title: Plasticity in PYD assembly revealed by cryo-EM structure of the PYD filament of AIM2.
abstract: Absent in melanoma 2 (AIM2) is an essential cytosolic double-stranded DNA receptor that assembles with the adaptor, apoptosis-associated speck-like protein containing a caspase recruitment domain (ASC), and caspase-1 to form the AIM2 inflammasome, which leads to proteolytic maturation of cytokines and pyroptotic cell death. AIM2 contains an N-terminal Pyrin domain (PYD) that interacts with ASC through PYD/PYD interactions and nucleates ASCPYDfilament formation. To elucidate the molecular basis of AIM2-induced ASCPYDpolymerization, we generated AIM2PYDfilaments fused to green fluorescent protein (GFP) and determined its cryo-electron microscopic (cryo-EM) structure. The map showed distinct definition of helices, allowing fitting of the crystal structure. Surprisingly, the GFP-AIM2PYDfilament is a 1-start helix with helical parameters distinct from those of the 3-start ASCPYDfilament. However, despite the apparent symmetry difference, helical net and detailed interface analyses reveal minimal changes in subunit packing. GFP-AIM2PYDnucleated ASCPYDfilament formation in comparable efficiency as untagged AIM2PYD, suggesting assembly plasticity in both AIM2PYDand ASCPYD. The DNA-binding domain of AIM2 is able to form AIM2/DNA filaments, within which the AIM2PYDis brought into proximity to template ASCPYDfilament assembly. Because ASC is able to interact with many PYD-containing receptors for the formation of inflammasomes, the observed structural plasticity may be critically important for this versatility in the PYD/PYD interactions.
authors.affiliation: Department of Biological Chemistry and Molecular Pharmacology, Harvard Medical School, Boston, MA, USA ; Program in Cellular and Molecular Medicine, Boston Children's Hospital, Boston, MA, USA.
authors.forename: Alvin
authors.initials: A
authors.lastname: Lu
authors.affiliation: Department of Biological Chemistry and Molecular Pharmacology, Harvard Medical School, Boston, MA, USA ; Program in Cellular and Molecular Medicine, Boston Children's Hospital, Boston, MA, USA.
authors.forename: Yang
authors.initials: Y
authors.lastname: Li
authors.affiliation: Department of Biological Chemistry and Molecular Pharmacology, Harvard Medical School, Boston, MA, USA ; Program in Cellular and Molecular Medicine, Boston Children's Hospital, Boston, MA, USA.
authors.forename: Qian
authors.initials: Q
authors.lastname: Yin
authors.affiliation: Department of Biological Chemistry and Molecular Pharmacology, Harvard Medical School, Boston, MA, USA ; Program in Cellular and Molecular Medicine, Boston Children's Hospital, Boston, MA, USA.
authors.forename: Jianbin
authors.initials: J
authors.lastname: Ruan
authors.affiliation: Department of Biochemistry and Molecular Genetics, University of Virginia, Charlottesville, VA, USA.
authors.forename: Xiong
authors.initials: X
authors.lastname: Yu
authors.affiliation: Department of Biochemistry and Molecular Genetics, University of Virginia, Charlottesville, VA, USA.
authors.forename: Edward
authors.initials: E
authors.lastname: Egelman
authors.affiliation: Department of Biological Chemistry and Molecular Pharmacology, Harvard Medical School, Boston, MA, USA ; Program in Cellular and Molecular Medicine, Boston Children's Hospital, Boston, MA, USA.
authors.forename: Hao
authors.initials: H
authors.lastname: Wu
keywords: AIM2 PYD filament; ASC-dependent inflammasome; Death Domain interaction; cryo-EM; helical reconstruction; inflammasome; nucleated polymerization; plasticity