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-κB 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-κB activation through multiple mechanisms, including binding to TRAF6 (tumor necrosis factor receptor-associated factor 6) to prevent downstream TLR signaling, and interacting with IKK (IκB kinase) to prevent IκB 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
|
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.
The research report should be a detailed narrative explaining the function, biological processes, and localization of the gene product. Citations should be given for all claims.
You should prioritize authoritative reviews and primary scientific literature when conducting research. You can supplement
this with annotations you find in gene/protein databases, but these can be outdated or inaccurate.
We are specifically interested in the primary function of the gene - for enzymes, what reaction is catalyzed, and what is the substrate specificity? For transporters, what is the substrate? For structural proteins or adapters, what is the broader structural role? For signaling molecules, what is the role in the pathway.
We are interested in where in or outside the cell the gene product carries out its function.
We are also interested in the signaling or biochemical pathways in which the gene functions. We are less interested in broad pleiotropic effects, except where these elucidate the precise role.
Include evidence where possible. We are interested in both experimental evidence as well as inference from structure, evolution, or bioinformatic analysis. Precise studies should be prioritized over high-throughput, where available.
Gene: NLRX1
UniProt Accession: Q86UT6
Synonyms: NOD5, NOD9, CLR11.3
Organism: Homo sapiens (Human)
Protein Family: NLRP family (NLR superfamily)
NLRX1 (NLR family member X1) is a unique member of the nucleotide-binding domain and leucine-rich repeat (NLR) protein family that distinguishes itself from other NLRs through its mitochondrial localization (bi2024nlrx1versatilefunctions pages 1-2, pickering2021nlrinexile pages 1-4). Unlike typical NLRs that function in the cytoplasm, NLRX1 is the only NLR family member to localize to mitochondria, making it an atypical pattern recognition receptor with specialized regulatory functions (bi2024nlrx1versatilefunctions pages 1-2, pickering2021nlrinexile pages 1-4, chou2023thenlrgene pages 1-3). The protein belongs to the NLRP family and contains characteristic domains including a central NACHT (nucleotide-binding and oligomerization) domain, C-terminal leucine-rich repeats (LRR), and a unique N-terminal region housing a mitochondrial targeting sequence (bi2024nlrx1versatilefunctions pages 1-2, pickering2021nlrinexile pages 1-4, fekete2021focusingonthe pages 1-2).
NLRX1 possesses a modular domain organization consisting of three main regions (pickering2021nlrinexile pages 1-4, chou2023thenlrgene pages 1-3):
N-terminal region (amino acids 1-39): Contains a functional mitochondrial targeting sequence (MTS) that directs the nascent protein to mitochondria. This sequence is cleaved by mitochondrial matrix proteases upon import, yielding the mature protein (bi2024nlrx1versatilefunctions pages 1-2, bi2024nlrx1versatilefunctions pages 2-3).
NACHT domain (central region): This nucleotide-binding and oligomerization domain is responsible for ATPase activity and protein-protein interactions. Recent structural studies using AlphaFold2 modeling have revealed that NLRX1 can form stable centrosymmetric hexameric structures, a characteristic feature of AAA+ (ATPase Associated with Diverse Cellular Activity) family proteins (jewell2024insightsintothe pages 1-2).
Leucine-rich repeat (LRR) domain (C-terminal, residues 629-975): The LRR domain has been crystallized (PDB: 3UN9) and serves multiple functions including ligand binding, protein interactions, and metabolite sensing. Recent breakthrough studies identified binding pockets for RNA and acetyl-coenzyme A (AcCoA) within the LRR domain, revealing novel regulatory mechanisms (jewell2024insightsintothe pages 1-2, zhang2026cytosolicacetylcoenzymea pages 1-2).
Advanced structural analyses published in 2024 demonstrate that the LRR domain maintains NLRX1 in an autoinhibited state through interactions with the NACHT domain. Binding of cytosolic AcCoA to a conserved pocket on the LRR domain enhances this interaction, preventing NLRX1 from associating with LC3 and thus regulating mitophagy initiation (zhang2026cytosolicacetylcoenzymea pages 1-2). This represents an elegant metabolic sensing mechanism linking cellular energy status to mitochondrial quality control.
NLRX1 executes its diverse functions from multiple locations within mitochondria:
Mitochondrial Matrix: Following import through the TOM (translocase of outer membrane) and TIM (translocase of inner membrane) complexes, mature NLRX1 localizes to the mitochondrial matrix where it interacts with UQCRC2, a matrix-facing component of respiratory chain complex III (bi2024nlrx1versatilefunctions pages 1-2, bi2024nlrx1versatilefunctions pages 2-3). In this location, NLRX1 influences reactive oxygen species (ROS) generation and mitochondrial metabolism.
Inner Mitochondrial Membrane: Groundbreaking research published in 2025 definitively localized NLRX1 to the inner mitochondrial membrane using mitochondrial sub-fractionation studies (xiao2025theinnateimmune pages 2-5, xiao2025theinnateimmune pages 5-7). At this location, NLRX1 plays a critical role in regulating the mitochondrial permeability transition pore (mPTP), demonstrating that NLRX1 is required for calcium-induced mPTP opening (xiao2025theinnateimmune pages 5-7).
Outer Mitochondrial Membrane: Recent evidence also places NLRX1 on the outer mitochondrial membrane, particularly in its capacity as a mitophagy receptor. In this location, NLRX1 can directly interact with cytosolic LC3 to initiate selective mitochondrial autophagy (bi2024nlrx1versatilefunctions pages 1-2, zhang2026cytosolicacetylcoenzymea pages 1-2).
This dynamic multi-compartmental localization enables NLRX1 to integrate signals from different mitochondrial microenvironments and coordinate complex cellular responses.
A central and increasingly recognized function of NLRX1 is its role as a mitophagy receptor that mediates selective removal of damaged mitochondria (bi2024nlrx1versatilefunctions pages 1-2, zhang2026cytosolicacetylcoenzymea pages 1-2). NLRX1 directly binds to LC3 (microtubule-associated protein 1 light chain 3), the key autophagosome marker, to facilitate mitochondrial engulfment. This function has been demonstrated across multiple tissue types and disease models, with 2024 studies proposing that mitophagy regulation may represent the overarching unifying function of NLRX1 (bi2024nlrx1versatilefunctions pages 1-2).
