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1.
Cell ; 185(13): 2370-2386.e18, 2022 06 23.
Artigo em Inglês | MEDLINE | ID: mdl-35597242

RESUMO

2',3'-cAMP is a positional isomer of the well-established second messenger 3',5'-cAMP, but little is known about the biology of this noncanonical cyclic nucleotide monophosphate (cNMP). Toll/interleukin-1 receptor (TIR) domains of nucleotide-binding leucine-rich repeat (NLR) immune receptors have the NADase function necessary but insufficient to activate plant immune responses. Here, we show that plant TIR proteins, besides being NADases, act as 2',3'-cAMP/cGMP synthetases by hydrolyzing RNA/DNA. Structural data show that a TIR domain adopts distinct oligomers with mutually exclusive NADase and synthetase activity. Mutations specifically disrupting the synthetase activity abrogate TIR-mediated cell death in Nicotiana benthamiana (Nb), supporting an important role for these cNMPs in TIR signaling. Furthermore, the Arabidopsis negative regulator of TIR-NLR signaling, NUDT7, displays 2',3'-cAMP/cGMP but not 3',5'-cAMP/cGMP phosphodiesterase activity and suppresses cell death activity of TIRs in Nb. Our study identifies a family of 2',3'-cAMP/cGMP synthetases and establishes a critical role for them in plant immune responses.


Assuntos
Proteínas de Arabidopsis , Arabidopsis , Arabidopsis/genética , Proteínas de Arabidopsis/metabolismo , Morte Celular/genética , AMP Cíclico/biossíntese , GMP Cíclico/biossíntese , Ligases/metabolismo , NAD+ Nucleosidase/metabolismo , Doenças das Plantas , Imunidade Vegetal/fisiologia , Proteínas de Plantas/metabolismo , Receptores Imunológicos/metabolismo , Receptores de Interleucina-1/metabolismo , Nicotiana/genética , Nicotiana/metabolismo
2.
Immunity ; 54(10): 2218-2230.e5, 2021 10 12.
Artigo em Inglês | MEDLINE | ID: mdl-34644557

RESUMO

The RNA sensor MDA5 recruits the signaling adaptor MAVS to initiate type I interferon signaling and downstream antiviral responses, a process that requires K63-linked polyubiquitin chains. Here, we examined the mechanisms whereby K63-polyUb chain regulate MDA5 activation. Only long unanchored K63-polyUbn (n ≥ 8) could mediate tetramerization of the caspase activation and recruitment domains of MDA5 (MDA5CARDs). Cryoelectron microscopy structures of a polyUb13-bound MDA5CARDs tetramer and a polyUb11-bound MDA5CARDs-MAVSCARD assembly revealed a tower-like formation, wherein eight Ubs tethered along the outer rim of the helical shell, bridging MDA5CARDs and MAVSCARD tetramers into proximity. ATP binding and hydrolysis promoted the stabilization of RNA-bound MDA5 prior to MAVS activation via allosteric effects on CARDs-polyUb complex. Abundant ATP prevented basal activation of apo MDA5. Our findings reveal the ordered assembly of a MDA5 signaling complex competent to recruit and activate MAVS and highlight differences with RIG-I in terms of CARD orientation and Ub sensing that suggest different abilities to induce antiviral responses.


Assuntos
Proteínas Adaptadoras de Transdução de Sinal/metabolismo , Helicase IFIH1 Induzida por Interferon/metabolismo , Transdução de Sinais/fisiologia , Proteínas Adaptadoras de Transdução de Sinal/química , Microscopia Crioeletrônica , Células HEK293 , Humanos , Imunidade Inata/fisiologia , Helicase IFIH1 Induzida por Interferon/química , Helicase IFIH1 Induzida por Interferon/ultraestrutura , Poliubiquitina/química , Poliubiquitina/metabolismo , Ligação Proteica
3.
Nature ; 632(8026): 869-876, 2024 Aug.
Artigo em Inglês | MEDLINE | ID: mdl-38866053

