NMNAT2 (nicotinamide/nicotinate mononucleotide adenylyltransferase 2) is one of three human NMNAT isoforms and catalyzes the central, committed adenylyl-transfer step of NAD+ biosynthesis: it condenses nicotinamide mononucleotide (NMN) with ATP to form NAD+ (EC 2.7.7.1), and less efficiently condenses nicotinate mononucleotide (NaMN) with ATP to form deamido-NAD+ (NaAD; EC 2.7.7.18), releasing pyrophosphate in each case. This reaction is shared by the NAD+ salvage and de novo routes. The active enzyme is a Mg2+-dependent monomer. Unlike the nuclear isoform NMNAT1 and the mitochondrial NMNAT3, NMNAT2 is a cytosolic, Golgi/Golgi-derived-vesicle-membrane-associated enzyme; membrane attachment requires palmitoylation, and the protein is trafficked into axons on Golgi-derived vesicles. NMNAT2 is highly expressed in brain and is a labile, short-lived protein. Its continuous supply is a key axon-maintenance/survival factor: by sustaining local NAD+ (and consuming NMN) it keeps the pro-degenerative NADase SARM1 inactive, thereby delaying Wallerian-type axon degeneration; loss or depletion of NMNAT2 triggers axon degeneration and, in mice, perinatal lethality with severe axon defects. In cytosolic NAD+-supply roles it can also support the mono-ADP-ribosyltransferase PARP16, promoting ribosomal-protein MARylation that tunes cytoplasmic translation. Biallelic loss-of-function variants cause a human polyneuropathy with skeletal abnormalities.
| GO Term | Evidence | Action | Reason |
|---|---|---|---|
| GO:0004515 nicotinate-nucleotide adenylyltransferase activity | IBA GO_REF:0000033 | ACCEPT | Summary: Phylogenetic (IBA) transfer of the nicotinate-nucleotide adenylyltransferase (EC 2.7.7.18) activity across the eukaryotic NMN adenylyltransferase family. This is directly supported for human NMNAT2 by experimental assays (PMID:16118205, PMID:17402747) and by UniProt EC=2.7.7.18. One of the two core catalytic activities. |
| GO:0005794 Golgi apparatus | IBA GO_REF:0000033 | ACCEPT | Summary: Phylogenetic assignment of Golgi localization, consistent with experimental data showing NMNAT2 is associated with the cytoplasmic face of the Golgi apparatus (PMID:16118205). Golgi/Golgi-derived-vesicle association is a defining, core feature of this isoform. |
| GO:0000309 nicotinamide-nucleotide adenylyltransferase activity | IBA GO_REF:0000033 | ACCEPT | Summary: Phylogenetic (IBA) transfer of the nicotinamide-nucleotide adenylyltransferase (EC 2.7.7.1, NMN + ATP -> NAD+) activity. This is the primary, evolutionarily conserved catalytic function of NMNAT2 and is experimentally confirmed for the human enzyme (PMID:16118205, PMID:17402747). Core molecular function. |
| GO:0034355 NAD+ biosynthetic process via the salvage pathway | IBA GO_REF:0000033 | ACCEPT | Summary: Phylogenetic assignment placing NMNAT2 in NAD+ biosynthesis via the salvage pathway. NMNAT2 catalyzes the final adenylylation step (NMN -> NAD+) that is shared by the salvage route; a correct and informative more-specific child of the general NAD+ biosynthetic process. Core biological process. |
| GO:0000139 Golgi membrane | IEA GO_REF:0000044 | ACCEPT | Summary: Golgi membrane location mapped electronically from the UniProt Subcellular Location keyword. Correct and experimentally corroborated: NMNAT2 associates with the Golgi apparatus membrane (PMID:16118205). Core location; redundant with the EXP/TAS Golgi-membrane annotations below. |
| GO:0000309 nicotinamide-nucleotide adenylyltransferase activity | IEA GO_REF:0000120 | ACCEPT | Summary: Electronic assignment of the core EC 2.7.7.1 (NMN + ATP -> NAD+) activity via InterPro/RHEA/EC mapping. Consistent with the experimental annotations; core molecular function. |
| GO:0003824 catalytic activity | IEA GO_REF:0000002 | MARK AS OVER ANNOTATED | Summary: Root-level catalytic activity assigned electronically from an InterPro domain (cytidylyltransferase- like fold). Not incorrect, but far too general given that the specific adenylyltransferase activities (GO:0000309, GO:0004515) are experimentally established for this protein. |
| GO:0004515 nicotinate-nucleotide adenylyltransferase activity | IEA GO_REF:0000120 | ACCEPT | Summary: Electronic assignment of the EC 2.7.7.18 (NaMN + ATP -> deamido-NAD+) activity via InterPro/RHEA/EC mapping. Experimentally confirmed for the human enzyme (PMID:16118205, PMID:17402747). Core molecular function (secondary, lower-efficiency substrate). |
