The cGAS-STING signaling pathway is an essential component of the innate immune system that plays a critical role in detecting and responding to microbial infections [1,2]. The pathway is activated by the recognition of cytosolic DNA by the sensor protein cGAS, which leads to the production of cyclic GMP-AMP (cGAMP) [[3], [4], [5], [6]]. cGAMP then binds to and activates the downstream effector protein STING [7]. Activated STING then recruits and activates the kinase TBK1, which phosphorylates and activates Interferon Regulatory Factor 3 (IRF3) [8,9]. IRF3 translocates to the nucleus and induces the expression of type I interferons and other cytokines, which play a critical role in host defense against viral and bacterial infections [10,11].

Dysregulation of the STING protein has been associated with multiple diseases. A systematic summary of STING's roles in the pathogenesis of various diseases, including inflammatory, autoimmune, and cancer, among others, was provided in recent reviews by Patel and Jin [12], as well as Zhang et al [13]. Based on current knowledge in many tumor-relevant diseases, the dysregulation of STING mainly manifests as a change in the expression level of STING (upregulation or downregulation), while somatic mutations of STING are rare. One relatively notable mutation is G251E, which was found in skin-face basal cell carcinoma. The best-known somatic mutation in STING is found in STING-associated vasculopathy with onset in infancy (SAVI), an exceedingly rare disease caused by mutations in STING at residues 147, 154, and 155 [14]. In SAVI, the mutated STING protein is persistently activated, leading to chronic inflammation, blood vessel damage, and organ dysfunction. Given the potential implications of STING in various diseases, it has emerged as a promising therapeutic target for treating illnesses such as cancer, autoimmune disorders, and viral infections [[15], [16], [17], [18], [19], [20]].

Structural studies have yielded significant insights into the activation mechanism of STING [[21], [22], [23]]. STING forms a butterfly-shaped dimer, with each subunit consisting of two domains: a ligand-binding domain (LBD) and a transmembrane domain (TMD). A two-turn connector helix (residues 137–150) and a connector loop (residues 151–153) connect the two domains. The dimeric LBD undergoes a conformational change upon ligand binding of cyclic GMP-AMP (cGAMP), rotating about 180 ° from its inactive to active state. This activated STING subsequently triggers various downstream signaling pathways, including the type I interferon pathway.

Although we have gained a considerable amount of knowledge regarding STING activation, there is still a lack of understanding regarding the specific role of each component in the transition process and the impact of critical mutations. In this study, we utilized atomistic simulations to uncover a more detailed mechanism of STING transition, including the energetic and mechanistic factors driving the process.