NLRX1 (NLR family member X1; also known as NOD5/NOD9 and CLR11.3) is an atypical nucleotide-binding-domain and leucine-rich-repeat-containing (NOD-like) receptor that, unusually for an NLR, localizes to the mitochondrion. An N-terminal mitochondrial transit peptide targets it to the mitochondrial outer membrane, it has a central NACHT NTPase domain, and a C-terminal leucine-rich-repeat region that carries an RNA-binding element; the protein assembles into a homohexamer. NLRX1 functions as a mitochondrial regulator at the intersection of antiviral innate immunity, autophagy, reactive oxygen species and inflammasome control. Its best-characterized role is as a negative regulator of MAVS-mediated (RIG-I-like helicase) antiviral signaling: by interacting with MAVS at the mitochondrial outer membrane it disrupts the virus-induced RIG-I-MAVS interaction and dampens type I interferon production, so that its depletion enhances antiviral interferon responses and reduces viral replication. NLRX1 also promotes autophagy by binding the mitochondrial elongation factor TUFM, which recruits the autophagy machinery (ATG5-ATG12, ATG16L1), linking it to autophagy/mitophagy and to modulation of type I interferon. It additionally restrains MAVS-dependent NLRP3 inflammasome activation, limiting IL-1beta/ IL-18 production and apoptosis, and it modulates reactive oxygen species production with downstream effects on NF-kappaB and JNK signaling. Through these activities NLRX1 acts as a mitochondrial checkpoint that tunes the strength of antiviral, inflammatory and autophagic responses.
Definition: Any process that activates or increases the frequency, rate or extent of autophagy.
Justification: NLRX1's TUFM-dependent recruitment of ATG5-ATG12 to promote autophagy (PMID:22749352) is documented in UniProt FUNCTION but is not represented in the current GOA. A positive regulation of autophagy (GO:0010508) annotation - and potentially a regulation-of-mitophagy annotation - would capture this established core function.
Parent term: positive regulation of autophagy
Supporting Evidence:
| GO Term | Evidence | Action | Reason |
|---|---|---|---|
| GO:0039536 negative regulation of RIG-I signaling pathway | IBA GO_REF:0000033 | ACCEPT | Summary: Phylogenetic (IBA) assignment of negative regulation of RIG-I signaling, strongly corroborated by experimental evidence that NLRX1 disrupts the virus-induced RIG-I-like-helicase-MAVS interaction and dampens type I IFN. Core function. Recent review-level synthesis (falcon) frames this as the founding NLRX1 function but cautions the effect is context-/cell-type-dependent rather than universally inhibitory. Reason: Core biological process; NLRX1 negatively regulates the RIG-I/MAVS antiviral pathway (experimentally supported by PMID:18200010). The direction (negative regulation) is consistent across the foundational experimental papers and recent reviews, though the magnitude is reported to depend on cell type and pathogen. Supporting Evidence: PMID:18200010 disruption of virus-induced RLH-MAVS interactions file:human/NLRX1/NLRX1-deep-research-falcon.md NLRX1 sequesters MAVS and prevents RIG-I/MAVS association, thereby reducing type I interferon and NF-ΞΊB responses to RNA viruses file:human/NLRX1/NLRX1-deep-research-falcon.md function appears context dependent rather than universally inhibitory |
| GO:0005739 mitochondrion | IBA GO_REF:0000033 | ACCEPT | Summary: Phylogenetic (IBA) assignment of mitochondrial localization, the defining and experimentally established compartment for NLRX1 (mitochondrial outer membrane via its N-terminal transit peptide). The general "mitochondrion" term is appropriately robust to the ongoing debate over sub-compartment - recent review-level synthesis (falcon) additionally places NLRX1 in the matrix and inner mitochondrial membrane, though these sub-compartmental claims rest on uncached recent work and are not independently verified here. Reason: Core localization; NLRX1 is a mitochondrial NLR. The broad mitochondrion term is well supported regardless of which mitochondrial sub-compartment dominates. Supporting Evidence: PMID:18200010 localizes to the mitochondrial outer membrane and interacts with MAVS file:human/NLRX1/NLRX1-deep-research-falcon.md NLRX1 is the only NLR family member to localize to mitochondria |
