GO:0034271 phosphatidylinositol 3-kinase complex, class III, type I: Components, Assembly and Research Methods, Genes, Functions and Research Methods
Research-grade guide for scientists and biopharma professionals
Key Takeaways
• GO:0034271 describes the autophagy-specific class III phosphatidylinositol 3-kinase (PtdIns3K) complex I, which in budding yeast consists of Vps30p, Vps34p, Apg14p and Vps15p.
• This complex is essential for the initiation of autophagy, a conserved lysosomal degradation pathway that maintains cellular homeostasis [1,2].
• The catalytic subunit Vps34 (PIK3C3 in mammals) phosphorylates phosphatidylinositol to generate phosphatidylinositol 3-phosphate (PI3P), a lipid mark that recruits downstream autophagy effectors [1,7].
• Dysregulation of the complex is linked to human diseases including cancer, inflammatory disorders, and liver disease [2,4,7].
• Key regulatory inputs include nutrient-sensing pathways such as mTOR, which controls complex assembly and activity [1,2].
• CRISPR-based knockout, point mutation, knock-in, and overexpression models are powerful tools to dissect the function of individual subunits in autophagy and disease [3,5,8].
Description
The phosphatidylinositol 3-kinase complex, class III, type I (GO:0034271) is a multiprotein complex that plays a central role in the initiation of autophagy, a catabolic process that delivers cytoplasmic material to lysosomes for degradation and recycling. In budding yeast, this complex is composed of Vps30p, Vps34p, Apg14p and Vps15p, and it is specifically dedicated to autophagy. The complex is also known as the autophagy-specific PtdIns3K complex or PtdIns-3-kinase complex I. Its primary function is to phosphorylate phosphatidylinositol at the third position of the inositol ring to produce phosphatidylinositol 3-phosphate (PI3P), a lipid second messenger that recruits proteins containing PI3P-binding domains to the phagophore assembly site, thereby driving autophagosome formation [1,7]. Research on this complex has expanded rapidly because autophagy is implicated in a wide range of physiological and pathological processes, including cancer, neurodegeneration, liver disease, and immune responses [2,4,7]. The complex integrates nutrient and stress signals to control the magnitude of autophagic flux, and its subunits are subject to multiple layers of regulation, including post-translational modifications such as acetylation and S-palmitoylation [1,3,8]. Understanding the structure, assembly, and regulation of GO:0034271 is therefore critical for deciphering how cells maintain homeostasis and how autophagy contributes to disease. This article provides a comprehensive overview of GO:0034271, covering its definition, composition, molecular mechanism, key genes, regulation, disease relevance, and the experimental methods used to study it. It is intended for researchers seeking a concise, evidence-based resource that can guide experimental design and interpretation.
phosphatidylinositol 3-kinase complex, class III, type I At A Glance
| GO ID | GO:0034271 |
|---|---|
| GO term | phosphatidylinositol 3-kinase complex, class III, type I |
| Ontology | cellular_component |
| Synonym | autophagy-specific phosphatidylinositol 3-kinase (PtdIns3K) complex; phosphatidylinositol 3-kinase complex I; PtdIns-3-kinase complex I |
| Major function | Autophagy initiation; generation of phosphatidylinositol 3-phosphate (PI3P) at the phagophore assembly site |
| Subunits (yeast) | Vps30p, Vps34p, Apg14p, Vps15p |
| Subunits (mammalian) | Beclin-1 (BECN1), VPS34 (PIK3C3), ATG14, VPS15 (PIK3R4), and additional factors such as NRBF2 |
| Catalytic activity | Phosphatidylinositol 3-kinase activity (EC 2.7.1.137) |
| Localization | Cytosol; phagophore assembly site (PAS); autophagosome membrane |
What Is GO:0034271?
GO:0034271 refers to a class III phosphatidylinositol 3-kinase complex that is specifically involved in autophagy. In budding yeast, this complex consists of four subunits: Vps30p, Vps34p, Apg14p, and Vps15p. It is also known as the autophagy-specific PtdIns3K complex or PtdIns-3-kinase complex I. The complex catalyzes the phosphorylation of phosphatidylinositol to generate phosphatidylinositol 3-phosphate (PI3P), which is essential for autophagosome nucleation and expansion.
Why Is phosphatidylinositol 3-kinase complex, class III, type I Important in Cell Biology?
