GO:0061736 engulfment of target by autophagosome: Mechanism, Genes, Functions and Research Methods
Research-grade guide for scientists and biopharma professionals
Key Takeaways
• GO:0061736 (engulfment of target by autophagosome) describes the membrane invagination process by which the autophagosomal membrane surrounds cargo destined for macroautophagic degradation.
• This step is the physical commitment point of selective autophagy, determining whether mitochondria, lipid droplets, pathogens, or protein aggregates are captured for lysosomal destruction.
• Core machinery includes ATG16L1, the ATG12-ATG5-ATG16L1 complex, LC3/GABARAP lipidation, and cargo receptors such as SQSTM1/p62 and BNIP3.
• Engulfment is regulated by nutrient sensors (mTOR), endogenous metabolites, and receptor-mediated signals that recruit selective autophagy adaptors.
• Defective engulfment contributes to cancer, metabolic dysfunction-associated steatohepatitis, cerebral ischemia/reperfusion injury, and inflammasome-driven inflammation.
• CRISPR knockout, point-mutation, knock-in, and overexpression models are essential to dissect which genes causally control autophagosomal engulfment.
Description
GO:0061736, engulfment of target by autophagosome, is a biological process defined in QuickGO as the membrane invagination process by which an autophagosomal membrane surrounds an object that will be degraded by macroautophagy. In practical terms, it is the moment when the growing phagophore bends inward and seals around a specific cargo, converting a cytosolic target into an autophagic body. This step is mechanistically distinct from autophagosome nucleation and from later autophagosome-lysosome fusion, and it is the decisive event that determines substrate selectivity in macroautophagy. Researchers study GO:0061736 because it links upstream nutrient and stress signaling to downstream degradation of organelles, lipids, and protein aggregates. Selective autophagy pathways such as mitophagy, lipophagy, and xenophagy all converge on this engulfment step. Receptor-mediated mitophagy requires cargo receptors to engage the autophagosomal membrane so that the mitochondrion is enclosed. In macrophages, ATG16L1-dependent engulfment of lipid droplets during lipophagy suppresses metabolic dysfunction-associated steatohepatitis progression. Because engulfment determines what gets degraded, its dysregulation has direct consequences for cancer cell survival, inflammatory signaling, and neuronal homeostasis. From a methods perspective, GO:0061736 is interrogated with imaging of LC3-positive structures, flux assays, and genetic perturbation of core ATG genes. The availability of real CRISPR models now allows researchers to test whether a candidate gene is required for engulfment specifically, rather than for autophagy in general.
engulfment of target by autophagosome At A Glance
| GO ID | GO:0061736 |
|---|---|
| GO term | engulfment of target by autophagosome |
| Ontology | biological_process |
| Synonym | None listed in QuickGO |
| Definition | The membrane invagination process by which an autophagosomal membrane surrounds an object that will be degraded by macroautophagy |
| Major function | Selective capture of cytosolic cargo into the autophagosome for lysosomal degradation |
| Parent process | Macroautophagy |
| Representative cargo | Mitochondria, lipid droplets, protein aggregates, intracellular pathogens |
| Key machinery | ATG16L1, ATG12-ATG5-ATG16L1 complex, LC3/GABARAP lipidation, cargo receptors |
What Is GO:0061736?
In our own words, GO:0061736 is the membrane-remodeling step in which the autophagosomal membrane invaginates and wraps around a cytosolic object, such as an organelle, a lipid droplet, a microbe, or a protein aggregate, so that the object becomes enclosed within the autophagosome and is subsequently delivered for macroautophagic degradation. It is a biological process, not a static structure, and it is defined by the act of surrounding a target rather than by the identity of the target itself.
Why Is engulfment of target by autophagosome Important in Cell Biology?
GO:0061736 matters because it is the selectivity checkpoint of macroautophagy. Upstream signals can initiate phagophore formation, but unless the membrane successfully invaginates around a target, no selective degradation occurs. This makes engulfment a focal point for understanding how cells clear damaged mitochondria, excess lipid, and aggregated proteins, and why failure of this step is linked to cancer, metabolic liver disease, ischemia/reperfusion injury, and inflammatory disorders.
• Defines cargo selectivity in macroautophagy, distinguishing selective from bulk degradation.
• Required for mitophagy, including receptor-mediated clearance of damaged mitochondria.
• Supports lipophagy, which controls lipid droplet turnover and metabolic homeostasis.
• Contributes to inflammasome regulation and inflammatory signaling.
• Implicated in cancer cell survival and therapeutic resistance through selective autophagy.
• Relevant to cerebral ischemia/reperfusion injury via SIRT3-mediated mitophagy.
• Influenced by endogenous metabolites that tune mitophagy capacity.
