NSRRC Activity Report 2022

Life Science 047 antibody binding ( Fig. 2(d) ). This finding supported the hypothesis that removing or trimming down the glycan shield of the spike antigen could elicit different immune responses against SARS-CoV-2 and greater efficacy against VOCs. In summary, trimming the glycan shield of the spike protein to mono-GlcNAc glycoform enabled the conserved epitopes to be exposed to the immune system, leading to improved elicitation of more effective and broadly protective immune response against SARS-CoV-2 VOCs. Moreover, taking the broadly neutralizing m31A7 antibody in this study as an example, these targeted conserved epitopes could facilitate next-generation vaccine antigen design and development. (Reported by Han-Yi Huang, École Polytechnique Fédérale de Lausanne, Switzerland) This report features the work of research groups led by Chi-Huey Wong, Che Ma and Kuo-I Lin published in Sci. Transl. Med. 14 , eabm0899 (2022). TLS 15A1 Biopharmaceuticals Protein Crystallography • X-ray Crystallography, Biological Macromolecules • Protein Structures, Nucleotides, Viral Defense, Life Science Reference 1. H.-Y. Huang, H.-Y. Liao, X. Chen, S.-W. Wang, C.-W. Cheng, M. Shahed-Al-Mahmud, Y.-M. Liu, A. Mohapatra, T.-H. Chen, J. M. Lo, Y.-M. Wu, H.-H. Ma, Y.-H. Chang, H.-Y. Tsai, Y.-C. Chou, Y.-P. Hsueh, C.-Y. Tsai, P.-Y. Huang, S.-Y. Chang, T.-L. Chao, H.-C. Kao, Y.-M. Tsai, Y.-H. Chen, C.-Y. Wu, J.-T. Jan, T.-J. R. Cheng, K.-I. Lin, C. Ma, C.-H. Wong, Sci. Transl. Med. 14 , eabm0899 (2022). How Binding of CDN to STING Reduces Phage Propagation in Bacteria This crystallographic analysis of the complex structures of PcSTING and MySTING with cyclic di-GMP elucidated how cyclic dinucleotide (CDN) was recognized and revealed the driving force behind filament formation. M ammalian STimulator of INterferon Genes (STING) is essential to innate immunity. During viral infection, the enzyme cyclic GMP–AMP synthase (cGAS) acts as a sensor that rapidly recognizes foreign nucleic acid molecules and synthesizes 2’3’-cGAMP as a second messenger. The binding of 2’3’-cGAMP to the STING dimer triggers its further oligomerization into filamentous structures, which in turn activate downstream effectors. Similarly, to combat viruses, the cyclic-oligonucleotide- based antiphage signaling system 1 in the bacterial arsenal consists of a cGAS/DncV-like nucleotidyltransferase (CD-NTase) that synthesizes diverse cyclic dinucleotide (CDN) and cyclic trinucleotide second messengers upon phage infection and an effector protein that binds to the CD-NTase product and induces programmed cell death through its various activities. The signaled suicide commitment serves as a defense strategy that restricts phage propagation. Recently, STING protein was revealed to be enlisted by bacteria. 2 In fact, eukaryotic STING has an origin in bacteria. Although mammalian STING has been investigated in detail, the three-dimensional structure of bacterial STING, the precise mode through which CDN binds to the dimeric protein, and the specific recognition mechanism have not yet been elucidated. In this work, a research team led by Yeh Chen (China Medical University) determined the C-terminal domain structures of Pc STING from Prevotella corporis and My STING from Myroides sp. ZB35 by using multiwavelength anomalous dispersion and molecular replacement methods with data collected from SeMet-labeled and CDN-bound crystals at beamlines TPS 05A , TPS 07A , and TLS 15A1 of the NSRRC. 3 The crystals of Pc STING and My STING belong to the space groups P2 1 2 1 2 and P2 1 , respectively; in both these groups, an asymmetric unit contains one dimer. The structures were refined to 2.25 and 2.17-Å resolution, and the coordinates were deposited in the PDB under accession codes 7EBD and 7EBL. The protomers in the Pc STING and My STING crystals had root-mean-square deviations (RMSDs) of 0.29 and 0.64 Å for 158 and 160 matched Cα pairs, respectively, with the STING domain forming canonical V-shaped dimers ( Figs. 1(a) and 1(b) , see next page). Each protomer has a mixed α/β fold with a central five-stranded β-sheet surrounded by five α-helices and a flanking β-ribbon.