GO:0034271 is critically important because it serves as the molecular switch for autophagy initiation, a process that is fundamental to cellular quality control, stress adaptation, and survival. Dysregulation of this complex has been directly linked to human pathologies including cancer, inflammatory bowel disease, liver steatosis, and neurodegenerative disorders [2,4,7]. Moreover, the complex is a hub for signal integration, receiving inputs from nutrient-sensing pathways such as mTOR and from post-translational modifications that fine-tune its activity [1,3,8]. Understanding its function provides insights into basic cell biology and offers potential therapeutic targets for diseases where autophagy is perturbed.
• Autophagy initiation: The complex generates PI3P, which is required for the recruitment of downstream effectors like ATG18/WIPI and for autophagosome formation.
• Cancer: Altered expression of subunits such as BECN1 and PIK3C3 is observed in various cancers, and the complex can influence tumor progression.
• Inflammatory diseases: NRBF2, a subunit of the complex, is required for apoptotic cell clearance and restricts intestinal inflammation.
• Liver disease: Autophagy dysfunction, including impaired complex activity, contributes to lipid droplet accumulation and liver steatosis.
• Neurodegeneration: Defective autophagy is a hallmark of neurodegenerative diseases, and the complex is a key regulator of neuronal proteostasis.
• Immunity: The complex participates in unconventional secretion of HMGB1 in keratinocytes, linking autophagy to psoriatic skin inflammation.
• Post-translational regulation: Acetylation and S-palmitoylation of complex components modulate autophagy flux [1,3,8].
• Therapeutic target: Small molecules that modulate the complex are being explored for autophagy-related diseases.
• Model organism insights: Yeast genetics has been instrumental in defining the core components and their functions.
• CRISPR screening: Genome-wide screens can identify novel regulators of the complex and autophagy [3,5].
Structure and Composition of phosphatidylinositol 3-kinase complex, class III, type I
Core subunits and stoichiometry
In simple terms: The complex is made of four main proteins that work together like a tiny machine.
In budding yeast, the autophagy-specific PtdIns3K complex I consists of Vps34p (the catalytic subunit), Vps15p (a regulatory subunit with kinase-like domain), Vps30p (also known as Atg6), and Apg14p (also known as Atg14). Vps34p is the only subunit with lipid kinase activity, while the others provide structural support, membrane targeting, and regulation. In mammals, the orthologous complex includes PIK3C3 (VPS34), PIK3R4 (VPS15), BECN1 (Beclin-1), and ATG14, and may associate with additional factors such as NRBF2.
Assembly and membrane recruitment
In simple terms: The complex is assembled in the cytosol and then moves to a specific location on the membrane where autophagy begins.
Assembly of the complex is regulated by nutrient status and stress signals. The Vps15p-Vps34p subcomplex forms a stable core, and binding of Vps30p and Apg14p is required for autophagy-specific function. The complex is recruited to the phagophore assembly site (PAS) through interactions with membrane lipids and proteins, including Atg9-containing vesicles. In mammals, ATG14 targets the complex to the PAS, while BECN1 mediates interactions with regulatory proteins such as AMBRA1 and BCL-2.
Structural features and domains
In simple terms: Each subunit has specific domains that allow it to interact with others and with lipids.
Vps34p contains a C2 domain, a helical domain, and a catalytic kinase domain. Vps15p has a protein kinase-like domain and WD40 repeats that mediate protein-protein interactions. Vps30p/BECN1 contains a BH3 domain, a coiled-coil domain, and an evolutionarily conserved domain (ECD) that binds to Vps34p. Apg14p/ATG14 contains a coiled-coil domain and a cysteine-rich domain that targets the complex to the PAS.
Post-translational modifications
In simple terms: Small chemical tags can be added to the complex subunits to change how they work.
Acetylation of autophagy-related proteins, including components of the PtdIns3K complex, regulates autophagy in response to metabolic cues. S-palmitoylation of ATG16L1 and ATG9A, which are downstream of the complex, also modulates autophagy initiation and autophagosome formation [3,8]. These modifications can affect protein stability, membrane association, and interactions, thereby fine-tuning complex activity.
