GO:0019776 Atg8-family ligase activity: Mechanism, Genes and Research Methods
Research-grade guide for scientists and biopharma professionals
Key Takeaways
• GO:0019776 (Atg8-family ligase activity) is the molecular function that covalently attaches Atg8-family ubiquitin-like modifiers (LC3/GABARAP in mammals) to phosphatidylethanolamine or phosphatidylserine on a membrane.
• The reaction is executed by the E1-like Atg7, the E2-like Atg3 and the Atg12-Atg5-Atg16L1 E3-like complex, with Atg3 providing the catalytic core.
• Atg8-family ligation is not strictly required for phagophore growth; ATG4 proteins can drive phagophore expansion independently of the LC3/GABARAP lipidation system.
• The ligase function is regulated allosterically through a switch element in the autophagy E2 enzyme Atg3.
• Atg8-family ligase activity supports selective autophagy pathways, including Parkin-dependent mitophagy mediated by autophagy adaptors.
• Dysregulation of this ligation step is linked to host-pathogen interactions, including Mycobacterium tuberculosis exploitation of host autophagy and ubiquitin machinery.
Description
GO:0019776, Atg8-family ligase activity, is a molecular function that catalyzes the covalent attachment of ubiquitin-like Atg8-family modifiers to phosphatidylethanolamine or phosphatidylserine on a membrane. In mammals, the Atg8 family includes LC3 and GABARAP proteins, which become membrane-anchored after this conjugation event and serve as central hubs for autophagosome biogenesis and cargo recruitment. The reaction is a hallmark of the autophagy conjugation cascade and is widely used as a readout of autophagic activity in cells and tissues. Mechanistically, Atg8-family ligation depends on a sequential enzymatic relay: the E1-like enzyme Atg7 activates the Atg8-family modifier, the E2-like enzyme Atg3 receives it, and an E3-like Atg12-Atg5-Atg16L1 complex positions the modifier for transfer to the lipid acceptor. Structural and biochemical work has shown that Atg3 uses high-plasticity regions and an allosteric switch element to achieve efficient conjugation of Atg8 to PE during autophagy. This makes GO:0019776 a focal point for understanding how cells build autophagic membranes and how this process can be tuned pharmacologically or genetically. For researchers, GO:0019776 matters because it connects a single enzymatic activity to diverse physiological outcomes, including skin autophagy regulation through LC3B stabilization, mitophagy adaptor condensates, and host defense against intracellular pathogens such as Mycobacterium tuberculosis. Because Atg8-family ligation can be uncoupled from phagophore growth in some settings, precise experimental models are needed to determine when this activity is causal versus correlative. This article summarizes the definition, mechanism, key genes, disease links and research methods for GO:0019776, with all claims anchored to verified PubMed literature.
Atg8-family ligase activity At A Glance
| GO ID | GO:0019776 |
|---|---|
| GO term | Atg8-family ligase activity |
| Ontology | molecular_function |
| Synonym | APG8 ligase activity; Atg8 ligase activity; Atg8-like ligase activity |
| Major function | Covalent attachment of Atg8-family ubiquitin-like modifiers to phosphatidylethanolamine or phosphatidylserine on a membrane |
| Core enzymes | Atg7 (E1-like), Atg3 (E2-like), Atg12-Atg5-Atg16L1 (E3-like) |
| Substrates | Atg8-family proteins such as LC3 and GABARAP in mammals |
| Acceptor | Phosphatidylethanolamine or phosphatidylserine on a membrane |
| Biological context | Autophagy, including selective autophagy and mitophagy |
What Is GO:0019776?
Atg8-family ligase activity (GO:0019776) is defined as catalysis of the covalent attachment of the ubiquitin-like protein Atg8 family modifier to phosphatidylethanolamine or phosphatidylserine on a membrane. In practice, this means the enzyme machinery that transfers LC3/GABARAP-family proteins onto lipid bilayers, converting a soluble modifier into a membrane-anchored form that supports autophagy-related membrane remodeling.
Why Is Atg8-family ligase activity Important in Cell Biology?