| GO:0005737 cytoplasm | IEA GO_REF:0000044 | ACCEPT | Summary: Cytoplasm location mapped from the UniProt Subcellular Location keyword. Correct and experimentally supported (PMID:16118205); NMNAT2 acts in the cytoplasm/cytosol. The more specific cytosol (GO:0005829) IDA and the Golgi-membrane annotations are more informative. |
| GO:0009165 nucleotide biosynthetic process | IEA GO_REF:0000117 | MARK AS OVER ANNOTATED | Summary: General nucleotide biosynthetic process assigned by an ARBA machine-learning model. True but much less informative than the specific NAD+ biosynthetic process (GO:0009435) and its salvage child, which are also annotated. Kept as a correct high-level parent. |
| GO:0009435 NAD+ biosynthetic process | IEA GO_REF:0000120 | ACCEPT | Summary: NAD+ biosynthetic process assigned electronically via InterPro/UniPathway. This is the core pathway role of NMNAT2, which catalyzes the final adenylylation step of NAD+ synthesis (PMID:16118205, PMID:17402747). Core biological process. |
| GO:0030424 axon | IEA GO_REF:0000044 | KEEP AS NON CORE | Summary: Axon location mapped from the UniProt Subcellular Location keyword (cell projection, axon; by similarity to mouse Q8BNJ3). Biologically appropriate: NMNAT2 is trafficked into axons on Golgi-derived vesicles and its axonal presence underlies its axon-maintenance role. Genuine but non-core relative to the enzymatic activity. |
| GO:0030659 cytoplasmic vesicle membrane | IEA GO_REF:0000044 | ACCEPT | Summary: Cytoplasmic vesicle membrane location mapped from the UniProt Subcellular Location keyword. Consistent with delivery of NMNAT2 to axons on Golgi-derived cytoplasmic vesicles (palmitoylation- dependent membrane anchoring). Duplicated by the ISS annotation below; accept as a correct location. |
| GO:0005829 cytosol | IDA GO_REF:0000052 | ACCEPT | Summary: Cytosol localization from Human Protein Atlas immunofluorescence (IDA). Consistent with NMNAT2 acting in the cytoplasm/cytosol and with its Golgi-membrane/vesicle association. Core location. |
| GO:0000309 nicotinamide-nucleotide adenylyltransferase activity | IDA PMID:16118205 Subcellular compartmentation and differential catalytic prop... | ACCEPT | Summary: Direct experimental assay (Berger et al. 2005) of human NMNAT2 catalyzing NAD+ formation from NMN and ATP (EC 2.7.7.1). This is the primary, defining catalytic activity of the enzyme; the abstract states NMNAT is "the central enzyme of the NAD biosynthetic pathway". Core molecular function. |
| GO:0000139 Golgi membrane | EXP PMID:16118205 Subcellular compartmentation and differential catalytic prop... | ACCEPT | Summary: Experimental subcellular-localization study (Berger et al. 2005) placing NMNAT2 at the Golgi complex, distinguishing it from nuclear NMNAT1 and mitochondrial NMNAT3. Golgi(-membrane) association is a defining, core feature of this isoform. |
| GO:0000309 nicotinamide-nucleotide adenylyltransferase activity | EXP PMID:17402747 Initial-rate kinetics of human NMN-adenylyltransferases: sub... | ACCEPT | Summary: Experimental initial-rate kinetics (Sorci et al. 2007) confirming NMNAT2 as an NMN adenylyltransferase (EC 2.7.7.1) with defined substrate and metal-ion specificity. Corroborates the core NMN -> NAD+ activity. |
| GO:0004515 nicotinate-nucleotide adenylyltransferase activity | EXP PMID:17402747 Initial-rate kinetics of human NMN-adenylyltransferases: sub... | ACCEPT | Summary: Experimental kinetics (Sorci et al. 2007) confirming NMNAT2 can also use the deamidated substrate nicotinate mononucleotide (NaMN + ATP -> deamido-NAD+, EC 2.7.7.18). Core molecular function (secondary substrate). |
| GO:0005737 cytoplasm | EXP PMID:16118205 Subcellular compartmentation and differential catalytic prop... | ACCEPT | Summary: Experimental localization (Berger et al. 2005) supporting a cytoplasmic pool of NMNAT2 in addition to its Golgi-membrane association. Correct core location; the specific cytosol (GO:0005829) term is more informative. |
| GO:0030659 cytoplasmic vesicle membrane | ISS GO_REF:0000024 | ACCEPT | Summary: Cytoplasmic vesicle membrane location transferred by sequence similarity from mouse Nmnat2 (Q8BNJ3). Consistent with NMNAT2 being palmitoylated and delivered to axons on Golgi-derived cytoplasmic vesicles. Correct; duplicates the IEA cytoplasmic-vesicle-membrane annotation. |
