Structural mechanism of cytosolic DNA sensing by cGAS

Abstract

Summary Cytosolic DNA arising from intracellular bacteria or viral infections is a powerful pathogen-associated molecular pattern (PAMP) that leads to innate immune host defense by the production of type I interferon and inflammatory cytokines. Recognition of cytosolic DNA by the recently discovered cyclic-GMP-AMP (cGA) synthase (cGAS) induces the production of cGA to activate the stimulator of interferon genes (STING). Here we report the crystal structure of cGAS alone and in complex with DNA, ATP and GTP along with functional studies. Our results explain cGAS’ broad specificity DNA sensing, show how cGAS catalyzes di-nucleotide formation and indicate activation by a DNA-induced structural switch. cGAS possesses a remarkable structural similarity to the antiviral cytosolic dsRNA sensor 2’-5’oligoadenylate synthase (OAS1), but contains a unique zinc-thumb that recognizes B-form dsDNA. Our results mechanistically unify dsRNA and dsDNA innate immune sensing by OAS1 and cGAS nucleotidyl transferases.

Cutting Edge: Antimalarial Drugs Inhibit IFN-β Production through Blockade of Cyclic GMP-AMP Synthase–DNA Interaction

“…1B): Sites A and B. The more pronounced Site A interactions are defined through extensive contact with a positively charge surface of the protein flanked by an a-helical spine and Zn-thumb (20). Site B is structurally located opposite from Site A on the adjacent protein monomer (21).…”

Crystal structure of the novel di-nucleotide cyclase from Vibrio cholerae (DncV) responsible for synthesizing a hybrid cyclic GMP-AMP

“…As shown by previous studies [5,10,14], cGASs adopt a bilobal scaffold with mixed α/β topology, which represents a structural characteristic of members of the NTase superfamily. However, cGASs cannot execute di-nucleotide cyclization function in the absence of an activator dsDNA.…”

“…Structural, biochemical and cellular studies reveal that upon dsDNA binding, cGAS is activated through formation of a catalytically competent conformation [5,6]. dsDNA binding can be disrupted by ablation of interactions with two or three successive phosphodiesters in either DNA strand, which results in impaired or completely abrogated cGAS function and in turn negatively impacts type I interferon production [6].…”

“…Similar to the formation of c-di-GMP, cGAMP is likely to be generated in a stepwise manner, involving an initial formation of G(2′,5′)pA linkage followed by A(3′,5′)pG generation. These sequential reactions lead to the formation of the pair of phosphodiester linkages with two molecules of pyrophosphate released as byproducts [5,6].…”

“…Three secondary structures, α7, α8 and α9, of DncV were labeled out. (D) Comparison of the key residues of active sites from DncV, inactive (PDB code: 4K8V) and active (PDB code: 4K9B) murine cGAS [6], inactive (PDB code: 4JLX) and active porcine cGAS (PDB code: 4KB6) [5], inactive porcine (PDB code: 1PX5) [12] and active human OAS1 (PDB code: 4IG8) [15], and inactive human cGAS (PDB code: 4KM5) [10]. (E) Key residues responsible for DncV activity.…”