Gharpure Anant, Sulpizio Ariana, Loeffler Johannes R, Fernández-Quintero Monica L, Tran Andy S, Lairson Luke L, Ward Andrew B
Department of Integrative Structural and Computational Biology, Scripps Research, La Jolla, CA, USA.
Department of Chemistry, Scripps Research, La Jolla, CA, USA.
Nat Commun. 2025 Apr 11;16(1):3440. doi: 10.1038/s41467-025-58641-5.
STING plays essential roles coordinating innate immune responses to processes that range from pathogenic infection to genomic instability. Its adaptor function is activated by cyclic dinucleotide (CDN) secondary messengers originating from self (2'3'-cGAMP) or bacterial sources (3'3'-CDNs). Different classes of CDNs possess distinct binding modes, stabilizing STING's ligand-binding domain (LBD) in either a closed or open conformation. The closed conformation, induced by the endogenous ligand 2'3'-cGAMP, has been extensively studied using cryo-EM. However, significant questions remain regarding the structural basis of STING activation by open conformation-inducing ligands. Using cryo-EM, we investigate potential differences in conformational changes and oligomeric assemblies of STING for closed and open conformation-inducing synthetic agonists. While we observe a characteristic 180° rotation for both classes, the open-LBD inducing agonist diABZI-3 uniquely induces a quaternary structure reminiscent but distinct from the reported autoinhibited state of apo-STING. Additionally, we observe slower rates of activation for this ligand class in functional assays, which collectively suggests the existence of a potential additional regulatory mechanism for open conformation-inducing ligands that involves head-to-head interactions and restriction of curved oligomer formation. These observations have potential implications in the selection of an optimal class of STING agonist in the context of a defined therapeutic application.
STING在协调从病原体感染到基因组不稳定等一系列过程的先天免疫反应中发挥着重要作用。其衔接蛋白功能由源自自身（2'3'-cGAMP）或细菌来源（3'3'-环二核苷酸）的环二核苷酸（CDN）第二信使激活。不同类别的CDN具有不同的结合模式，可使STING的配体结合结构域（LBD）稳定在封闭或开放构象中。由内源性配体2'3'-cGAMP诱导的封闭构象已通过冷冻电镜进行了广泛研究。然而，关于开放构象诱导配体激活STING的结构基础仍存在重大问题。我们使用冷冻电镜研究了封闭和开放构象诱导合成激动剂作用下STING在构象变化和寡聚体组装方面的潜在差异。虽然我们观察到两类激动剂都有180°的特征性旋转，但开放LBD诱导激动剂diABZI-3独特地诱导了一种四级结构，这种结构让人联想到但不同于已报道的无配体STING的自抑制状态。此外，我们在功能试验中观察到这类配体的激活速率较慢，这共同表明存在一种潜在的额外调节机制，用于开放构象诱导配体，该机制涉及头对头相互作用和对弯曲寡聚体形成的限制。这些观察结果对于在特定治疗应用背景下选择最佳类别的STING激动剂具有潜在意义。