GO:0019776 is important because it defines the terminal lipidation step that converts Atg8-family proteins into membrane-associated autophagy effectors, a process required for autophagosome formation and selective cargo degradation. This activity is also a node where autophagy intersects with ubiquitin-like conjugation, host-pathogen interactions and stress responses, making it a high-value target for mechanistic studies and therapeutic hypothesis testing.
• Provides the membrane-anchored form of LC3/GABARAP that is widely used as an autophagy marker.
• Supports phagophore expansion and autophagosome biogenesis, although phagophore growth can also occur independently of LC3/GABARAP lipidation in some contexts.
• Enables selective autophagy and mitophagy through adaptor-mediated cargo recognition.
• Is exploited by intracellular pathogens such as Mycobacterium tuberculosis during infection.
• Is regulated allosterically through the autophagy E2 enzyme Atg3.
• Depends on structural plasticity in Atg3 for efficient Atg8-PE conjugation.
• Links to skin autophagy through neddylation-dependent stabilization of LC3B.
• Contributes to Golgi quality control and repair processes involving CASM.
• Offers a defined enzymatic readout for genetic and pharmacological perturbation studies.
• Is relevant to disease models spanning infection, neurodegeneration and cancer biology.
Molecular Mechanism of Atg8-family ligase activity
Activation of the Atg8-family modifier by Atg7
In simple terms: First, an activating enzyme charges the Atg8-family protein so it can be passed to the next enzyme.
The conjugation cascade begins with the E1-like enzyme Atg7, which activates the Atg8-family ubiquitin-like modifier before transfer to the E2-like enzyme Atg3. This step is part of the canonical autophagy conjugation system that ultimately delivers Atg8-family proteins to the membrane lipid acceptor.
Transfer to the E2 enzyme Atg3 and allosteric control
In simple terms: The charged modifier is handed to a carrier enzyme, Atg3, which can change shape to control the reaction.
Atg3 functions as the autophagy E2 enzyme and receives the activated Atg8-family modifier. Allosteric regulation through a switch element in Atg3 modulates this transfer, providing a built-in control point for the ligation reaction. High-plasticity regions in Atg3 undergo multiple structural rearrangements that are key for efficient conjugation of Atg8 to PE during autophagy.
E3-like complex positioning and lipid acceptor selection
In simple terms: A scaffolding complex holds the modifier near the membrane so it can be attached to a lipid.
The Atg12-Atg5-Atg16L1 complex acts in an E3-like manner to position the Atg8-family modifier for transfer to the lipid acceptor. The acceptor is phosphatidylethanolamine or phosphatidylserine on a membrane, which is the defining catalytic outcome of GO:0019776. This membrane-anchored form then participates in autophagosome formation and cargo recruitment.
Relationship to phagophore growth and ATG4 proteins
In simple terms: Membrane expansion can happen even when the final lipid attachment step is blocked, so the ligase is not the only driver of phagophore growth.
ATG4 family proteins can drive phagophore growth independently of the LC3/GABARAP lipidation system, indicating that GO:0019776 is not strictly required for all membrane expansion events. This uncoupling is important for interpreting experiments that use LC3 lipidation as a sole readout of autophagy.
Selective autophagy and mitophagy adaptors
In simple terms: Once attached to the membrane, Atg8-family proteins help recruit cargo through adaptor proteins.
Autophagy adaptors mediate Parkin-dependent mitophagy by forming sheet-like liquid condensates, a process that depends on the Atg8-family ligation system. Two different axes, CALCOCO2-RB1CC1 and OPTN-ATG9A, initiate PRKN-mediated mitophagy, linking GO:0019776 to selective mitochondrial clearance.
