STING autoinhibited state.
• Ligands inducing the open conformation exhibited slower activation rates and suggested a regulatory mechanism involving head-to-head interactions and restricted oligomer formation.

Conclusions:

• STING activation by open conformation-inducing ligands involves unique structural rearrangements and regulatory mechanisms.
• These findings suggest distinct therapeutic potentials for different classes of STING agonists.
• Understanding these differences is critical for optimizing STING agonist selection for specific therapeutic applications.