Mechanism: NLRX1 detects mitochondrial protein import stress (MPIS) as a "danger signal" indicating mitochondrial dysfunction. Upon sensing MPIS, NLRX1 promotes LC3 lipidation and recruitment to mitochondria, initiating the mitophagic cascade (bi2024nlrx1versatilefunctions pages 1-2). Recent work in 2026 revealed that cytosolic acetyl-CoA acts as a signaling metabolite: when AcCoA levels decrease (as during fasting), NLRX1's autoinhibition is relieved, allowing LC3 binding and mitophagy induction (zhang2026cytosolicacetylcoenzymea pages 1-2).
NLRX1 functions as a negative regulator of multiple innate immune pathways, dampening inflammatory and antiviral responses:
RIG-I/MAVS Pathway: NLRX1 was initially characterized for its interaction with MAVS (mitochondrial antiviral signaling protein), an adaptor for RIG-I-like receptors (RLRs) that detect viral RNA. NLRX1 sequesters MAVS and prevents RIG-I/MAVS association, thereby reducing type I interferon and NF-κB responses to RNA viruses (bi2024nlrx1versatilefunctions pages 2-3). NLRX1 also activates poly(rC) binding protein 2 (PCBP2) to facilitate proteasomal degradation of MAVS, further suppressing antiviral signaling (bi2024nlrx1versatilefunctions pages 2-3). However, recent literature notes context-dependent effects, with some studies showing that NLRX1 effects on antiviral immunity vary by cell type and specific pathogen (bi2024nlrx1versatilefunctions pages 1-2, pickering2021nlrinexile pages 1-4).
cGAS-STING Pathway: Similar to its effects on MAVS, NLRX1 has been proposed to inhibit the cGAS-STING DNA sensing pathway by preventing STING-TBK1 association, thus limiting type I interferon production in response to cytosolic DNA or mitochondrial DNA (mtDNA) leakage (bi2024nlrx1versatilefunctions pages 2-3, pickering2021nlrinexile pages 1-4).
NF-κB Signaling: NLRX1 negatively regulates NF-κB activation through multiple mechanisms, including binding to TRAF6 (tumor necrosis factor receptor-associated factor 6) to prevent downstream TLR signaling, and interacting with IKK (IκB kinase) to prevent IκB phosphorylation (jewell2024insightsintothe pages 1-2, bi2024nlrx1versatilefunctions pages 2-3). This positions NLRX1 as a key suppressor of inflammatory gene transcription.
NLRX1 plays multifaceted roles in cellular metabolism, functioning as a metabolic checkpoint that coordinates energy production with cellular homeostasis:
OXPHOS Regulation: Through its interaction with FASTKD5 (Fas-activated serine-threonine kinase family protein-5) in the mitochondrial matrix, NLRX1 regulates mitochondrial transcript processing, respiratory complex expression, and oxidative phosphorylation (OXPHOS) activity (chou2022impactofintracellular pages 7-8). The NLRX1-FASTKD5 complex modulates complexes I and IV of the electron transport chain and influences mitochondrial ribosome biogenesis (chou2022impactofintracellular pages 7-8). In human CD4+ T cells infected with HIV-1, this interaction enhances OXPHOS to support viral replication, demonstrating clinically relevant metabolic control (chou2022impactofintracellular pages 7-8).
Glycolysis and Fatty Acid Metabolism: NLRX1 deficiency leads to altered metabolic programming. Studies show that Nlrx1−/− mice are protected against high-fat diet-induced metabolic syndrome and nonalcoholic fatty liver disease (NAFLD), with increased fatty acid oxidation (FAO) and decreased hepatic steatosis (chou2022impactofintracellular pages 7-8). NLRX1 normally restricts mitochondrial fatty acid-dependent OXPHOS while enhancing glycolysis in hepatocytes (chou2022impactofintracellular pages 7-8).
mTOR/AMPK Balance: NLRX1 intersects with major metabolic signaling pathways. In cardiac ischemia-reperfusion models, NLRX1 facilitates mTOR and RISK (reperfusion injury salvage kinase) pathway activation, including phosphorylation of Akt, ERK, and S6K (xiao2025theinnateimmune pages 5-7). NLRX1 deletion is associated with compensatory AMPK activation, linking NLRX1 to the cellular energy-sensing machinery (xiao2025theinnateimmune pages 5-7, chou2022impactofintracellular pages 7-8).
Beyond mitophagy, NLRX1 orchestrates mitochondrial dynamics through novel mechanisms:
NLRX1-SLC39A7 Complex: A 2024 study revealed that NLRX1 forms a complex with the zinc transporter SLC39A7 (ZIP7) on mitochondrial membranes to modulate mitochondrial Zn²⁺ trafficking (song2024thenlrx1slc39a7complex pages 1-2). This complex coordinates mitochondrial fission (via DNM1L/DRP1 phosphorylation and OMA1 activity) with fusion (via L-OPA1:S-OPA1 ratio) and synchronizes these dynamic processes with mitophagy activity. Loss of NLRX1 causes mitochondrial fragmentation and triggers excessive compensatory PINK1-PRKN-mediated mitophagy, leading to cellular senescence (song2024thenlrx1slc39a7complex pages 1-2).
mPTP Regulation: Groundbreaking 2025 research established NLRX1 as a novel required modulator of mPTP opening (xiao2025theinnateimmune pages 2-5, xiao2025theinnateimmune pages 5-7). Using calcium retention capacity assays and mitochondrial sub-fractionation, investigators showed that NLRX1 deletion completely abolished calcium-induced mPTP opening and altered mitochondrial calcium handling. This function links NLRX1 to cardioprotection during ischemia-reperfusion injury (xiao2025theinnateimmune pages 5-7).
