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Assembly-driven activation of the AIM2 foreign-dsDNA sensor provides a polymerization template for downstream ASC.

Morrone SR, Matyszewski M, Yu X, Delannoy M, Egelman EH, Sohn J - Nat Commun (2015)

Bottom Line: The ability to oligomerize is critical for binding dsDNA, and in turn permits the size of dsDNA to regulate the assembly of the AIM2 polymers.The AIM2(PYD) oligomers define the filamentous structure, and the helical symmetry of the AIM2(PYD) filament is consistent with the filament assembled by the PYD of the downstream adaptor ASC.Our results suggest that the role of AIM2(PYD) is not autoinhibitory, but generating a structural template by coupling ligand binding and oligomerization is a key signal transduction mechanism in the AIM2 inflammasome.

View Article: PubMed Central - PubMed

Affiliation: Department of Biophysics and Biophysical Chemistry, Johns Hopkins University School of Medicine Baltimore, Maryland 21205, USA.

ABSTRACT
AIM2 recognizes foreign dsDNA and assembles into the inflammasome, a filamentous supramolecular signalling platform required to launch innate immune responses. We show here that the pyrin domain of AIM2 (AIM2(PYD)) drives both filament formation and dsDNA binding. In addition, the dsDNA-binding domain of AIM2 also oligomerizes and assists in filament formation. The ability to oligomerize is critical for binding dsDNA, and in turn permits the size of dsDNA to regulate the assembly of the AIM2 polymers. The AIM2(PYD) oligomers define the filamentous structure, and the helical symmetry of the AIM2(PYD) filament is consistent with the filament assembled by the PYD of the downstream adaptor ASC. Our results suggest that the role of AIM2(PYD) is not autoinhibitory, but generating a structural template by coupling ligand binding and oligomerization is a key signal transduction mechanism in the AIM2 inflammasome.

No MeSH data available.


Related in: MedlinePlus

AIM2PYD is required to assemble filamentous structures on dsDNA.(a) An electron micrograph of AIM2Hin clusters on λdsDNA (b–d) Electron micrographs of wild-type AIM2FL filaments assembled on λdsDNA. (e–j) Electron micrographs of AIM2FL mutants bound to λdsDNA. (k) A cartoon of the AIM2PYD filament and the locations of mutated side chains based on the congruent helical symmetry between AIM2PYD and ASCPYD (see also Fig. 7b). Scale bar, 100 nm.
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f8: AIM2PYD is required to assemble filamentous structures on dsDNA.(a) An electron micrograph of AIM2Hin clusters on λdsDNA (b–d) Electron micrographs of wild-type AIM2FL filaments assembled on λdsDNA. (e–j) Electron micrographs of AIM2FL mutants bound to λdsDNA. (k) A cartoon of the AIM2PYD filament and the locations of mutated side chains based on the congruent helical symmetry between AIM2PYD and ASCPYD (see also Fig. 7b). Scale bar, 100 nm.

Mentions: A previous cell-based imaging study showed that isolated AIM2PYD and AIM2FL form filamentous aggregates, but AIM2Hin failed to form such structures34; whether dsDNA (transfected plasmid) is part of the filamentous AIM2FL aggregates is unknown. Our present study is consistent with this in vivo observation34, as dsDNA-free AIM2FL assembles into filaments via its PYD. However, in principle, the HIN200 domains of AIM2FL could bind dsDNA along its length, and thus might also generate an ordered filamentous structure. Thus, to further resolve whether AIM2PYD or AIM2Hin oligomers dictate the overall architecture of dsDNA-bound AIM2FL, we determined the morphologies of AIM2FL and AIM2Hin bound to λ-phage dsDNA (λdsDNA) using ns-EM. Isolated AIM2Hin did not show any ordered filaments, but displayed random ‘beads on a string'-like clusters on λdsDNA (Fig. 8a). By contrast, the Brussels sprout-like filaments were no longer detected on adding dsDNA to AIM2FL, but new larger filaments about two- to three-times wider than the DNA-free filaments appeared in the micrographs (20–25 nm; Fig. 8b), indicating dsDNA binding. Together, these observations suggest that AIM2Hin binds dsDNA and clusters randomly, and that AIM2PYD oligomers underpin the filamentous architecture of dsDNA-bound AIM2FL.