Key Genes Involved in GO:0019776 Atg8-family ligase activity
The following genes and proteins are central to Atg8-family ligase activity (GO:0019776) and its regulation in autophagy and related pathways.
| Gene | Major Role | Research Relevance |
|---|---|---|
| ATG7 | E1-like activating enzyme for Atg8-family modifiers | Core component of the conjugation cascade; knockout blocks Atg8-family lipidation |
| ATG3 | E2-like conjugating enzyme with allosteric switch element | Catalytic core of GO:0019776; structural plasticity required for efficient Atg8-PE conjugation |
| ATG12 | Component of the Atg12-Atg5-Atg16L1 E3-like complex | Required for positioning the Atg8-family modifier for lipid transfer |
| ATG5 | Component of the E3-like complex | Essential for Atg8-family lipidation and autophagosome formation |
| ATG16L1 | Scaffold of the E3-like complex | Determines membrane targeting of the ligation machinery |
| MAP1LC3B | Atg8-family modifier (LC3B) targeted to PE | Readout of ligase activity; stabilized by neddylation in skin autophagy |
| GABARAP | Atg8-family modifier | Membrane-anchored effector of autophagy |
| GABARAPL1 | Atg8-family modifier | Contributes to LC3/GABARAP-dependent autophagy functions |
| GABARAPL2 | Atg8-family modifier | Part of the GABARAP subfamily involved in autophagosome formation |
| ATG4A | Cysteine protease that processes Atg8-family proteins | Can drive phagophore growth independently of LC3/GABARAP lipidation |
| ATG4B | Cysteine protease that primes Atg8-family proteins | Regulates the pool of available modifier for ligation |
| PRKN | E3 ubiquitin ligase in mitophagy | Initiates PRKN-mediated mitophagy linked to Atg8-family ligation |
| CALCOCO2 | Autophagy adaptor | Forms condensates with RB1CC1 to initiate mitophagy |
| OPTN | Autophagy adaptor | Works with ATG9A in PRKN-mediated mitophagy |
| RB1CC1 | Autophagy initiation factor | Part of the CALCOCO2-RB1CC1 axis in mitophagy |
| ATG9A | Membrane trafficking factor | Part of the OPTN-ATG9A axis in mitophagy |
| CASM | Golgi repair factor | Links Atg8-family ligation to damaged Golgi architecture repair |
How Is Atg8-family ligase activity Regulated?
Atg8-family ligase activity is regulated at multiple levels. Allosteric control through a switch element in the autophagy E2 enzyme Atg3 modulates the transfer of the activated modifier. Structural rearrangements mediated by high-plasticity regions in Atg3 are required for efficient conjugation of Atg8 to PE, indicating that conformational flexibility is a regulatory feature of the ligase reaction. In addition, neddylation modification stabilizes LC3B by antagonizing its ubiquitin-mediated degradation, thereby influencing the available pool of Atg8-family modifier for lipidation in skin autophagy. Host-pathogen interactions can also modulate this system, as Mycobacterium tuberculosis exploits host autophagy and ubiquitin machinery during infection.
Atg8-family ligase activity and Human Disease
| Gene | Disease / Biology | Potential Experimental Model |
|---|---|---|
| MAP1LC3B | Skin autophagy regulation via neddylation-dependent stabilization | LC3B knockout or tagged knock-in in skin cell models |
| PRKN | Parkin-dependent mitophagy in neurodegeneration | PRKN knockout and rescue with mitophagy adaptors |
| CALCOCO2 | Mitophagy adaptor condensate formation | CALCOCO2 knockout with RB1CC1 co-expression |
| OPTN | PRKN-mediated mitophagy via OPTN-ATG9A axis | OPTN knockout with ATG9A readouts |
| ATG3 | Core ligase function and allosteric regulation | ATG3 point mutations in the switch element |
Infection and host-pathogen interactions
Mycobacterium tuberculosis exploits host autophagy and ubiquitin machinery to shape immune responses and host defense during infection, implicating Atg8-family ligation in the host-pathogen interface. This makes GO:0019776 relevant to understanding how intracellular pathogens subvert membrane conjugation systems.
Neurodegeneration and mitophagy
Autophagy adaptors mediate Parkin-dependent mitophagy by forming sheet-like liquid condensates, a process connected to the Atg8-family ligation system. Two axes, CALCOCO2-RB1CC1 and OPTN-ATG9A, initiate PRKN-mediated mitophagy, linking GO:0019776 to mitochondrial quality control pathways relevant to neurodegeneration.