NLRX1 participates in multiple interconnected signaling networks. A comprehensive summary is provided in the following table:
| Pathway/Process | Molecular Partners/Targets | Mechanism of Action | Functional Outcome |
|---|---|---|---|
| RIG-I/MAVS antiviral signaling | MAVS, RIG-I, MDA5, PCBP2 | NLRX1 has been reported to associate with MAVS and interfere with RIG-I/MAVS complex formation; it can also promote PCBP2-dependent proteasomal degradation of MAVS. These effects generally dampen downstream IRF3/NF-κB signaling, although some studies note context- and cell-type-dependent disagreement. (bi2024nlrx1versatilefunctions pages 2-3, pickering2021nlrinexile pages 1-4) | Usually decreases type I interferon and antiviral inflammatory responses to RNA viruses; function appears context dependent rather than universally inhibitory. (bi2024nlrx1versatilefunctions pages 2-3, pickering2021nlrinexile pages 1-4) |
| cGAS-STING DNA sensing | STING, TBK1, cGAS | NLRX1 has been proposed to sequester STING or limit STING-TBK1 association, analogous to its reported effects on MAVS-dependent signaling; recent injury and viral-infection literature continues to place NLRX1 upstream of cGAS-STING regulation. (bi2024nlrx1versatilefunctions pages 2-3, pickering2021nlrinexile pages 1-4) | Typically restrains type I interferon production and inflammatory signaling in response to cytosolic DNA or mtDNA leakage. (bi2024nlrx1versatilefunctions pages 2-3, pickering2021nlrinexile pages 1-4) |
| NF-κB inflammation | TRAF6, IKK, IκB, NF-κB | Structural/drug-discovery work and prior functional studies indicate that NLRX1 negatively regulates NF-κB signaling, including through interactions that prevent IKK-mediated IκB phosphorylation and through TRAF6-associated suppression of inflammatory signaling. (jewell2024insightsintothe pages 1-2, bi2024nlrx1versatilefunctions pages 2-3) | Reduced transcription of pro-inflammatory genes and dampened inflammatory signaling; relevant to inflammatory disease targeting. (jewell2024insightsintothe pages 1-2, pickering2021nlrinexile pages 1-4) |
| mTOR/AMPK metabolism | mTOR, RISK kinases (Akt, ERK, S6K), AMPK | NLRX1 influences the balance between anabolic and stress-response signaling. In cardiac ischemia-reperfusion models, NLRX1 supports mTOR and RISK pathway activation, while NLRX1 deficiency is associated with compensatory AMPK activation; other immunometabolic studies link NLRX1 to altered OXPHOS/glycolysis and fatty acid metabolism. (xiao2025theinnateimmune pages 5-7, chou2022impactofintracellular pages 7-8) | Coordinates metabolic adaptation, stress responses, and tissue protection; effects are tissue-specific and can alter susceptibility to ischemic or inflammatory injury. (xiao2025theinnateimmune pages 5-7, chou2022impactofintracellular pages 7-8) |
| Mitophagy receptor function | LC3, LC3 lipidation machinery, mitochondrial import-stress signals | Recent work positions NLRX1 as a mitophagy regulator/receptor. It promotes selective mitochondrial clearance by engaging LC3-related autophagy machinery, and broader literature frames mitophagy control as a core unifying NLRX1 function. (bi2024nlrx1versatilefunctions pages 1-2, zhang2026cytosolicacetylcoenzymea pages 1-2) | Maintains mitochondrial quality control by promoting removal of damaged mitochondria, thereby limiting secondary inflammatory and metabolic dysfunction. (bi2024nlrx1versatilefunctions pages 1-2, zhang2026cytosolicacetylcoenzymea pages 1-2) |
| Mitochondrial dynamics / Zn2+ trafficking | SLC39A7/ZIP7, DNM1L/DRP1, OPA1, OMA1, PINK1-PRKN | In nucleus pulposus cells, NLRX1 forms an NLRX1-SLC39A7 complex on mitochondrial membranes and regulates mitochondrial Zn2+ trafficking, coordinating fission/fusion factors with mitophagy. Loss of NLRX1 causes mitochondrial collapse and compensatory PINK1-PRKN pathway activation. (song2024thenlrx1slc39a7complex pages 1-2) | Preserves balanced mitochondrial dynamics and beneficial mitophagy, preventing senescence-associated mitochondrial failure and inflammatory degeneration. (song2024thenlrx1slc39a7complex pages 1-2) |
| OXPHOS regulation / mitochondrial gene expression | FASTKD5, mitochondrial RNA granules, respiratory complexes I and IV, UQCRC2 | NLRX1 associates with FASTKD5 in the mitochondrial matrix, influencing mitochondrial transcript processing, respiratory-complex expression, ribosome biogenesis/translation, and OXPHOS output. NLRX1 also interacts with UQCRC2, linking it to respiratory-chain function and ROS regulation. (chou2022impactofintracellular pages 7-8, bi2024nlrx1versatilefunctions pages 2-3) | Alters oxidative phosphorylation, glycolysis coupling, and mitochondrial bioenergetics in immune and nonimmune cells; can support virus-associated or tissue-specific metabolic programs. (chou2022impactofintracellular pages 7-8, bi2024nlrx1versatilefunctions pages 2-3) |
| mPTP regulation | mPTP, mitochondrial calcium handling machinery, phosphoproteins in inner mitochondrial membrane | In a 2025 cardiac study, NLRX1 was localized to the inner mitochondrial membrane and found to be required for calcium-induced mPTP opening; deletion abolished mPTP opening and altered mitochondrial calcium retention and phosphoprotein states. (xiao2025theinnateimmune pages 2-5, xiao2025theinnateimmune pages 5-7) | NLRX1 modulates mitochondrial permeability transition and cardioprotective signaling during ischemia-reperfusion, linking innate immune sensing to acute mitochondrial stress responses. (xiao2025theinnateimmune pages 2-5, xiao2025theinnateimmune pages 5-7) |
Table: This table summarizes the main signaling pathways and biochemical functions currently attributed to human NLRX1 from recent and foundational literature. It is useful for functional annotation because it links each pathway to specific molecular partners, mechanistic evidence, and biological outcomes.
The pathways detailed above demonstrate NLRX1's role as a central regulatory hub that integrates mitochondrial function with innate immunity, metabolism, and cellular stress responses.
Localization Studies: Mitochondrial localization of NLRX1 has been rigorously demonstrated using immunogold electron microscopy, cellular fractionation, and immunofluorescence co-localization with mitochondrial markers (TOMM20, CYTB, HSP60) (bi2024nlrx1versatilefunctions pages 1-2, bi2024nlrx1versatilefunctions pages 2-3, xiao2025theinnateimmune pages 5-7). The 2025 cardiac study employed mitochondrial sub-fractionation to definitively place NLRX1 at the inner mitochondrial membrane (xiao2025theinnateimmune pages 5-7).
Functional Assays: Mitophagy has been assessed using multiple complementary approaches including mt-Keima fluorescence (pH-sensitive mitochondrial reporter), LC3 puncta formation and co-localization with mitochondria, mitochondrial DNA/nuclear DNA ratio measurements, and transmission electron microscopy visualization of mitochondria within autophagosomes (bi2024nlrx1versatilefunctions pages 1-2, zhang2026cytosolicacetylcoenzymea pages 1-2).