| GO:0061564 axon development | ISS PMID:30304512 Low levels of NMNAT2 compromise axon development and surviva... | KEEP AS NON CORE | Summary: Axon development role, transferred by similarity to mouse Nmnat2, supported by Gilley et al. 2019: NMNAT2 is "an endogenous axon maintenance factor that preserves axon health by blocking Wallerian-like axon degeneration", mice lacking it "die at birth with severe axon defects", and reduced levels compromise peripheral axon development. This axon-maintenance/development role is genuine and physiologically important, but the primary evolved function is the adenylyltransferase activity, so this is kept as non-core. |
| GO:0140768 protein ADP-ribosyltransferase-substrate adaptor activity | IDA PMID:34314702 Ribosome ADP-ribosylation inhibits translation and maintains... | KEEP AS NON CORE | Summary: Challa et al. 2021 show NMNAT2 supports PARP16 (a mono-ADP-ribosyltransferase) activity toward ribosomal proteins, with NMNAT2 and PARP16 physically interacting and catalytically active NMNAT2 enhancing PARP16 auto-MARylation. This is a context-specific (cytosolic NAD+ supply, high-PARP16 ovarian cancer) moonlighting role largely mediated through NAD+ production rather than the core metabolic function. Experimental IDA; retained as non-core. |
| GO:2000766 negative regulation of cytoplasmic translation | IDA PMID:34314702 Ribosome ADP-ribosylation inhibits translation and maintains... | KEEP AS NON CORE | Summary: Challa et al. 2021 show NMNAT2 (via PARP16-mediated ribosomal-protein MARylation) inhibits protein synthesis in a manner dependent on its catalytic activity, tuning cytoplasmic translation and proteostasis in cancer cells. Experimental IDA, but a specialized downstream/context-specific role rather than the core NAD+-biosynthetic function; kept as non-core. |
| GO:0009165 nucleotide biosynthetic process | IC PMID:16118205 Subcellular compartmentation and differential catalytic prop... | MARK AS OVER ANNOTATED | Summary: Curator inference (IC) of the general nucleotide biosynthetic process from the demonstrated nicotinate-nucleotide adenylyltransferase activity. Correct but high-level; the specific NAD+ biosynthetic process (GO:0009435) and its salvage child capture the role more precisely. |
| GO:0004515 nicotinate-nucleotide adenylyltransferase activity | IDA PMID:16118205 Subcellular compartmentation and differential catalytic prop... | ACCEPT | Summary: Direct experimental assay (Berger et al. 2005) of the EC 2.7.7.18 activity (NaMN + ATP -> deamido-NAD+) for human NMNAT2. Core molecular function (secondary substrate). Redundant with the EXP annotation from PMID:17402747. |
| GO:0005794 Golgi apparatus | IDA PMID:16118205 Subcellular compartmentation and differential catalytic prop... | ACCEPT | Summary: Direct experimental localization (Berger et al. 2005) of NMNAT2 to the Golgi apparatus. A defining, core feature distinguishing this isoform from nuclear NMNAT1 and mitochondrial NMNAT3. |
| GO:0000139 Golgi membrane | TAS Reactome:R-HSA-197235 | ACCEPT | Summary: Reactome traceable-author statement (NMNAT2 NaMN -> NaAD reaction) placing the enzyme at the cytoplasmic face of the Golgi membrane. Consistent with the experimental Golgi localization; core location. |
| GO:0000139 Golgi membrane | TAS Reactome:R-HSA-8939959 | ACCEPT | Summary: Reactome traceable-author statement (NMNAT2 NMN -> NAD+ reaction) placing the enzyme at the Golgi membrane. Consistent with the experimental Golgi localization; core location. |
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Download this section (compressed HTML)Q: Is the axon-maintenance function of NMNAT2 fully attributable to its NAD+-biosynthetic activity (and consequent SARM1 suppression via NMN consumption), or does NMNAT2 also have activity- independent (e.g. chaperone-like) contributions to axon survival?
Q: How central is the PARP16-adaptor / translation-regulatory role of NMNAT2 outside the cancer context in which it was characterized, and is it relevant in neurons?
Q: What is the spectrum and mechanism of NMNAT2-related human disease (childhood-onset polyneuropathy with skeletal abnormalities) and how does it relate to the murine perinatal-lethal axon phenotype?
Experiment: Quantify axonal NAD+/NMN and SARM1 activation in human neurons upon graded NMNAT2 depletion versus catalytic-dead (H24 / W92) rescue, to separate metabolic from non-metabolic contributions to axon survival.
Experiment: Structural and enzyme-kinetic comparison of the three human NMNAT isoforms under matched conditions to define isoform-specific substrate preferences (NMN vs NaMN vs NMNH) relevant to compartmentalized NAD+ pools.
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