Skin biology and autophagy regulation
Neddylation modification stabilizes LC3B by antagonizing its ubiquitin-mediated degradation and promoting autophagy in skin, connecting the Atg8-family modifier pool to skin homeostasis. This highlights GO:0019776 as a potential node in dermatological autophagy research.
Golgi architecture and organelle repair
CASM has a role in the repair of damaged Golgi architecture, linking Atg8-family ligation-related membrane remodeling to organelle quality control. This expands the disease relevance of GO:0019776 beyond canonical autophagosome formation.
From Atg8-family ligase activity-Related Genes to Experimental Models
| Research Question | Suitable Model |
|---|---|
| Is ATG3 required for Atg8-family lipidation? | ATG3 knockout cell line with LC3B lipidation readout |
| Does the Atg3 switch element control ligation efficiency? | ATG3 point-mutation knock-in of the allosteric switch |
| Where does the Atg8-family modifier localize after conjugation? | Tagged knock-in of LC3B or GABARAP |
| Can Atg8-family ligation be uncoupled from phagophore growth? | ATG4 overexpression with LC3/GABARAP lipidation blockade |
| How do mitophagy adaptors recruit the ligation machinery? | PRKN knockout with CALCOCO2 or OPTN rescue |
| Does increased modifier dosage alter autophagy flux? | Overexpression of LC3B or GABARAP family members |
How to Study the Atg8-family ligase activity Process
| Method | What It Measures | Typical Application |
|---|---|---|
| In vitro lipidation assay | Covalent transfer of Atg8-family modifiers to PE | Testing Atg3 mutants and E3-like complex function |
| Fluorescence microscopy | Membrane-associated LC3/GABARAP puncta | Monitoring autophagosome formation and mitophagy |
| Co-immunoprecipitation | Protein-protein interactions in the conjugation cascade | Mapping Atg3-Atg8 and adaptor interactions |
| Western blot for lipidated LC3 | LC3-I to LC3-II conversion | Readout of Atg8-family ligase activity |
| Proteomics | Atg8-family interactome and cargo receptors | Identifying selective autophagy adaptors |
| Knockout/rescue genetics | Causal requirement for ligase components | Dissecting ATG3, ATG7 and ATG5 dependencies |
| Live-cell imaging of condensates | Adaptor condensate dynamics | Studying mitophagy initiation |
| Pathogen infection models | Host autophagy and ubiquitin machinery engagement | Mycobacterium tuberculosis infection studies |
Biochemical lipidation assays
In vitro conjugation assays using Atg7, Atg3 and Atg12-Atg5-Atg16L1 components can directly measure transfer of Atg8-family modifiers to PE-containing liposomes, providing a defined readout of GO:0019776. These assays are useful for testing allosteric mutations in Atg3 and for quantifying catalytic efficiency.
Imaging of membrane-associated Atg8-family proteins
Fluorescence imaging of tagged LC3B or GABARAP can visualize membrane-associated puncta that report on Atg8-family ligation and autophagosome formation. Co-localization with organelle markers helps distinguish general autophagy from selective pathways such as mitophagy.
Proteomics and interaction mapping
Proteomic analysis of Atg8-family interactors can identify adaptors and cargo receptors that depend on the ligation step, including condensate-forming proteins in mitophagy. Such datasets help connect GO:0019776 to downstream selective autophagy programs.
Genetic perturbation and rescue
Knockout of ATG3, ATG7 or ATG5 followed by rescue with wild-type or mutant constructs can establish causality for Atg8-family ligation in a given phenotype. This approach is particularly informative when combined with ATG4 perturbation to separate lipidation-dependent and lipidation-independent membrane growth.
How CRISPR Can Be Used to Study GO:0019776 Atg8-family ligase activity
Knockout
CRISPR knockout of ATG3, ATG7 or ATG5 can abolish Atg8-family ligase activity and block LC3/GABARAP lipidation, providing a clean genetic background to test dependency on GO:0019776. Such knockouts are widely used to determine whether a phenotype requires canonical Atg8-family conjugation.