Interaction Studies: Co-immunoprecipitation followed by mass spectrometry has identified key NLRX1 binding partners including FASTKD5, SLC39A7, UQCRC2, MAVS, and mTOR complex components (song2024thenlrx1slc39a7complex pages 1-2, xiao2025theinnateimmune pages 5-7, chou2022impactofintracellular pages 7-8).
In Vivo Models: NLRX1 function has been examined in multiple knockout mouse models across diverse disease contexts including: experimental autoimmune encephalomyelitis (multiple sclerosis model), cardiac ischemia-reperfusion injury, intervertebral disc degeneration, viral infections, and metabolic syndrome (song2024thenlrx1slc39a7complex pages 1-2, xiao2025theinnateimmune pages 5-7, pickering2021nlrinexile pages 9-11, chou2022impactofintracellular pages 7-8). Additionally, pig models of cardiac injury have confirmed NLRX1 downregulation following ischemia-reperfusion (xiao2025theinnateimmune pages 5-7).
Crystallography: The C-terminal LRR domain of NLRX1 (residues 629-975) has been crystallized and its structure deposited in the Protein Data Bank (PDB: 3UN9) (jewell2024insightsintothe pages 1-2). This structure has been essential for understanding ligand binding and protein-protein interactions.
AlphaFold2 Modeling: Full-length NLRX1 has been modeled using AlphaFold2, revealing a stable centrosymmetric homo-hexameric structure characteristic of AAA+ ATPases (jewell2024insightsintothe pages 1-2). These models have identified previously uncharacterized features including an RNA-binding pocket formed by N-terminal helices surrounding the hexamer center, and the acetyl-CoA binding site in the LRR domain (jewell2024insightsintothe pages 1-2, zhang2026cytosolicacetylcoenzymea pages 1-2).
Mutagenesis Studies: Domain mapping experiments have identified functional regions: the LRR domain is required for MAVS and STING interactions, metabolite binding, and IKK inhibition; the NACHT domain mediates ATPase activity and oligomerization; and the N-terminal region (beyond the MTS) contains the newly discovered RNA-binding pocket (jewell2024insightsintothe pages 1-2).
NLRX1 has emerged as a potential therapeutic target in multiple disease contexts:
Neuroinflammatory Diseases: NLRX1 protects against experimental autoimmune encephalomyelitis (EAE), a model of multiple sclerosis. Nlrx1−/− mice exhibit worse clinical outcomes with increased T cell infiltration and microglial activation (pickering2021nlrinexile pages 9-11). Rare NLRX1 mutations (including p.Glu192Ter truncation) have been identified in MS patients, linking genetic variants to disease susceptibility (pickering2021nlrinexile pages 1-4, pickering2021nlrinexile pages 9-11).
Cardiovascular Disease: NLRX1 provides cardioprotection during ischemia-reperfusion injury through mTOR/RISK pathway activation and mPTP regulation. NLRX1 deletion increases infarct size and cardiac dysfunction in mouse models (xiao2025theinnateimmune pages 5-7).
Metabolic Disorders: NLRX1 deficiency protects against diet-induced metabolic syndrome, NAFLD, and pancreatic dysfunction, suggesting NLRX1 inhibition could be therapeutic for metabolic disease (chou2022impactofintracellular pages 7-8).
Intervertebral Disc Degeneration: Loss of NLRX1 correlates with disc degeneration and cellular senescence. Restoration of NLRX1 function using genetic overexpression or the pharmacological agonist NX-13 shows therapeutic potential (song2024thenlrx1slc39a7complex pages 1-2).
Recent advances have substantially refined our understanding of NLRX1:
Unified Mitophagy Model (2024): The 2024 review by Bi et al. proposes that mitophagy regulation represents the overarching, unifying function of NLRX1, with other roles (immune regulation, metabolism) serving this primary quality control function (bi2024nlrx1versatilefunctions pages 1-2).
Metabolite Sensing (2026): The discovery that cytosolic AcCoA directly binds NLRX1 to control mitophagy represents a paradigm shift, establishing NLRX1 as a bona fide metabolic sensor linking nutritional status to mitochondrial homeostasis (zhang2026cytosolicacetylcoenzymea pages 1-2).
mPTP Regulation (2025): The identification of NLRX1 as essential for mPTP function opens new avenues for understanding cardioprotection and mitochondrial physiology (xiao2025theinnateimmune pages 5-7).
Therapeutic Development: Small molecule NLRX1 agonists (NX-13, NX-64-3) are in preclinical/clinical development for inflammatory and degenerative diseases (jewell2024insightsintothe pages 1-2, song2024thenlrx1slc39a7complex pages 1-2).
NLRX1 (UniProt Q86UT6) is a multifunctional regulatory protein that serves as a critical nexus linking mitochondrial function, innate immunity, and cellular metabolism. Its unique mitochondrial localization enables it to function as a sentinel for mitochondrial health, coordinating appropriate cellular responses through mitophagy, metabolic reprogramming, and inflammatory signaling modulation. The protein operates through direct interactions with key signaling molecules including MAVS, STING, LC3, FASTKD5, SLC39A7, and metabolites such as acetyl-CoA. Recent structural and functional studies from 2023-2025 have substantially advanced our molecular understanding, revealing NLRX1 as a sophisticated regulator whose therapeutic targeting holds promise for treating inflammatory, metabolic, and neurodegenerative diseases.
References
(bi2024nlrx1versatilefunctions pages 1-2): Paul Y. Bi, Samuel A. Killackey, Linus Schweizer, and Stephen E. Girardin. Nlrx1: versatile functions of a mitochondrial nlr protein that controls mitophagy. Feb 2024. URL: https://doi.org/10.1016/j.bj.2023.100635, doi:10.1016/j.bj.2023.100635. This article has 26 citations.
(pickering2021nlrinexile pages 1-4): Robert J. Pickering and Lee M. Booty. Nlr in exile: emerging roles of nlrx1 in immunity and human disease. Immunology, 162:268-280, Dec 2021. URL: https://doi.org/10.1111/imm.13291, doi:10.1111/imm.13291. This article has 53 citations and is from a peer-reviewed journal.
(chou2023thenlrgene pages 1-3): Wei-Chun Chou, Sushmita Jha, Michael W. Linhoff, and Jenny P.-Y. Ting. The nlr gene family: from discovery to present day. Nature Reviews Immunology, 23:635-654, Mar 2023. URL: https://doi.org/10.1038/s41577-023-00849-x, doi:10.1038/s41577-023-00849-x. This article has 220 citations and is from a highest quality peer-reviewed journal.
