The molecular basis of tight nuclear tethering and inactivation of cGAS

Nucleic acids derived from pathogens induce potent innate immune responses 1 – 6 . Cyclic GMP–AMP synthase (cGAS) is a double-stranded DNA sensor that catalyses the synthesis of the cyclic dinucleotide cyclic GMP–AMP, which mediates the induction of type I interferons through the STING–TBK1–IRF3 sig...

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Bibliographic Details
Published in:	Nature (London) Vol. 587; no. 7835; pp. 673 - 677
Main Authors:	Zhao, Baoyu, Xu, Pengbiao, Rowlett, Chesley M., Jing, Tao, Shinde, Omkar, Lei, Yuanjiu, West, A. Phillip, Liu, Wenshe Ray, Li, Pingwei
Format:	Journal Article
Language:	English
Published:	London Nature Publishing Group UK 26-11-2020 Nature Publishing Group
Subjects:	101/28 14 14/19 631/250/262 631/535/1258 82 82/80 Affinity AMP Analysis Animals Binding Binding sites Biocatalysis Catalytic activity Catalytic Domain Cell Line Chemical synthesis Conformation Control Cryoelectron Microscopy Cyclic GMP Deactivation Deoxyribonucleic acid DNA DNA - chemistry DNA - genetics DNA - metabolism DNA - ultrastructure DNA polymerases DNA-ligand interactions Electron microscopy Histones Humanities and Social Sciences Humans Hydrogen bonds Inactivation Innate immunity Interferon Ligands Mice Microscopy Models, Molecular Molecular biology multidisciplinary Mutation Nucleic acids Nucleosomes Nucleosomes - chemistry Nucleosomes - metabolism Nucleosomes - ultrastructure Nucleotidyltransferases - antagonists & inhibitors Nucleotidyltransferases - chemistry Nucleotidyltransferases - genetics Nucleotidyltransferases - metabolism Nucleotidyltransferases - ultrastructure Protein Binding Science Science (multidisciplinary) Signal Transduction Signaling Sperm Tethering United States
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Summary:	Nucleic acids derived from pathogens induce potent innate immune responses 1 – 6 . Cyclic GMP–AMP synthase (cGAS) is a double-stranded DNA sensor that catalyses the synthesis of the cyclic dinucleotide cyclic GMP–AMP, which mediates the induction of type I interferons through the STING–TBK1–IRF3 signalling axis 7 – 11 . cGAS was previously thought to not react with self DNA owing to its cytosolic localization 2 , 12 , 13 ; however, recent studies have shown that cGAS is localized mostly in the nucleus and has low activity as a result of tight nuclear tethering 14 – 18 . Here we show that cGAS binds to nucleosomes with nanomolar affinity and that nucleosome binding potently inhibits its catalytic activity. To elucidate the molecular basis of cGAS inactivation by nuclear tethering, we determined the structure of mouse cGAS bound to human nucleosome by cryo-electron microscopy. The structure shows that cGAS binds to a negatively charged acidic patch formed by histones H2A and H2B via its second DNA-binding site 19 . High-affinity nucleosome binding blocks double-stranded DNA binding and maintains cGAS in an inactive conformation. Mutations of cGAS that disrupt nucleosome binding alter cGAS-mediated signalling in cells. Structural studies show that cyclic GMP–AMP synthase binds to nucleosomes through its DNA-binding site, which maintains it in an inactive conformation and prevents self-DNA binding.
Bibliography:	ObjectType-Article-1 SourceType-Scholarly Journals-1 ObjectType-Feature-2 content type line 23 Author contributions P.L. conceived the study. B.Z. and P.X. expressed the proteins, conducted the binding studies and determined the structures. C.R. prepared the reconstituted nucleosome. T.J. conducted the binding studies, generated and purified the cGAS mutants. O.S. purified the cGAS mutants. Y.L. and A.P.W. studied the nuclear localization of cGAS. B.Z., P.X., W.L. and P.L. wrote the paper. These authors made equal contributions to the work
ISSN:	0028-0836 1476-4687
DOI:	10.1038/s41586-020-2749-z