| GO:0043124 negative regulation of canonical NF-kappaB signal transduction | IBA GO_REF:0000033 | MARK AS OVER ANNOTATED | Summary: Phylogenetic (IBA) assignment of negative regulation of canonical NF-kappaB, transferred from the mouse ortholog. This direction is genuinely contested - UniProt and the human primary paper PMID:18219313 state NLRX1 has NO inhibitory function on NF-kappaB and instead ENHANCES NF-kappaB and JNK signaling via ROS production, whereas other studies (and recent review-level synthesis captured in falcon) report a negative regulatory role acting through TRAF6/IKK. The literature is unresolved. Reason: The NF-kappaB role of NLRX1 is genuinely disputed in the literature. The human-specific primary study (PMID:18219313) reports NLRX1 amplifies (not inhibits) NF-kappaB via ROS, while review-level sources continue to describe NLRX1 as a negative regulator of NF-kappaB (e.g. via TRAF6 and IKK). Because the direction is unresolved for human NLRX1, this unverified phylogenetic (IBA) inference of a strictly negative role is best treated as an over-annotation rather than accepted at face value or removed outright; the mouse-ortholog/review evidence underlying the IBA is real. Supporting Evidence: file:human/NLRX1/NLRX1-uniprot.txt Has no inhibitory function on NF-kappa-B signaling pathway, but enhances NF-kappa-B and JUN N-terminal kinase dependent signaling through the production of reactive oxygen species file:human/NLRX1/NLRX1-deep-research-falcon.md NLRX1 negatively regulates NF-ΞΊB activation through multiple mechanisms, including binding to TRAF6 (tumor necrosis factor receptor-associated factor 6) to prevent downstream TLR signaling, and interacting with IKK (IΞΊB kinase) to prevent IΞΊB phosphorylation |
| GO:0005741 mitochondrial outer membrane | IEA GO_REF:0000044 | ACCEPT | Summary: Electronic transfer of mitochondrial outer membrane localization from the UniProt subcellular location, redundant with the experimental EXP/TAS annotations. Core localization. Reason: Core localization; NLRX1 resides at the mitochondrial outer membrane. Supporting Evidence: file:human/NLRX1/NLRX1-uniprot.txt SUBCELLULAR LOCATION: Mitochondrion outer membrane |
| GO:0005515 protein binding | IPI PMID:21903422 Mapping a dynamic innate immunity protein interaction networ... | KEEP AS NON CORE | Summary: IPI interaction (SARM1, a xeno/mouse partner) from a dynamic innate-immunity interaction network. Bare protein binding is uninformative. Reason: High-throughput innate-immunity interactome; bare protein binding is uninformative. Supporting Evidence: file:human/NLRX1/NLRX1-uniprot.txt Q86UT6; Q6PDS3: Sarm1; Xeno; NbExp=2; IntAct=EBI-3893071, EBI-6117196 |
| GO:0005515 protein binding | IPI PMID:28611246 Inhibition of Avian Influenza A Virus Replication in Human C... | KEEP AS NON CORE | Summary: IPI interaction with TUFM (P49411) from a study of TUFM as a host restriction factor against avian influenza correlated with autophagy. The NLRX1-TUFM interaction is functionally central (it recruits ATG5-ATG12 to drive autophagy), but bare protein binding is uninformative. Reason: Records the functionally important NLRX1-TUFM interaction that underpins NLRX1's autophagy-promoting role, but bare protein binding is uninformative; the autophagy function is the informative annotation. Supporting Evidence: file:human/NLRX1/NLRX1-uniprot.txt Q86UT6; P49411: TUFM; NbExp=2; IntAct=EBI-3893071, EBI-359097 |
| GO:0005739 mitochondrion | IDA GO_REF:0000052 | ACCEPT | Summary: HPA immunofluorescence localization to the mitochondrion, consistent with NLRX1's established mitochondrial localization. Core compartment. Reason: Core localization; NLRX1 is a mitochondrial NLR. Supporting Evidence: file:human/NLRX1/NLRX1-uniprot.txt SUBCELLULAR LOCATION: Mitochondrion outer membrane |