(fekete2021focusingonthe pages 1-2): Tünde Fekete, Dóra Bencze, Eduárd Bíró, Szilvia Benkő, and Kitti Pázmándi. Focusing on the cell type specific regulatory actions of nlrx1. International Journal of Molecular Sciences, 22:1316, Jan 2021. URL: https://doi.org/10.3390/ijms22031316, doi:10.3390/ijms22031316. This article has 38 citations.
(bi2024nlrx1versatilefunctions pages 2-3): Paul Y. Bi, Samuel A. Killackey, Linus Schweizer, and Stephen E. Girardin. Nlrx1: versatile functions of a mitochondrial nlr protein that controls mitophagy. Feb 2024. URL: https://doi.org/10.1016/j.bj.2023.100635, doi:10.1016/j.bj.2023.100635. This article has 26 citations.
(jewell2024insightsintothe pages 1-2): Shannon Jewell, Thanh Binh Nguyen, David B. Ascher, and Avril A.B. Robertson. Insights into the structure of nlr family member x1: paving the way for innovative drug discovery. Dec 2024. URL: https://doi.org/10.1016/j.csbj.2024.09.013, doi:10.1016/j.csbj.2024.09.013. This article has 2 citations and is from a peer-reviewed journal.
(zhang2026cytosolicacetylcoenzymea pages 1-2): Yifan Zhang, Xiao-tong Shen, Yuan Shen, Chao Wang, Chengping Yu, Jiangxue Han, Siyi Cao, Lin Qian, Miaolian Ma, Shijing Huang, Wenyu Wen, Miao Yin, and Qun-Ying Lei. Cytosolic acetyl-coenzyme a is a signalling metabolite to control mitophagy. Nature, 649(8098):1022-1031, Nov 2026. URL: https://doi.org/10.1038/s41586-025-09745-x, doi:10.1038/s41586-025-09745-x. This article has 23 citations and is from a highest quality peer-reviewed journal.
(xiao2025theinnateimmune pages 2-5): Y. Xiao, X. Hu, C. F. Rudolphi, E. E. Nollet, R. Nederlof, Q. Wang, D. Bakker, Panagiota Efstathia Nikolaou, J. C. Knol, R. R. Goeij-de Haas, A. A. Henneman, T. V. Pham, C. R. Jimenez, A. E. Grootemaat, N. N. van der Wel, S. E. Girardin, N. Kaludercic, J. van der Velden, Z. Onódi, P. Leszek, Z. V. Varga, P. Ferdinandy, B. Preckel, N. C. Weber, M. W. Hollmann, F. Di Lisa, and C. J. Zuurbier. The innate immune receptor nlrx1 is a novel required modulator for mptp opening: implications for cardioprotection. Basic Research in Cardiology, 120:707-725, Jun 2025. URL: https://doi.org/10.1007/s00395-025-01124-x, doi:10.1007/s00395-025-01124-x. This article has 8 citations and is from a domain leading peer-reviewed journal.
(xiao2025theinnateimmune pages 5-7): Y. Xiao, X. Hu, C. F. Rudolphi, E. E. Nollet, R. Nederlof, Q. Wang, D. Bakker, Panagiota Efstathia Nikolaou, J. C. Knol, R. R. Goeij-de Haas, A. A. Henneman, T. V. Pham, C. R. Jimenez, A. E. Grootemaat, N. N. van der Wel, S. E. Girardin, N. Kaludercic, J. van der Velden, Z. Onódi, P. Leszek, Z. V. Varga, P. Ferdinandy, B. Preckel, N. C. Weber, M. W. Hollmann, F. Di Lisa, and C. J. Zuurbier. The innate immune receptor nlrx1 is a novel required modulator for mptp opening: implications for cardioprotection. Basic Research in Cardiology, 120:707-725, Jun 2025. URL: https://doi.org/10.1007/s00395-025-01124-x, doi:10.1007/s00395-025-01124-x. This article has 8 citations and is from a domain leading peer-reviewed journal.
(chou2022impactofintracellular pages 7-8): Wei-Chun Chou, Elena Rampanelli, Xin Li, and Jenny P.-Y. Ting. Impact of intracellular innate immune receptors on immunometabolism. Cellular and Molecular Immunology, 19:337-351, Oct 2022. URL: https://doi.org/10.1038/s41423-021-00780-y, doi:10.1038/s41423-021-00780-y. This article has 173 citations and is from a peer-reviewed journal.
(song2024thenlrx1slc39a7complex pages 1-2): Yu Song, Huaizhen Liang, Gaocai Li, Liang Ma, Dingchao Zhu, Weifeng Zhang, Bide Tong, Shuai Li, Yong Gao, Xinghuo Wu, Yukun Zhang, Xiaobo Feng, Kun Wang, and Cao Yang. The nlrx1-slc39a7 complex orchestrates mitochondrial dynamics and mitophagy to rejuvenate intervertebral disc by modulating mitochondrial zn 2+ trafficking. Nov 2024. URL: https://doi.org/10.1080/15548627.2023.2274205, doi:10.1080/15548627.2023.2274205. This article has 72 citations and is from a domain leading peer-reviewed journal.
(pickering2021nlrinexile pages 9-11): Robert J. Pickering and Lee M. Booty. Nlr in exile: emerging roles of nlrx1 in immunity and human disease. Immunology, 162:268-280, Dec 2021. URL: https://doi.org/10.1111/imm.13291, doi:10.1111/imm.13291. This article has 53 citations and is from a peer-reviewed journal.
UniProt: Q86UT6 (NLRX1_HUMAN), 975 aa precursor, HGNC:29890. N-terminal mitochondrial
transit peptide (1-86); NACHT NTPase domain (160-483); C-terminal LRR region (667-975).
Homohexamer (homodimers trimerize). PDB 3UN9 (LRR/RNA-binding element).
NLRX1 is an atypical NOD-like receptor (NLR) that, unlike most NLRs, localizes to the
mitochondrion (outer membrane, with the transit peptide targeting it to mitochondria;
the C-terminal LRR has an RNA-binding element). It is a mitochondrial regulator that sits
at the intersection of antiviral signaling, autophagy/mitophagy, ROS, and inflammasome
control.
Core/established functions:
1. Negative regulation of MAVS-mediated (RIG-I/RLH) antiviral signaling. NLRX1 localizes
to the mitochondrial outer membrane and interacts with MAVS, inhibiting the virus-induced
RIG-I-like-helicase-MAVS interaction and dampening type I interferon induction
PMID:18200010.
