cGAS bends unpaired DNA to form an unconventional structure that hyperactivates the innate immune response

Shuangshuang Yang; Shuai Wu; Silian Chen; Xin Li; Iryna Chelepis; Smaranda Willcox; Katherine Camille Barnett; Xiaoqing Hu; Guannan Huang; W. June Brickey; Joseph A. Duncan; Wei-Chun Chou; Pengda Liu; William G. Fusco; Stephanie Torres; Gerald S. Shadel; Gregory D. Bowman; Jack D. Griffith; Jungsan Sohn; Jenny P.‐Y. Ting

doi:10.64898/2026.05.22.726336

ImmunologybioRxivMay 25, 2026

Preprint

cGAS bends unpaired DNA to form an unconventional structure that hyperactivates the innate immune response

Shuangshuang Yang iD, Shuai Wu, Silian Chen iD, Xin Li, Iryna Chelepis, Smaranda Willcox iD, Katherine Camille Barnett iD, Xiaoqing Hu, Guannan Huang, W. June Brickey iD, Joseph A. Duncan iD, Wei-Chun Chou iD, Pengda Liu iD, William G. Fusco iD, Stephanie Torres, Gerald S. Shadel iD, Gregory D. Bowman iD, Jack D. Griffith iD, Jungsan Sohn iD, Jenny P.‐Y. Ting iD

Abstract

cGAS is a pattern-recognition receptor for dsDNA and forms 2cGAS:2DNA dimers followed by oligomerization into phase-separated condensates when fully-complementary DNA is studied. However, many DNAs are not fully complementary. We report that DNA with unpaired regions such as those found during transcription, recombination or replication (designated as bubble-DNA, Bu-DNA) causes cGAS hyper-activation. Hyperactivation is observed by Bu-DNA embedded in linear DNA, circular DNA, plasmid DNA and mitochondria DNA. Bu-DNA binds significantly more tightly to the cGAS catalytic domain than paired-DNA but suppresses condensation. Cryo-EM and single-molecule FRET reveal that cGAS forms 2cGAS:1DNA complexes by bending Bu-DNA into a V-shape using the unpaired region as a hinge, limiting its oligomeric state. This uncovers a novel mode of cGAS activation attributed to pattern diversity within pattern ligands.

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