Key Genes Involved in GO:0034271 phosphatidylinositol 3-kinase complex, class III, type I
The following genes encode the core subunits and key regulators of the phosphatidylinositol 3-kinase complex, class III, type I, and are frequently studied in autophagy research.
| Gene | Major Role | Research Relevance |
|---|---|---|
| VPS34 (PIK3C3) | Catalytic subunit; phosphorylates phosphatidylinositol to generate PI3P | Central to autophagy initiation; target for autophagy modulators |
| VPS15 (PIK3R4) | Regulatory subunit; stabilizes VPS34 and targets complex to membranes | Essential for complex assembly and function |
| VPS30 (BECN1) | Scaffold subunit; interacts with VPS34 and ATG14; regulates complex activity | Implicated in cancer and neurodegeneration [1,4] |
| APG14 (ATG14) | Autophagy-specific subunit; targets complex to PAS | Determines autophagy specificity |
| NRBF2 | Accessory subunit in mammals; modulates complex activity and apoptotic cell clearance | Linked to intestinal inflammation |
| ATG16L1 | Downstream effector; S-palmitoylation facilitates LC3 lipidation | Inflammatory bowel disease risk gene |
| ATG9A | Transmembrane protein; trafficking regulated by S-palmitoylation | Autophagy initiation and membrane supply |
| HMGB1 | Nuclear protein; secreted via autophagy-based unconventional secretion | Psoriatic skin inflammation |
| MTOR | Kinase; inhibits autophagy by phosphorylating complex components | Nutrient sensing and autophagy regulation |
| AMBRA1 | Positive regulator; promotes complex assembly and activity | Autophagy and development |
| BCL-2 | Anti-apoptotic protein; binds BECN1 to inhibit autophagy | Crosstalk between apoptosis and autophagy |
| UVRAG | Promotes complex activity and autophagosome maturation | Tumor suppressor candidate |
| ATG14L | Mammalian ortholog of Apg14; essential for autophagy | Autophagy-specific targeting |
| WIPI1/2 | PI3P-binding proteins; downstream effectors | Autophagosome formation |
| ZDHHC7 | Palmitoyltransferase; modifies ATG16L1 | Regulates LC3 lipidation |
| VPS34 complex I | Autophagy-specific complex | Core machinery for autophagy initiation |
How Is phosphatidylinositol 3-kinase complex, class III, type I Regulated?
The activity of the phosphatidylinositol 3-kinase complex, class III, type I is tightly regulated by nutrient and stress signals. Under nutrient-rich conditions, mTORC1 phosphorylates components of the complex, including ATG14, to inhibit autophagy initiation. Conversely, starvation or mTOR inhibition leads to dephosphorylation and activation of the complex. Additional regulation occurs through post-translational modifications such as acetylation, which can affect protein stability and interactions. S-palmitoylation of downstream effectors like ATG16L1 and ATG9A also modulates autophagy flux [3,8]. Furthermore, interaction with proteins such as AMBRA1, BCL-2, and NRBF2 can either promote or inhibit complex activity depending on cellular context [1,7].
phosphatidylinositol 3-kinase complex, class III, type I and Human Disease
| Gene | Disease / Biology | Potential Experimental Model |
|---|---|---|
| BECN1 | Cancer (tumor suppressor); autophagy regulation | BECN1 knockout and knock-in cell lines; xenograft models |
| NRBF2 | Intestinal inflammation; apoptotic cell clearance | NRBF2 knockout mice; intestinal organoids |
| PIK3C3 | Cancer; autophagy initiation | PIK3C3 conditional knockout; CRISPR point mutations |
| ATG14 | Neurodegeneration; autophagy specificity | ATG14 knockout neurons; iPSC-derived models |
| HMGB1 | Psoriasis; inflammation | Keratinocyte-specific knockout; overexpression models |
Cancer
Dysregulation of autophagy, often through altered expression or mutation of PtdIns3K complex subunits, is observed in many cancers. BECN1 is a haploinsufficient tumor suppressor, and its loss impairs autophagy and promotes tumorigenesis. Conversely, in some contexts, autophagy supports tumor cell survival under stress, making the complex a potential therapeutic target.
Inflammatory and immune disorders
NRBF2, a subunit of the complex, is required for apoptotic cell clearance and restricts intestinal inflammation. Defects in this process can lead to chronic inflammation and autoimmune responses. Additionally, autophagy-based unconventional secretion of HMGB1 by keratinocytes plays a pivotal role in psoriatic skin inflammation, linking the complex to inflammatory skin diseases.
Liver disease
Autophagy dysfunction contributes to lipid droplet accumulation and liver steatosis. The PtdIns3K complex is essential for lipophagy, the autophagic degradation of lipid droplets, and its impairment exacerbates liver disease progression [2,5].