2. Promotion of autophagy via TUFM. NLRX1 binds the mitochondrial elongation factor TUFM,
which in turn recruits the autophagy proteins ATG5-ATG12 (ATG16L1), linking NLRX1 to
autophagy induction and modulation of type I IFN [UniProt FUNCTION; PMID:22749352
"The mitochondrial proteins NLRX1 and TUFM form a complex that regulates type I interferon and autophagy"].
The TUFM interaction is also captured by the cached PMID:28611246 (TUFM as a host
restriction factor against avian influenza, correlated with autophagy), where NLRX1-TUFM
is the IPI partner in the GOA. NLRX1 is thus a mitochondrial regulator of autophagy/mitophagy
(TUFM/ATG5-ATG12).
3. Regulation of MAVS-dependent NLRP3 inflammasome activation / attenuation of apoptosis
and inflammation. NLRX1 inhibits MAVS-dependent NLRP3 inflammasome activation, reducing
IL-1beta/IL-18/IL-6 and apoptosis (shown in myocardial ischemia)
PMID:27393910.
4. ROS and NF-kB/JNK modulation. NLRX1 has no inhibitory function on NF-kB itself but
amplifies NF-kB and JNK signaling through ROS production [UniProt FUNCTION; PMID:18219313].
Note the GOA carries an IBA "negative regulation of canonical NF-kappaB signal transduction"
transferred from the mouse ortholog - this is contested (UniProt explicitly states NLRX1
"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").
Mitochondrion / mitochondrial outer membrane (transit peptide; multiple EXP/IDA/HTP/IBA/TAS).
The Reactome cytosol annotation (R-HSA-9749471, "NLRX1 binds CHUK:IKBKB:IKBKG") reflects a
pathway-step model; NLRX1's dominant localization is the mitochondrion. Mitochondrion is the
core compartment.
*-deep-research*.md file found in this gene directory.Autophagy-Lysosome Pathway|Autophagy substrate selection|Selective autophagy receptor|Mitophagy ; PN-node mapping: type→mapped GO:0000423 mitophagy (ancestors no_mapping containers).mapped may over-reach for human NLRX1 if the LIR/mitophagy-receptor role is mouse/infection-specific; recommend confirming before propagating mitophagy as a universal NLRX1 GO assertion. The disputed-NF-κB issue is not in the PN mapping (PN is autophagy-only) so no conflict there.This file is generated from the current PROTEOSTASIS phase-1 dossier and local gene-review artifacts. Edit the source review, PN mapping, or dossier rather than this generated note when correcting the underlying curation.
id: Q86UT6
gene_symbol: NLRX1
product_type: PROTEIN
status: COMPLETE
taxon:
id: NCBITaxon:9606
label: Homo sapiens
description: >-
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.
alternative_products:
- name: '1'
id: Q86UT6-1
- name: '2'
id: Q86UT6-2
sequence_note: VSP_027158, VSP_027159
existing_annotations:
- term:
id: GO:0039536
label: negative regulation of RIG-I signaling pathway
evidence_type: IBA
original_reference_id: GO_REF:0000033
qualifier: involved_in
review:
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.
action: ACCEPT
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.
supported_by:
- reference_id: PMID:18200010
supporting_text: disruption of virus-induced RLH-MAVS interactions
- reference_id: file:human/NLRX1/NLRX1-deep-research-falcon.md
supporting_text: NLRX1 sequesters MAVS and prevents RIG-I/MAVS association, thereby reducing type I interferon and NF-κB responses to RNA viruses
- reference_id: file:human/NLRX1/NLRX1-deep-research-falcon.md
supporting_text: function appears context dependent rather than universally inhibitory
- term:
id: GO:0005739
label: mitochondrion
evidence_type: IBA
original_reference_id: GO_REF:0000033
qualifier: is_active_in
review:
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.
action: ACCEPT
reason: Core localization; NLRX1 is a mitochondrial NLR. The broad mitochondrion term is well supported regardless of which mitochondrial sub-compartment dominates.
supported_by:
- reference_id: PMID:18200010
supporting_text: localizes to the mitochondrial outer membrane and interacts with MAVS
- reference_id: file:human/NLRX1/NLRX1-deep-research-falcon.md
supporting_text: NLRX1 is the only NLR family member to localize to mitochondria
- term:
id: GO:0043124
label: negative regulation of canonical NF-kappaB signal transduction
evidence_type: IBA
original_reference_id: GO_REF:0000033
qualifier: involved_in
review:
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.
action: MARK_AS_OVER_ANNOTATED
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.
supported_by:
- reference_id: file:human/NLRX1/NLRX1-uniprot.txt
supporting_text: 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
- reference_id: file:human/NLRX1/NLRX1-deep-research-falcon.md
supporting_text: NLRX1 negatively regulates NF-κB activation through multiple mechanisms, including binding to TRAF6 (tumor necrosis factor receptor-associated factor 6) to prevent downstream TLR signaling, and interacting with IKK (IκB kinase) to prevent IκB phosphorylation
- term:
id: GO:0005741
label: mitochondrial outer membrane
evidence_type: IEA
original_reference_id: GO_REF:0000044
qualifier: located_in
review:
summary: Electronic transfer of mitochondrial outer membrane localization from the UniProt subcellular location, redundant with the experimental EXP/TAS annotations. Core localization.
action: ACCEPT
reason: Core localization; NLRX1 resides at the mitochondrial outer membrane.
supported_by:
- reference_id: file:human/NLRX1/NLRX1-uniprot.txt
supporting_text: 'SUBCELLULAR LOCATION: Mitochondrion outer membrane'
- term:
id: GO:0005515
label: protein binding
evidence_type: IPI
original_reference_id: PMID:21903422
qualifier: enables
review:
summary: IPI interaction (SARM1, a xeno/mouse partner) from a dynamic innate-immunity interaction network. Bare protein binding is uninformative.
action: KEEP_AS_NON_CORE
reason: High-throughput innate-immunity interactome; bare protein binding is uninformative.
supported_by:
- reference_id: file:human/NLRX1/NLRX1-uniprot.txt
supporting_text: 'Q86UT6; Q6PDS3: Sarm1; Xeno; NbExp=2; IntAct=EBI-3893071, EBI-6117196'
- term:
id: GO:0005515
label: protein binding
evidence_type: IPI
original_reference_id: PMID:28611246
qualifier: enables
review:
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.