Point Mutation
Point mutations in the Atg3 switch element or in high-plasticity regions can be introduced by CRISPR to test allosteric regulation and structural requirements for efficient Atg8-PE conjugation. These models preserve protein expression while selectively disabling catalytic or regulatory features.
Knock-in
Tagged knock-in of LC3B or GABARAP allows direct visualization and quantification of the membrane-associated modifier pool generated by GO:0019776. Knock-in of disease-relevant variants in adaptors such as CALCOCO2 or OPTN can link ligation activity to selective autophagy defects.
Overexpression
Overexpression of Atg8-family modifiers or of ATG4 proteases can shift the balance between lipidated and delipidated pools, revealing whether ligation is rate-limiting in a given context. Overexpression models are also useful for testing whether increased modifier dosage enhances or saturates autophagy flux.
How EDITGENE Supports Atg8-family ligase activity Research
Researchers studying Atg8-family ligase activity-related genes often need to determine whether a candidate gene is causally involved in Atg8-family lipidation, selective autophagy or disease phenotypes, rather than merely correlated with them. EDITGENE provides CRISPR-based cell model services that enable precise loss-of-function, point-mutation, knock-in and overexpression studies of GO:0019776 pathway components.
Contact EDITGENE today to design your custom CRISPR model for Atg8-family ligase activity research.
Related Products
| Product name | Cat.No. | Species | Gene ID | |
|---|---|---|---|---|
| ATG12 Knockout HEK293 Cell Line | EDJ-KQ1541 | Human | 9140 | Details Get a Quote |
| ATG3 Knockout HEK293 Cell Line | EDJ-KQ12466 | Human | 64422 | Details Get a Quote |
| ATG5 Knockout HEK293 Cell Line | EDJ-KQ12467 | Human | 9474 | Details Get a Quote |
| ATG5 Knockout HeLa Cell Line | EDJ-KQ18163 | Human | 9474 | Details Get a Quote |
| ATG12 Knockout A-549 Cell Line | EDJ-KQ21206 | Human | 9140 | Details Get a Quote |
| ATG12 Knockout HeLa Cell Line | EDJ-KQ21208 | Human | 9140 | Details Get a Quote |
| ATG3 Knockout A-549 Cell Line | EDJ-KQ41409 | Human | 64422 | Details Get a Quote |
| ATG3 Knockout HCT 116 Cell Line | EDJ-KQ41410 | Human | 64422 | Details Get a Quote |
| ATG3 Knockout HeLa Cell Line | EDJ-KQ41411 | Human | 64422 | Details Get a Quote |
| ATG5 Knockout A-549 Cell Line | EDJ-KQ41412 | Human | 9474 | Details Get a Quote |
| ATG5 Knockout HCT 116 Cell Line | EDJ-KQ41413 | Human | 9474 | Details Get a Quote |
| ATG12 Knockout HCT 116 Cell Line | EDJ-KQ19844 | Human | 9140 | Details Get a Quote |
| ATG5 Knockout Huh-7 Cell Line | EDJ-KZ1 | Human | 9474 | Details Get a Quote |
| ATG5 Knockout NCI-H1299 Cell Line | EDJ-KZ10 | Human | 9474 | Details Get a Quote |
| ATG5 Knockout PK-15 Cell Line | EDJ-KZ100 | Pig | 100739102 | Details Get a Quote |
Displaying Records 1 To 15 Of 17 Records
Frequently Asked Questions About Atg8-family ligase activity
What is Atg8-family ligase activity?
Atg8-family ligase activity (GO:0019776) is the molecular function that covalently attaches ubiquitin-like Atg8-family modifiers to phosphatidylethanolamine or phosphatidylserine on a membrane.
What genes are involved in Atg8-family ligase activity?
Key genes include ATG7 (E1-like), ATG3 (E2-like), and ATG12, ATG5 and ATG16L1, which form the E3-like complex, as well as Atg8-family modifiers such as LC3B and GABARAP.
What is the GO ID for Atg8-family ligase activity?