Neurodegeneration
Defective autophagy is a common feature of neurodegenerative diseases such as Alzheimer's and Parkinson's. The PtdIns3K complex is critical for neuronal proteostasis, and its dysfunction can lead to the accumulation of toxic protein aggregates.
From phosphatidylinositol 3-kinase complex, class III, type I-Related Genes to Experimental Models
| Research Question | Suitable Model |
|---|---|
| Does loss of VPS34 abolish autophagy? | VPS34 knockout cell lines (CRISPR) |
| How does a disease-associated point mutation affect complex activity? | Point mutation knock-in via CRISPR |
| Can a tagged subunit be used to track complex localization? | Knock-in of fluorescent tag (e.g., GFP) |
| Does overexpression of BECN1 enhance autophagy? | BECN1 overexpression stable cell lines |
| What genes regulate the complex in a genome-wide manner? | CRISPR library screening [3,5] |
| How does NRBF2 contribute to intestinal homeostasis? | NRBF2 knockout mouse models |
How to Study the phosphatidylinositol 3-kinase complex, class III, type I Process
| Method | What It Measures | Typical Application |
|---|---|---|
| CRISPR knockout screening | Gene essentiality for autophagy | Identify novel regulators of the complex |
| AP-MS | Protein-protein interactions | Define complex composition and dynamics |
| Live-cell imaging | Complex localization and autophagosome formation | Track autophagy initiation |
| Lipid kinase assay | PI3P production | Measure catalytic activity of VPS34 |
| Western blot | LC3 lipidation and protein levels | Monitor autophagy flux |
| qPCR/RNA-seq | Gene expression changes | Assess transcriptional regulation |
| Proximity labeling (BioID) | Interactome in living cells | Capture transient interactions |
| CRISPR point mutation knock-in | Effect of specific mutations | Model disease-associated variants |
CRISPR-based genetic screens
Genome-wide CRISPR knockout or activation screens can identify novel regulators of the PtdIns3K complex and autophagy. These screens typically use reporters such as GFP-LC3 to monitor autophagosome formation and can uncover genes that modulate complex activity [3,5].
Proteomics and interactomics
Affinity purification coupled with mass spectrometry (AP-MS) can define the composition of the complex and identify dynamic interactions under different conditions. Proximity labeling approaches such as BioID can capture transient interactions in living cells.
Imaging and live-cell analysis
Fluorescence microscopy of tagged subunits (e.g., GFP-ATG14) allows visualization of complex localization at the PAS. Live-cell imaging can track autophagosome formation and flux in real time.
Biochemical assays for PI3P production
In vitro lipid kinase assays using recombinant complex or immunoprecipitated material measure the conversion of phosphatidylinositol to PI3P. PI3P levels can also be monitored in cells using PI3P-binding probes such as GFP-2xFYVE.
How CRISPR Can Be Used to Study GO:0034271 phosphatidylinositol 3-kinase complex, class III, type I
Knockout
CRISPR knockout of core subunits such as PIK3C3, BECN1, or ATG14 completely abolishes autophagy initiation, providing a clean background to study downstream effects. These models are invaluable for confirming the essential role of the complex in autophagy and for identifying compensatory pathways.
Point Mutation
Introducing specific point mutations (e.g., in the catalytic domain of VPS34 or in disease-associated residues of BECN1) allows researchers to dissect the contribution of individual amino acids to complex assembly, kinase activity, and autophagy. Such models can mimic human mutations and reveal genotype-phenotype relationships.
Knock-in
Knock-in of epitope tags (e.g., FLAG, HA) or fluorescent proteins (e.g., GFP) at endogenous loci enables precise tracking of subunit expression, localization, and interactions without overexpression artifacts. This approach is particularly useful for studying dynamic complex assembly at the PAS.
Overexpression
Overexpression of wild-type or mutant subunits can be used to test gain-of-function effects, such as enhanced autophagy or dominant-negative inhibition. For example, overexpressing a kinase-dead VPS34 mutant can sequester binding partners and block autophagy.
How EDITGENE Supports phosphatidylinositol 3-kinase complex, class III, type I Research
Researchers studying phosphatidylinositol 3-kinase complex, class III, type I-related genes often need to determine whether a candidate gene is causally involved in autophagy regulation, disease progression, or drug response. EDITGENE provides a comprehensive suite of CRISPR-based services to accelerate this discovery process, from gene knockout to precise point mutations and library screening.