action: KEEP_AS_NON_CORE
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.
supported_by:
- reference_id: file:human/NLRX1/NLRX1-uniprot.txt
supporting_text: 'Q86UT6; P49411: TUFM; NbExp=2; IntAct=EBI-3893071, EBI-359097'
- term:
id: GO:0005739
label: mitochondrion
evidence_type: IDA
original_reference_id: GO_REF:0000052
qualifier: located_in
review:
summary: HPA immunofluorescence localization to the mitochondrion, consistent with NLRX1's established mitochondrial localization. Core compartment.
action: ACCEPT
reason: Core localization; NLRX1 is a mitochondrial NLR.
supported_by:
- reference_id: file:human/NLRX1/NLRX1-uniprot.txt
supporting_text: 'SUBCELLULAR LOCATION: Mitochondrion outer membrane'
- term:
id: GO:0005741
label: mitochondrial outer membrane
evidence_type: EXP
original_reference_id: PMID:18200010
qualifier: located_in
review:
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.
action: ACCEPT
reason: Core localization with direct experimental support; the mitochondrial outer membrane is where NLRX1 engages MAVS.
supported_by:
- reference_id: PMID:18200010
supporting_text: localizes to the mitochondrial outer membrane and interacts with MAVS
- term:
id: GO:0005741
label: mitochondrial outer membrane
evidence_type: EXP
original_reference_id: PMID:27393910
qualifier: located_in
review:
summary: Experimental evidence (myocardial ischemia study) that NLRX1 localizes to mitochondria, where it regulates MAVS-dependent NLRP3 inflammasome activation. Core localization.
action: ACCEPT
reason: Core localization with experimental support.
supported_by:
- reference_id: PMID:27393910
supporting_text: NLRX1, located in mitochondria
- term:
id: GO:0005739
label: mitochondrion
evidence_type: HTP
original_reference_id: PMID:34800366
qualifier: located_in
review:
summary: High-throughput proteomic evidence (human mitochondrial proteome) placing NLRX1 in the mitochondrion, consistent with all other evidence. Core compartment.
action: ACCEPT
reason: Core localization; corroborates the experimental mitochondrial localization.
supported_by:
- reference_id: file:human/NLRX1/NLRX1-uniprot.txt
supporting_text: 'SUBCELLULAR LOCATION: Mitochondrion outer membrane'
- term:
id: GO:0005829
label: cytosol
evidence_type: TAS
original_reference_id: Reactome:R-HSA-9749471
qualifier: located_in
review:
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.
action: MARK_AS_OVER_ANNOTATED
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.
supported_by:
- reference_id: file:human/NLRX1/NLRX1-uniprot.txt
supporting_text: 'SUBCELLULAR LOCATION: Mitochondrion outer membrane'
- term:
id: GO:0005741
label: mitochondrial outer membrane
evidence_type: TAS
original_reference_id: Reactome:R-HSA-936564
qualifier: located_in
review:
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.
action: ACCEPT
reason: Core localization; matches the experimental mitochondrial outer membrane evidence and the MAVS-regulation function.
supported_by:
- reference_id: PMID:18200010
supporting_text: localizes to the mitochondrial outer membrane and interacts with MAVS
references:
- id: GO_REF:0000033
title: Annotation inferences using phylogenetic trees
findings: []
- id: GO_REF:0000044
title: Gene Ontology annotation based on UniProtKB/Swiss-Prot Subcellular Location
vocabulary mapping, accompanied by conservative changes to GO terms applied by
UniProt
findings: []
- id: GO_REF:0000052
title: Gene Ontology annotation based on curation of immunofluorescence data
findings: []
- id: PMID:18200010
title: NLRX1 is a regulator of mitochondrial antiviral immunity.
findings:
- statement: NLRX1 localizes to the mitochondrial outer membrane and interacts with MAVS; it potently inhibits RIG-I-like-helicase- and MAVS-mediated IFN-beta promoter activity and disrupts virus-induced RLH-MAVS interactions, and its depletion enhances virus-induced type I IFN and reduces viral replication.
reference_section_type: ABSTRACT
reference_review:
relevance: HIGH
correctness: VERIFIED
review_notes: Foundational study establishing NLRX1 as a mitochondrial outer-membrane negative regulator of MAVS/RIG-I antiviral signaling. Basis of the core localization and RIG-I negative-regulation annotations.
- id: PMID:21903422
title: Mapping a dynamic innate immunity protein interaction network regulating
type I interferon production.
findings: []
- id: PMID:27393910
title: NLRX1 attenuates apoptosis and inflammatory responses in myocardial ischemia
by inhibiting MAVS-dependent NLRP3 inflammasome activation.
findings:
- statement: NLRX1 localizes to mitochondria and inhibits MAVS-dependent NLRP3 inflammasome activation, reducing IL-1beta/IL-18/IL-6, caspase-1 and apoptosis in hypoxia/myocardial-ischemia models.
reference_section_type: ABSTRACT
reference_review:
relevance: HIGH
correctness: VERIFIED
review_notes: Establishes NLRX1's mitochondrial localization and its restraint of MAVS-dependent NLRP3 inflammasome activation / apoptosis.
- id: PMID:28611246
title: Inhibition of Avian Influenza A Virus Replication in Human Cells by Host
Restriction Factor TUFM Is Correlated with Autophagy.
findings:
- statement: TUFM acts as a host restriction factor against avian influenza in a manner correlated with autophagy; NLRX1 is the IntAct partner for the curated NLRX1-TUFM interaction underlying NLRX1's autophagy-promoting function.
reference_section_type: ABSTRACT
reference_review:
relevance: MEDIUM
correctness: VERIFIED
review_notes: Source of the NLRX1-TUFM protein-binding annotation; the TUFM interaction is the mechanistic link to NLRX1's autophagy role (TUFM recruits ATG5-ATG12).
- id: PMID:22749352
title: The mitochondrial proteins NLRX1 and TUFM form a complex that regulates type
I interferon and autophagy.
findings:
- statement: NLRX1 interacts with the mitochondrial elongation factor TUFM, which recruits the autophagy proteins ATG5-ATG12 (and ATG16L1); the NLRX1-TUFM complex promotes autophagy and dampens type I interferon, linking NLRX1 to autophagy/mitophagy.
reference_section_type: ABSTRACT
reference_review:
relevance: HIGH
correctness: VERIFIED
review_notes: Not in the GOA annotation set or cache, but cited in UniProt FUNCTION; primary source for NLRX1's TUFM-dependent autophagy-promoting role. Title/finding from PubMed metadata; full text not in cache.