• A target for autophagy-tethering compounds that artificially induce targeted clearance.
• Provides a mechanistic readout for genetic screens of autophagy regulators.
• Essential for interpreting ATG gene function in disease models.
What Happens During engulfment of target by autophagosome?
Cargo recognition and receptor engagement
In simple terms: First, the cell marks the object that needs to be destroyed.
Engulfment begins when a cytosolic target is recognized by selective autophagy receptors or by receptor proteins on the cargo surface. In receptor-mediated mitophagy, mitochondrial receptors recruit the autophagic machinery to the organelle so that it can be enclosed. Endogenous metabolites can modulate this recognition step, influencing whether mitochondria are efficiently targeted for mitophagy. Without cargo recognition, the autophagosomal membrane cannot be directed to invaginate around a specific object.
ATG16L1-dependent membrane invagination
In simple terms: The autophagosome membrane then bends inward around the marked target.
The ATG12-ATG5-ATG16L1 complex acts at the expanding phagophore to promote membrane remodeling and conjugation of LC3-family proteins. Macrophage ATG16L1 expression is required for lipophagy, and its loss impairs engulfment of lipid droplets and worsens metabolic dysfunction-associated steatohepatitis progression. This step represents the core membrane invagination event that defines GO:0061736.
LC3/GABARAP lipidation and membrane anchoring
In simple terms: Small proteins are attached to the membrane so it can close around the cargo.
Lipidated LC3/GABARAP proteins anchor to the autophagosomal membrane and interact with cargo receptors, coupling recognition to enclosure. SNARE proteins later mediate fusion, but the lipidation step itself is upstream and supports the engulfment process. Selective autophagy pathways depend on this anchoring to complete cargo enclosure.
Sealing and maturation of the autophagosome
In simple terms: The membrane closes, trapping the target inside.
After invagination, the autophagosomal membrane seals to form a double-membrane vesicle containing the target. Subsequent fusion with lysosomes requires SNARE proteins, and defects in fusion are distinct from engulfment defects. Autophagy-tethering compounds can artificially drive targeted clearance, demonstrating that engulfment can be chemically induced.
Integration with metabolic and stress signaling
In simple terms: The cell decides whether to engulf based on its nutrient and stress status.
Engulfment is not constitutive; it is tuned by nutrient sensors and metabolites. Endogenous metabolites regulate mitophagy, linking metabolic state to engulfment capacity. In ischemia/reperfusion injury, SIRT3-mediated mitophagy influences neuronal survival, showing that engulfment is responsive to stress signaling. Inflammasome activity is also modulated by autophagy, tying engulfment to innate immune outcomes.
Key Genes Involved in GO:0061736 engulfment of target by autophagosome
The following genes and proteins are experimentally implicated in autophagosomal engulfment and its regulation.
| Gene | Major Role | Research Relevance |
|---|---|---|
| ATG16L1 | Core autophagy factor required for lipophagy and membrane invagination | Macrophage ATG16L1 loss impairs lipid droplet engulfment and worsens steatohepatitis |
| ATG5 | Component of ATG12-ATG5-ATG16L1 conjugation system | Essential for LC3 lipidation and engulfment |
| ATG12 | Conjugates with ATG5 to form E3-like complex | Required for autophagosomal membrane expansion |
| MAP1LC3B | Lipidated autophagosomal membrane marker | Readout for engulfment and autophagosome formation |
| GABARAP | LC3-family protein anchoring cargo receptors | Supports selective cargo enclosure |
| SQSTM1 | Selective autophagy receptor | Binds ubiquitinated cargo and LC3 for engulfment |
| BNIP3 | Mitochondrial receptor for mitophagy | Recruits autophagic machinery to mitochondria |
| NIX/BNIP3L | Mitophagy receptor | Mediates receptor-mediated mitochondrial clearance |
| FUNDC1 | Mitochondrial mitophagy receptor | Responds to hypoxia and stress for engulfment |
| SIRT3 | Mitochondrial deacetylase regulating mitophagy | Protects against cerebral ischemia/reperfusion injury |
| SNARE proteins | Mediate autophagosome-lysosome fusion | Downstream of engulfment but required for degradation |
| mTOR | Nutrient sensor inhibiting autophagy | Regulates initiation upstream of engulfment |
| AMPK | Energy sensor activating autophagy | Promotes engulfment under metabolic stress |
| ATG7 | E1-like enzyme for LC3 lipidation | Required for autophagosome membrane conjugation |
| ATG10 | E2-like enzyme for ATG12 conjugation | Supports ATG12-ATG5-ATG16L1 assembly |
| ATG3 | E2-like enzyme for LC3 lipidation | Essential for membrane anchoring |
| ATG4 | Cysteine protease processing LC3 | Regulates LC3 availability for lipidation |
| VPS34 | PI3K required for phagophore nucleation | Upstream of engulfment membrane expansion |
How Is engulfment of target by autophagosome Regulated?
