Cyclic GMP-AMP synthase is activated by double-stranded DNA-induced oligomerization

Area of Science:

• Immunology
• Molecular Biology
• Biochemistry

Background:

• Cyclic GMP-AMP synthase (cGAS) is a key sensor of cytosolic DNA, initiating innate immune responses.
• cGAS activation leads to the production of type I interferons (IFN-β) via the STING-TBK1-IRF-3 pathway.

Purpose of the Study:

• To elucidate the structural and mechanistic basis of cGAS activation by double-stranded DNA (dsDNA).
• To investigate the role of specific DNA binding sites in cGAS function and activation.

Main Methods:

• X-ray crystallography to determine the structure of mouse cGAS bound to dsDNA and 2',5' cGAMP.
• Enzyme assays and IFN-β reporter assays using cGAS mutants.
• Mutagenesis and DNA binding studies.

Main Results:

• Mouse cGAS forms a 2:2 complex with an 18 bp dsDNA, interacting through two distinct binding sites.
• Cooperative binding of dsDNA at both sites is essential for cGAS activation, with site B playing a critical role.
• Structural data provided insights into the catalytic mechanism of cGAS.

Conclusions:

• cGAS activation is triggered by dsDNA-induced oligomerization.
• Understanding cGAS structure-function relationships is crucial for innate immunity research.