2'3'-cGAMP (sodium salt)

2′,3′-Cyclic GMP-AMP (2′3′-cGAMP, CAS: 2734858-36-5) is the cyclic dinucleotide produced by cyclic GMP-AMP synthase (cGAS). The molecule couples one GMP and one AMP through two asymmetric phosphodiester bonds - one 2′,5′ and one 3′,5′ - which distinguishes it from the symmetric 2′2′- and 3′3′-cGAMP diastereomers.

Double-stranded DNA induces cGAS dimerization, and cGAS then uses GTP and ATP as substrates to form the linear intermediate pppG(2′,5′)pA(3′,5′), which it closes through an intramolecular cyclization into the cyclic dinucleotide bearing both 2′,5′ and 3′,5′ phosphodiester bonds. The synthesized 2′3′-cGAMP diffuses and binds STING on the ER membrane: it inserts into the V-shaped pocket of the STING ligand-binding domain, STING dimerizes and changes conformation, and the complex translocates to the Golgi via the secretory pathway. Oligomerized STING recruits and activates TBK1 at the membrane; activated TBK1 phosphorylates IRF3 and IKKβ, launching type I interferon and NF-κB-dependent inflammatory transcription.

Researchers use 2′3′-cGAMP as a positive control for STING activation to test cellular responses to STING and its downstream effectors: exogenous 2′3′-cGAMP induces IFN-β expression in wild-type cells, whereas this response vanishes in STING-knockout or knockdown cells, distinguishing STING-dependent from STING-independent antiviral signaling. As an adjuvant, 2′3′-cGAMP induces type I interferons through the cGAS-STING pathway and enhances antigen cross-presentation by dendritic cells; it is commonly co-administered with antigen after encapsulation in liposomes or polymeric nanoparticles, raising antigen-specific CD8⁺ T-cell responses and neutralizing antibody titers. In addition, 2′3′-cGAMP crosses the plasma membrane and spreads between cells, thereby activating STING in neighboring bystander cells. However, free 2′3′-cGAMP is rapidly degraded by extracellular phosphodiesterases, and its inherent negative charge limits spontaneous membrane permeation. Consequently, 2′3′-cGAMP cannot maintain an effective concentration in vivo for long, so researchers mostly treat cells in vitro or encapsulate it in adjuvants for local delivery, and rarely use it for prolonged systemic in vivo administration.

References:

Sun L, Wu J, Du F, Chen X, Chen ZJ. Cyclic GMP-AMP synthase is a cytosolic DNA sensor that activates the type I interferon pathway. Science. 2013;339(6121):786-791.

Gao P, Ascano M, Wu Y, et al. Cyclic [G(2′,5′)pA(3′,5′)p] is the metazoan second messenger produced by DNA-activated cyclic GMP-AMP synthase. Cell. 2013;153(21):1094-1107.

Ablasser A, Goldeck M, Cavlar T, et al. cGAS produces a 2′-5′ linked cyclic dinucleotide second messenger that activates STING. Nature. 2013;498(7454):380-384.

Zhang X, Shi H, Wu J, et al. Cyclic GMP-AMP containing mixed phosphodiester linkages is an endogenous high-affinity ligand for STING. Molecular Cell. 2013;51(2):226-235.

Zhong B, Yang Y, Li S, et al. The adaptor protein MITA links virus-sensing receptors to IRF3 transcription factor activation. Immunity. 2008;29(4):538-550.

Khiar S, Quintás-Casas A, Garcin D, et al. 2′3′-cGAMP is a beacon for intracellular DNA sensing. Scientific Reports. 2017;7:4295.

Civril F, Deimling T, de Oliveira Mann CC, et al. Structural mechanism of cytosolic DNA sensing by cGAS. Nature. 2013;498(7454):332-337.