Novel c-di-GMP recognition modes of the mouse innate immune adaptor protein STING

• Main Authors: Chin, Ko-Hsin, Tu, Zhi-Le, Su, Yi-Che, Yu, Yu-Jen, Chen, Hui-Chen, Lo, Yuan-Chao, Chen, Chin-Pan, Chuah, Mary Lay-Cheng, Liang, Zhao-Xun, Chou, Shan-Ho, Barber, Glen N.
• Other Authors: School of Biological Sciences
• Format: Article
• Language: English
• Published: 2013
• Subjects: DRNTU::Science::Biological sciences
• Online Access: https://hdl.handle.net/10356/100596; http://hdl.handle.net/10220/10980
• Institution: Nanyang Technological University

The mammalian ER protein STING (stimulator of interferon genes; also known as MITA, ERIS, MPYS or TMEM173) is an adaptor protein that links the detection of cytosolic dsDNA to the activation of TANK-binding kinase 1 (TBK1) and its downstream transcription factor interferon regulatory factor 3 (IFN3). Recently, STING itself has been found to be the direct receptor of bacterial c-di-GMP, and crystal structures of several human STING C-terminal domain (STING-CTD) dimers in the apo form or in complex with c-di-GMP have been published. Here, a novel set of structures of mouse STING-CTD (mSTING137-344) in apo and complex forms determined from crystals obtained under different crystallization conditions are reported. These novel closed-form structures exhibited considerable differences from previously reported open-form human STING-CTD structures. The novel mSTING structures feature extensive interactions between the two monomers, a unique asymmetric c-di-GMP molecule with one guanine base in an unusual syn conformation that is well accommodated in the dimeric interface with many direct specific interactions and two unexpected equivalent secondary peripheral c-di-GMP binding sites. Replacement of the amino acids crucial for specific c-di-GMP binding in mSTING significantly changes the ITC titration profiles and reduces the IFN-[beta] reporter luciferase activity. Taken together, these results reveal a more stable c-di-GMP binding mode of STING proteins that could serve as a template for rational drug design to stimulate interferon production by mammalian cells.