RESUMO

Nucleotide-binding leucine-rich repeat (NLR) proteins play a pivotal role in plant immunity by recognizing pathogen effectors1,2. Maintaining a balanced immune response is crucial, as excessive NLR expression can lead to unintended autoimmunity3,4. Unlike most NLRs, the plant NLR required for cell death 2 (NRC2) belongs to a small NLR group characterized by constitutively high expression without self-activation5. The mechanisms underlying NRC2 autoinhibition and activation are not yet understood. Here we show that Solanum lycopersicum (tomato) NRC2 (SlNRC2) forms dimers and tetramers and higher-order oligomers at elevated concentrations. Cryo-electron microscopy shows an inactive conformation of SlNRC2 in these oligomers. Dimerization and oligomerization not only stabilize the inactive state but also sequester SlNRC2 from assembling into an active form. Mutations at the dimeric or interdimeric interfaces enhance pathogen-induced cell death and immunity in Nicotiana benthamiana. The cryo-electron microscopy structures unexpectedly show inositol hexakisphosphate (IP6) or pentakisphosphate (IP5) bound to the inner surface of the C-terminal leucine-rich repeat domain of SlNRC2, as confirmed by mass spectrometry. Mutations at the inositol phosphate-binding site impair inositol phosphate binding of SlNRC2 and pathogen-induced SlNRC2-mediated cell death in N. benthamiana. Our study indicates a negative regulatory mechanism of NLR activation and suggests inositol phosphates as cofactors of NRCs.


Assuntos
Proteínas NLR , Ácido Fítico , Proteínas de Plantas , Multimerização Proteica , Solanum lycopersicum , Sítios de Ligação , Morte Celular , Microscopia Crioeletrônica , Modelos Moleculares , Mutação , Nicotiana/citologia , Nicotiana/imunologia , Nicotiana/metabolismo , Proteínas NLR/antagonistas & inibidores , Proteínas NLR/química , Proteínas NLR/genética , Proteínas NLR/metabolismo , Proteínas NLR/ultraestrutura , Ácido Fítico/metabolismo , Ácido Fítico/química , Imunidade Vegetal , Proteínas de Plantas/antagonistas & inibidores , Proteínas de Plantas/química , Proteínas de Plantas/genética , Proteínas de Plantas/metabolismo , Proteínas de Plantas/ultraestrutura , Ligação Proteica , Domínios Proteicos , Solanum lycopersicum/citologia , Solanum lycopersicum/genética , Solanum lycopersicum/imunologia , Solanum lycopersicum/metabolismo
4.
Nat Commun ; 12(1): 188, 2021 01 08.
Artigo em Inglês | MEDLINE | ID: mdl-33420028

RESUMO

Nod-like receptor (NLR) proteins activate pyroptotic cell death and IL-1 driven inflammation by assembling and activating the inflammasome complex. Closely related sensor proteins NLRP1 and CARD8 undergo unique auto-proteolysis-dependent activation and are implicated in auto-inflammatory diseases; however, their mechanisms of activation are not understood. Here we report the structural basis of how the activating domains (FIINDUPA-CARD) of NLRP1 and CARD8 self-oligomerize to assemble distinct inflammasome complexes. Recombinant FIINDUPA-CARD of NLRP1 forms a two-layered filament, with an inner core of oligomerized CARD surrounded by an outer ring of FIINDUPA. Biochemically, self-assembled NLRP1-CARD filaments are sufficient to drive ASC speck formation in cultured human cells-a process that is greatly enhanced by NLRP1-FIINDUPA which forms oligomers in vitro. The cryo-EM structures of NLRP1-CARD and CARD8-CARD filaments, solved here at 3.7 Å, uncover unique structural features that enable NLRP1 and CARD8 to discriminate between ASC and pro-caspase-1. In summary, our findings provide structural insight into the mechanisms of activation for human NLRP1 and CARD8 and reveal how highly specific signaling can be achieved by heterotypic CARD interactions within the inflammasome complexes.


Assuntos
Proteínas Adaptadoras de Transdução de Sinal/metabolismo , Proteínas Reguladoras de Apoptose/metabolismo , Proteínas Adaptadoras de Sinalização CARD/metabolismo , Inflamassomos/química , Inflamassomos/metabolismo , Proteínas de Neoplasias/metabolismo , Proteínas Adaptadoras de Transdução de Sinal/química , Proteínas Adaptadoras de Transdução de Sinal/genética , Proteínas Reguladoras de Apoptose/química , Proteínas Reguladoras de Apoptose/genética , Proteínas Adaptadoras de Sinalização CARD/genética , Caspase 1/metabolismo , Microscopia Crioeletrônica , Células HEK293 , Humanos , Inflamassomos/genética , Inflamação , Simulação de Acoplamento Molecular , Mutação , Proteínas NLR , Proteínas de Neoplasias/química , Proteínas de Neoplasias/genética , Transdução de Sinais
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