Engulfment of target by autophagosome is regulated at multiple levels. Nutrient sensors such as mTOR and AMPK control the initiation of autophagy upstream of membrane invagination, and endogenous metabolites further tune mitophagy capacity. Receptor-mediated mitophagy is regulated by cargo receptors including BNIP3, NIX/BNIP3L, and FUNDC1, which respond to hypoxia and mitochondrial damage. In macrophages, ATG16L1 expression level determines lipophagic engulfment and influences metabolic liver disease progression. SNARE proteins regulate the later fusion step, and their dysfunction can phenocopy degradation defects even when engulfment is intact. Autophagy-tethering compounds can pharmacologically induce targeted engulfment, showing that this process is druggable.
engulfment of target by autophagosome and Human Disease
| Gene | Disease / Biology | Potential Experimental Model |
|---|---|---|
| ATG16L1 | Metabolic dysfunction-associated steatohepatitis | Macrophage-specific knockout in mice |
| SIRT3 | Cerebral ischemia/reperfusion injury | Neuronal overexpression or knockout in ischemia models |
| BNIP3 | Mitophagy-related cancer and hypoxia response | Cancer cell lines with BNIP3 knockout |
| SQSTM1 | Protein aggregate diseases and cancer | Knockout cell lines with aggregate clearance assays |
| SNARE proteins | Autophagic degradation defects | Point-mutation models of fusion machinery |
Cancer
Selective autophagy supports tumor cell survival under stress by removing damaged organelles and providing metabolic substrates. Engulfment of target by autophagosome is therefore a potential therapeutic vulnerability, and understanding which cargo is engulfed in specific tumors can guide autophagy inhibition strategies.
Metabolic dysfunction-associated steatohepatitis
Macrophage ATG16L1-dependent lipophagy requires engulfment of lipid droplets by autophagosomes. Loss of ATG16L1 impairs this engulfment and accelerates metabolic dysfunction-associated steatohepatitis progression, linking GO:0061736 to liver disease.
Cerebral ischemia/reperfusion injury
SIRT3-mediated mitophagy protects neurons during ischemia/reperfusion injury, and this protection depends on efficient engulfment of damaged mitochondria by autophagosomes. Compounds that target this pathway are being explored for neuroprotection.
Inflammatory and inflammasome-related disorders
Autophagy regulates inflammasome activity, and engulfment of damaged organelles or pathogens can limit inflammatory signaling. Dysregulated engulfment may therefore contribute to inflammasome-driven pathology.
From engulfment of target by autophagosome-Related Genes to Experimental Models
| Research Question | Suitable Model |
|---|---|
| Is ATG16L1 required for lipid droplet engulfment? | Macrophage ATG16L1 knockout |
| Does SIRT3 mediate mitophagy in neurons? | SIRT3 knockout or overexpression in ischemia models |
| Which receptor drives mitochondrial engulfment? | BNIP3/NIX/FUNDC1 knockout cell lines |
| Can a compound induce targeted engulfment? | Autophagy-tethering compound treatment in cells |
| Does a SNARE mutation block degradation after engulfment? | Point-mutation knock-in of SNARE genes |
| Is a candidate gene causally required for engulfment? | CRISPR knockout with LC3 flux imaging |
How to Study the engulfment of target by autophagosome Process
| Method | What It Measures | Typical Application |
|---|---|---|
| LC3 immunofluorescence | Autophagosome number and cargo co-localization | Engulfment visualization |
| Mitophagy flux assay | Mitochondrial delivery to lysosomes | Receptor-mediated mitophagy |
| Lipophagy assay | Lipid droplet co-localization with LC3 | Macrophage ATG16L1 studies |
| CRISPR knockout | Causal requirement of a gene | Candidate gene validation |
| Autophagy-tethering compound assay | Induced targeted clearance | Therapeutic screening |
| SNARE fusion assay | Autophagosome-lysosome fusion | Distinguishing engulfment from fusion |
| Metabolomics | Endogenous metabolite levels | Mitophagy regulation |
| Inflammasome readout | IL-1beta activation | Autophagy-inflammation crosstalk |
Imaging-based engulfment assays
Fluorescence microscopy of LC3-positive structures and cargo markers allows direct visualization of autophagosomal engulfment. Co-localization of mitochondria or lipid droplets with LC3 puncta indicates engulfment, and time-lapse imaging can capture membrane invagination.