Contact EDITGENE today to design your custom CRISPR model for phosphatidylinositol 3-kinase complex, class III, type I research.
Frequently Asked Questions About phosphatidylinositol 3-kinase complex, class III, type I
What is GO:0034271?
GO:0034271 is the Gene Ontology term for the phosphatidylinositol 3-kinase complex, class III, type I, an autophagy-specific lipid kinase complex that generates PI3P to initiate autophagosome formation.
What genes are involved in phosphatidylinositol 3-kinase complex, class III, type I?
In yeast, the complex includes VPS30, VPS34, APG14, and VPS15. In mammals, the core subunits are BECN1, PIK3C3, ATG14, and PIK3R4, with accessory proteins such as NRBF2 [1,7].
What is the function of the class III PI3K complex?
It phosphorylates phosphatidylinositol to produce PI3P, which recruits downstream effectors to the phagophore assembly site, thereby driving autophagy initiation.
How is the class III PI3K complex regulated?
It is regulated by nutrient signals via mTOR, by post-translational modifications such as acetylation and S-palmitoylation, and by interacting proteins like AMBRA1 and BCL-2 [1,3,8].
What diseases are associated with the class III PI3K complex?
Dysregulation is linked to cancer, inflammatory bowel disease, liver steatosis, and neurodegenerative disorders [2,4,7].
What is the difference between class III PI3K complex I and II?
Complex I is autophagy-specific and contains ATG14, while complex II contains UVRAG and functions in endosomal trafficking and autophagosome maturation.
How can I study the class III PI3K complex using CRISPR?
CRISPR knockout, point mutation knock-in, and tagged knock-in cell lines can be used to dissect subunit function, localization, and disease-associated mutations [3,8].
What is the role of VPS34 in autophagy?
VPS34 is the catalytic subunit that produces PI3P, which is essential for autophagosome nucleation and expansion.
Is BECN1 a tumor suppressor?
BECN1 is considered a haploinsufficient tumor suppressor, and its loss impairs autophagy and promotes tumorigenesis in some contexts.
What experimental models are available for studying the class III PI3K complex?
Models include CRISPR knockout cell lines, point mutation knock-ins, tagged knock-ins, overexpression lines, and genome-wide CRISPR screens [3,5,8].
Conclusion
The phosphatidylinositol 3-kinase complex, class III, type I (GO:0034271) is a master regulator of autophagy initiation, with critical roles in cellular homeostasis and human disease. Its core subunits and regulatory mechanisms are conserved from yeast to mammals, making it a tractable target for genetic and pharmacological studies. Advances in CRISPR technology now allow precise manipulation of complex components, enabling researchers to dissect their functions in health and disease. Continued investigation of this complex promises to yield new insights into autophagy-related pathologies and potential therapeutic strategies.
References
- 1. Xu Y et al.. 2023. Acetylation in the regulation of autophagy.. Autophagy 19(2):379-387 PMID: 35435793
- 2. Filali-Mouncef Y et al.. 2022. The ménage à trois of autophagy, lipid droplets and liver disease.. Autophagy 18(1):50-72 PMID: 33794741
- 3. Wei F et al.. 2024. ZDHHC7-mediated S-palmitoylation of ATG16L1 facilitates LC3 lipidation and autophagosome formation.. Autophagy 20(12):2719-2737 PMID: 39087410
- 4. Devis-Jauregui L et al.. 2021. Autophagy in the physiological endometrium and cancer.. Autophagy 17(5):1077-1095 PMID: 32401642
- 5. Zhao R et al.. 2026. Mammalian lipophagy: process and function.. Autophagy 22(6):1151-1170 PMID: 41681129
- 6. Wang Z et al.. 2021. Autophagy-based unconventional secretion of HMGB1 by keratinocytes plays a pivotal role in psoriatic skin inflammation.. Autophagy 17(2):529-552 PMID: 32019420
- 7. Wu MY et al.. 2021. PI3KC3 complex subunit NRBF2 is required for apoptotic cell clearance to restrict intestinal inflammation.. Autophagy 17(5):1096-1111 PMID: 32160108
- 8. Xia F et al.. 2025. S-palmitoylation coordinates the trafficking of ATG9A to mediate autophagy initiation.. Autophagy 21(11):2422-2442 PMID: 40394978