Assembly-driven activation of the AIM2 foreign-dsDNA sensor provides a polymerization template for downstream ASC.

Morrone SR, Matyszewski M, Yu X, Delannoy M, Egelman EH, Sohn J - Nat Commun (2015)

AIM2PYD is required to assemble filamentous structures on dsDNA.(a) An electron micrograph of AIM2Hin clusters on λdsDNA (b–d) Electron micrographs of wild-type AIM2FL filaments assembled on λdsDNA. (e–j) Electron micrographs of AIM2FL mutants bound to λdsDNA. (k) A cartoon of the AIM2PYD filament and the locations of mutated side chains based on the congruent helical symmetry between AIM2PYD and ASCPYD (see also Fig. 7b). Scale bar, 100 nm.
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Related In: Results  -  Collection

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f8: AIM2PYD is required to assemble filamentous structures on dsDNA.(a) An electron micrograph of AIM2Hin clusters on λdsDNA (b–d) Electron micrographs of wild-type AIM2FL filaments assembled on λdsDNA. (e–j) Electron micrographs of AIM2FL mutants bound to λdsDNA. (k) A cartoon of the AIM2PYD filament and the locations of mutated side chains based on the congruent helical symmetry between AIM2PYD and ASCPYD (see also Fig. 7b). Scale bar, 100 nm.
Mentions: A previous cell-based imaging study showed that isolated AIM2PYD and AIM2FL form filamentous aggregates, but AIM2Hin failed to form such structures34; whether dsDNA (transfected plasmid) is part of the filamentous AIM2FL aggregates is unknown. Our present study is consistent with this in vivo observation34, as dsDNA-free AIM2FL assembles into filaments via its PYD. However, in principle, the HIN200 domains of AIM2FL could bind dsDNA along its length, and thus might also generate an ordered filamentous structure. Thus, to further resolve whether AIM2PYD or AIM2Hin oligomers dictate the overall architecture of dsDNA-bound AIM2FL, we determined the morphologies of AIM2FL and AIM2Hin bound to λ-phage dsDNA (λdsDNA) using ns-EM. Isolated AIM2Hin did not show any ordered filaments, but displayed random ‘beads on a string'-like clusters on λdsDNA (Fig. 8a). By contrast, the Brussels sprout-like filaments were no longer detected on adding dsDNA to AIM2FL, but new larger filaments about two- to three-times wider than the DNA-free filaments appeared in the micrographs (20–25 nm; Fig. 8b), indicating dsDNA binding. Together, these observations suggest that AIM2Hin binds dsDNA and clusters randomly, and that AIM2PYD oligomers underpin the filamentous architecture of dsDNA-bound AIM2FL.

Bottom Line: The ability to oligomerize is critical for binding dsDNA, and in turn permits the size of dsDNA to regulate the assembly of the AIM2 polymers.The AIM2(PYD) oligomers define the filamentous structure, and the helical symmetry of the AIM2(PYD) filament is consistent with the filament assembled by the PYD of the downstream adaptor ASC.Our results suggest that the role of AIM2(PYD) is not autoinhibitory, but generating a structural template by coupling ligand binding and oligomerization is a key signal transduction mechanism in the AIM2 inflammasome.

View Article: PubMed Central - PubMed

Affiliation: Department of Biophysics and Biophysical Chemistry, Johns Hopkins University School of Medicine Baltimore, Maryland 21205, USA.

ABSTRACT
AIM2 recognizes foreign dsDNA and assembles into the inflammasome, a filamentous supramolecular signalling platform required to launch innate immune responses. We show here that the pyrin domain of AIM2 (AIM2(PYD)) drives both filament formation and dsDNA binding. In addition, the dsDNA-binding domain of AIM2 also oligomerizes and assists in filament formation. The ability to oligomerize is critical for binding dsDNA, and in turn permits the size of dsDNA to regulate the assembly of the AIM2 polymers. The AIM2(PYD) oligomers define the filamentous structure, and the helical symmetry of the AIM2(PYD) filament is consistent with the filament assembled by the PYD of the downstream adaptor ASC. Our results suggest that the role of AIM2(PYD) is not autoinhibitory, but generating a structural template by coupling ligand binding and oligomerization is a key signal transduction mechanism in the AIM2 inflammasome.

No MeSH data available.


Related in: MedlinePlus