Autophagic flux measurements
LC3 turnover assays in the presence and absence of lysosomal inhibitors distinguish engulfment from downstream degradation. SNARE-dependent fusion steps can be separated from engulfment using fusion-defective mutants.
Genetic perturbation and CRISPR screens
CRISPR knockout and knock-in models enable causal testing of candidate genes in engulfment. Library screening can identify novel regulators of selective autophagy and mitophagy.
Metabolite and stress profiling
Endogenous metabolites modulate mitophagy, so metabolomic profiling combined with engulfment assays can reveal how metabolic state controls GO:0061736. Inflammasome readouts can link engulfment to inflammatory outcomes.
How CRISPR Can Be Used to Study GO:0061736 engulfment of target by autophagosome
Knockout
CRISPR knockout of ATG16L1, ATG5, or ATG7 abolishes autophagosomal engulfment and provides a clean negative control for engulfment assays. Macrophage ATG16L1 knockout models have been used to demonstrate the requirement for lipophagy in steatohepatitis.
Point Mutation
Point mutations in SNARE proteins or LC3-family proteins can selectively disrupt membrane fusion or lipidation without eliminating protein expression, allowing researchers to separate engulfment from downstream degradation.
Knock-in
Knock-in of fluorescent tags such as GFP-LC3 or mCherry-LC3 enables live imaging of autophagosomal membranes during engulfment. Tagged cargo receptors can also be knocked in to track selective engulfment in real time.
Overexpression
Overexpression of mitophagy receptors such as BNIP3 or FUNDC1 can drive enhanced mitochondrial engulfment, while overexpression of SIRT3 has been used to study protection against ischemia/reperfusion injury.
How EDITGENE Supports engulfment of target by autophagosome Research
Researchers studying engulfment of target by autophagosome-related genes often need to determine whether a candidate gene is causally involved in membrane invagination, cargo recognition, or downstream degradation. EDITGENE provides the CRISPR models and screening services required to make those distinctions with publication-grade rigor.
Contact EDITGENE today to design your custom CRISPR model for engulfment of target by autophagosome research.
Frequently Asked Questions About engulfment of target by autophagosome
What is GO:0061736 engulfment of target by autophagosome?
GO:0061736 is the biological process in which the autophagosomal membrane invaginates and surrounds a cytosolic target so that it can be degraded by macroautophagy.
What genes are involved in engulfment of target by autophagosome?
Key genes include ATG16L1, ATG5, ATG12, MAP1LC3B, GABARAP, SQSTM1, BNIP3, NIX/BNIP3L, FUNDC1, and SIRT3.
How is engulfment of target by autophagosome different from autophagosome-lysosome fusion?
Engulfment is the membrane invagination step that captures cargo, while fusion is the later SNARE-dependent step that delivers the autophagosome to the lysosome.
Why is ATG16L1 important for autophagosomal engulfment?
ATG16L1 is part of the ATG12-ATG5-ATG16L1 complex that promotes LC3 lipidation and membrane invagination; its loss impairs lipophagy in macrophages.
What diseases are linked to defective engulfment of target by autophagosome?
Defects are linked to cancer, metabolic dysfunction-associated steatohepatitis, cerebral ischemia/reperfusion injury, and inflammasome-related inflammation.
How do researchers measure engulfment of target by autophagosome?
Common methods include LC3 immunofluorescence, mitophagy flux assays, lipophagy assays, and CRISPR perturbation combined with imaging.
Can engulfment of target by autophagosome be induced pharmacologically?
Yes, autophagy-tethering compounds can induce targeted clearance of mitochondria, demonstrating that engulfment can be chemically stimulated.
What is the role of endogenous metabolites in mitophagy engulfment?
Endogenous metabolites modulate mitophagy capacity and influence whether mitochondria are efficiently engulfed by autophagosomes.
Which CRISPR model is best for studying engulfment of target by autophagosome?
Knockout models are best for testing causal requirement, while knock-in of tagged LC3 or cargo receptors is best for live imaging.
How does SIRT3 affect autophagosomal engulfment in neurons?
SIRT3-mediated mitophagy protects against cerebral ischemia/reperfusion injury, indicating that SIRT3 supports engulfment of damaged mitochondria.
Conclusion
GO:0061736, engulfment of target by autophagosome, is the selectivity-defining step of macroautophagy. It integrates cargo recognition, ATG16L1-dependent membrane invagination, LC3 lipidation, and sealing to determine which cytosolic objects are degraded. Its dysfunction is implicated in cancer, metabolic liver disease, neuronal injury, and inflammation. Because engulfment is genetically tractable, CRISPR knockout, point-mutation, knock-in, and overexpression models are essential tools for dissecting its mechanism and for identifying therapeutic targets. EDITGENE provides these models and screening services to accelerate research on this critical autophagy step.
References
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