| GO:0005741 mitochondrial outer membrane | EXP PMID:18200010 NLRX1 is a regulator of mitochondrial antiviral immunity. | ACCEPT | Summary: Experimental evidence that NLRX1 localizes to the mitochondrial outer membrane, where it interacts with MAVS. Core localization establishing the basis of its MAVS regulation. Reason: Core localization with direct experimental support; the mitochondrial outer membrane is where NLRX1 engages MAVS. Supporting Evidence: PMID:18200010 localizes to the mitochondrial outer membrane and interacts with MAVS |
| GO:0005741 mitochondrial outer membrane | EXP PMID:27393910 NLRX1 attenuates apoptosis and inflammatory responses in myo... | ACCEPT | Summary: Experimental evidence (myocardial ischemia study) that NLRX1 localizes to mitochondria, where it regulates MAVS-dependent NLRP3 inflammasome activation. Core localization. Reason: Core localization with experimental support. Supporting Evidence: PMID:27393910 NLRX1, located in mitochondria |
| GO:0005739 mitochondrion | HTP PMID:34800366 Quantitative high-confidence human mitochondrial proteome an... | ACCEPT | Summary: High-throughput proteomic evidence (human mitochondrial proteome) placing NLRX1 in the mitochondrion, consistent with all other evidence. Core compartment. Reason: Core localization; corroborates the experimental mitochondrial localization. Supporting Evidence: file:human/NLRX1/NLRX1-uniprot.txt SUBCELLULAR LOCATION: Mitochondrion outer membrane |
| GO:0005829 cytosol | TAS Reactome:R-HSA-9749471 | MARK AS OVER ANNOTATED | Summary: Reactome pathway-step curation (NLRX1 binds CHUK:IKBKB:IKBKG) placing NLRX1 in the cytosol. NLRX1's dominant, experimentally established localization is the mitochondrial outer membrane. Reason: Derived from a single Reactome pathway model of an IKK interaction; conflicts with the strongly supported mitochondrial outer membrane localization and is not the core compartment for NLRX1. Supporting Evidence: file:human/NLRX1/NLRX1-uniprot.txt SUBCELLULAR LOCATION: Mitochondrion outer membrane |
| GO:0005741 mitochondrial outer membrane | TAS Reactome:R-HSA-936564 | ACCEPT | Summary: Reactome curation (NLRX1 inhibits MAVS-DDX58 interaction) placing NLRX1 at the mitochondrial outer membrane, consistent with the experimental localization and its MAVS-regulatory function. Core localization. Reason: Core localization; matches the experimental mitochondrial outer membrane evidence and the MAVS-regulation function. Supporting Evidence: PMID:18200010 localizes to the mitochondrial outer membrane and interacts with MAVS |
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Download this section (compressed HTML)Q: Is the negative-regulation-of-NF-kappaB role assigned by phylogenetic inference (IBA, from the mouse ortholog) correct for human NLRX1, given that human studies report NLRX1 amplifies NF-kappaB/JNK via ROS rather than inhibiting it?
Q: How does NLRX1 partition between its MAVS-inhibitory (antiviral-dampening) role and its TUFM-dependent autophagy-promoting role - are these mutually exclusive complexes, and how are they triggered during infection?
Q: Does human NLRX1 act as a direct mitophagy receptor via LC3 binding (as proposed in recent reviews and an acetyl-CoA-sensing model), or is its autophagy role indirect via the TUFM/ATG5-ATG12 axis as shown in the foundational study (PMID:22749352), which did not detect mitophagy under its conditions?
Experiment: Define the endogenous NLRX1 mitochondrial interactome (MAVS versus TUFM/ATG5-ATG12) under resting versus viral-infection conditions by proximity labeling to test whether the MAVS-inhibitory and autophagy-promoting complexes are temporally or spatially separated.
Experiment: Test the human NF-kappaB direction directly with NLRX1 knockout/reconstitution plus ROS scavengers and NF-kappaB/JNK reporters to resolve whether human NLRX1 enhances or inhibits canonical NF-kappaB, adjudicating the disputed IBA annotation.
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