- id: PMID:18219313
title: NLRX1 is a mitochondrial NOD-like receptor that amplifies NF-kappaB and JNK
pathways by inducing reactive oxygen species production.
findings:
- statement: NLRX1 is a mitochondrial NLR that amplifies NF-kappaB and JNK signaling by inducing reactive oxygen species production (i.e. it does not inhibit NF-kappaB in this study).
reference_section_type: ABSTRACT
reference_review:
relevance: HIGH
correctness: VERIFIED
review_notes: Cited in UniProt FUNCTION. Source of the human-specific view that NLRX1 enhances (rather than inhibits) NF-kappaB/JNK via ROS, which conflicts with the IBA negative-NF-kappaB annotation. Full text not in cache.
- id: PMID:34800366
title: Quantitative high-confidence human mitochondrial proteome and its dynamics
in cellular context.
findings: []
- id: Reactome:R-HSA-936564
title: NLRX1 inhibits MAVS-DDX58 interaction
findings: []
- id: Reactome:R-HSA-9749471
title: NLRX1 binds CHUK:IKBKB:IKBKG
findings: []
- id: file:human/NLRX1/NLRX1-deep-research-falcon.md
title: Falcon deep research report for NLRX1
findings:
- statement: LLM-synthesized review of NLRX1 emphasizing an emerging "unifying" mitophagy-receptor model (direct LC3 binding, acetyl-CoA metabolite sensing), multi-compartment mitochondrial localization (matrix, inner membrane, outer membrane), and negative regulation of RIG-I/MAVS, cGAS-STING and NF-kappaB, while explicitly noting context-/cell-type-dependence of the antiviral effects.
reference_section_type: OTHER
reference_review:
relevance: MEDIUM
correctness: UNVERIFIED
review_notes: >-
LLM synthesis (Edison/Falcon) built almost entirely from recent secondary reviews
(Bi 2024, Pickering 2021, Chou 2023/2022, Jewell 2024) and very recent primary papers
(Xiao 2025 mPTP; Zhang 2026 acetyl-CoA; Song 2024 SLC39A7) that are NOT in the local
publications cache, so the cited claims could not be verified against primary text and
are marked UNVERIFIED. Several claims are debated or go beyond what the cached primary
literature shows: (1) Localization - falcon asserts NLRX1 is in the matrix and inner
mitochondrial membrane in addition to the outer membrane, whereas the foundational
cached papers (PMID:18200010, PMID:22749352) place its MAVS-regulatory activity at the
mitochondrial outer membrane; the matrix/inner-membrane and mPTP claims rest on
uncached 2024-2025 work. (2) Mitophagy - falcon frames direct NLRX1-LC3 binding and
mitophagy as the overarching function, but the cached full-text PMID:22749352 states
mitophagy "was not occurring under these test conditions" and that NLRX1 promotes
(non-selective) autophagy indirectly via TUFM/ATG5-ATG12, not by direct LC3 binding;
the LC3-receptor/acetyl-CoA model is newer and not independently verified here.
(3) NF-kappaB - falcon (citing reviews) reports NLRX1 NEGATIVELY regulates NF-kappaB,
which contradicts the human-specific cached primary report (PMID:18219313) that NLRX1
AMPLIFIES NF-kappaB/JNK via ROS; this confirms the field is genuinely mixed. Useful as a
pointer to recent literature and to flag controversy, but not used as sole support for
any annotation action change.
core_functions:
- description: Acts as a mitochondrial outer-membrane negative regulator of MAVS-mediated
(RIG-I-like helicase) antiviral signaling - interacting with MAVS to disrupt the
virus-induced RIG-I-MAVS interaction and dampen type I interferon production.
molecular_function:
id: GO:0060090
label: molecular adaptor activity
locations:
- id: GO:0005741
label: mitochondrial outer membrane
supported_by:
- reference_id: PMID:18200010
supporting_text: disruption of virus-induced RLH-MAVS interactions
directly_involved_in:
- id: GO:0039536
label: negative regulation of RIG-I signaling pathway
- description: Promotes autophagy by binding the mitochondrial elongation factor TUFM,
which recruits the autophagy machinery (ATG5-ATG12, ATG16L1); this couples NLRX1 to
autophagy and to modulation of type I interferon. Recent reviews additionally propose
NLRX1 acts as a mitophagy receptor that directly engages LC3, but the cached primary
full text (PMID:22749352) reports indirect, TUFM-mediated autophagy and did not observe
mitophagy under its conditions, so the direct-LC3 mitophagy-receptor model remains an
emerging, not yet locally verified, refinement.
molecular_function:
id: GO:0060090
label: molecular adaptor activity
locations:
- id: GO:0005741
label: mitochondrial outer membrane
supported_by:
- reference_id: PMID:22749352
supporting_text: The mitochondrial proteins NLRX1 and TUFM form a complex that regulates type I interferon and autophagy
- reference_id: PMID:22749352
supporting_text: 'autophagy of mitochondria (mitophagy) was not occurring under these test conditions'
- reference_id: file:human/NLRX1/NLRX1-deep-research-falcon.md
supporting_text: mitophagy regulation may represent the overarching unifying function of NLRX1
directly_involved_in:
- id: GO:0010508
label: positive regulation of autophagy
- description: Restrains MAVS-dependent NLRP3 inflammasome activation, limiting IL-1beta/
IL-18 production and apoptosis, and modulates reactive oxygen species production with
downstream effects on NF-kappaB and JNK signaling.
molecular_function:
id: GO:0060090
label: molecular adaptor activity
locations:
- id: GO:0005741
label: mitochondrial outer membrane
supported_by:
- reference_id: PMID:27393910
supporting_text: regulated MAVS-dependent NLRP3 inflammasome activation
proposed_new_terms:
- proposed_name: positive regulation of autophagy
proposed_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.
proposed_parent:
id: GO:0010508
label: positive regulation of autophagy
supported_by:
- reference_id: PMID:22749352
supporting_text: The mitochondrial proteins NLRX1 and TUFM form a complex that regulates type I interferon and autophagy
- reference_id: file:human/NLRX1/NLRX1-uniprot.txt
supporting_text: promotes autophagy by interacting with TUFM and subsequently recruiting the autophagy-related proteins ATG5 and ATG12
suggested_questions:
- question: 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?
- question: 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?
- question: 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?
suggested_experiments:
- description: 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.
- description: 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.