The GO ID is GO:0019776, with synonyms including APG8 ligase activity, Atg8 ligase activity and Atg8-like ligase activity.
How is Atg8-family ligase activity regulated?
It is regulated by allosteric control through a switch element in the E2 enzyme Atg3 and by structural rearrangements in high-plasticity regions of Atg3. Neddylation-dependent stabilization of LC3B also influences the available modifier pool.
Is Atg8-family ligation required for phagophore growth?
Not strictly; ATG4 family proteins can drive phagophore growth independently of the LC3/GABARAP lipidation system, indicating that ligation is not the sole driver of membrane expansion.
How does Atg8-family ligase activity relate to mitophagy?
Autophagy adaptors mediate Parkin-dependent mitophagy by forming sheet-like liquid condensates, and two axes, CALCOCO2-RB1CC1 and OPTN-ATG9A, initiate PRKN-mediated mitophagy, linking ligation to mitochondrial clearance.
Which pathogens exploit Atg8-family ligation?
Mycobacterium tuberculosis exploits host autophagy and ubiquitin machinery to shape immune responses and host defense during infection.
What methods are used to study Atg8-family ligase activity?
Common methods include in vitro lipidation assays, fluorescence imaging of LC3/GABARAP puncta, western blot for LC3-II, proteomics and CRISPR knockout/rescue genetics.
Can Atg8-family ligase activity be measured in cells?
Yes, LC3-I to LC3-II conversion by western blot and imaging of membrane-associated LC3/GABARAP puncta are widely used cellular readouts of this activity.
What CRISPR models are available for studying Atg8-family ligase activity?
Knockout, point-mutation, knock-in, tagged knock-in and overexpression models of ATG3, ATG7, ATG5, ATG16L1, LC3B, GABARAP and mitophagy adaptors can be generated to dissect GO:0019776 function.
Conclusion
GO:0019776, Atg8-family ligase activity, is the enzymatic function that anchors ubiquitin-like Atg8-family modifiers to membrane lipids, a step central to autophagy and selective degradation pathways. Its mechanism depends on Atg7, Atg3 and the Atg12-Atg5-Atg16L1 complex, with allosteric and structural regulation built into the E2 enzyme. Because this activity intersects with mitophagy, infection, skin autophagy and organelle repair, it remains a high-priority target for mechanistic and translational research.
References
- 1. Xu L et al.. 2025. Neddylation modification stabilizes LC3B by antagonizing its ubiquitin-mediated degradation and promoting autophagy in skin.. Proc Natl Acad Sci U S A 122(15):e2411429122 PMID: 40208944
- 2. Nguyen TN et al.. 2021. ATG4 family proteins drive phagophore growth independently of the LC3/GABARAP lipidation system.. Mol Cell 81(9):2013-2030.e9 PMID: 33773106
- 3. Yang Z et al.. 2024. Autophagy adaptors mediate Parkin-dependent mitophagy by forming sheet-like liquid condensates.. EMBO J 43(22):5613-5634 PMID: 39420095
- 4. Shariq M et al.. 2023. The exploitation of host autophagy and ubiquitin machinery by Mycobacterium tuberculosis in shaping immune responses and host defense during infection.. Autophagy 19(1):3-23 PMID: 35000542
- 5. Oh S et al.. 2026. A role for CASM in the repair of damaged Golgi architecture.. Autophagy 22(9):2268-2286 PMID: 42115886
- 6. Qiu Y et al.. 2020. Allosteric regulation through a switch element in the autophagy E2, Atg3.. Autophagy 16(1):183-184 PMID: 31690182
- 7. Yamano K et al.. 2020. Two different axes CALCOCO2-RB1CC1 and OPTN-ATG9A initiate PRKN-mediated mitophagy.. Autophagy 16(11):2105-2107 PMID: 32892694
- 8. Popelka H et al.. 2021. Multiple structural rearrangements mediated by high-plasticity regions in Atg3 are key for efficient conjugation of Atg8 to PE during autophagy.. Autophagy 17(8):1805-1808 PMID: 34338142
