GO:1990050 phosphatidic acid transfer activity: Mechanism, Genes and Research Methods
Research-grade guide for scientists and biopharma professionals
Key Takeaways
• GO:1990050 phosphatidic acid transfer activity describes the removal of phosphatidic acid (PA) from a membrane, its transport through the aqueous phase protected in a hydrophobic pocket, and its delivery to an acceptor membrane or lipid particle.
• This activity is essential for maintaining lipid asymmetry and facilitating communication between organelles, particularly at membrane contact sites such as ER–PM and ER–mitochondria junctions.
• Key proteins mediating PA transfer include RMDN3/PTPIP51, Nir2, Osh6, Ist2, and TMEM16F, which often couple PA transfer to other lipid transport or scramblase activities.
• PA transfer activity is implicated in diverse physiological and pathological processes, including apoptosis, neurogenesis, sickle cell disease, and cholesterol trafficking.
• Experimental approaches to study PA transfer include biochemical transfer assays, fluorescence-based lipid transport imaging, and CRISPR-based genetic screens targeting candidate genes.
• Dysregulation of PA transfer contributes to disease; for example, targeting PIEZO1–TMEM16F coupling can mitigate sickle cell disease complications, highlighting therapeutic potential.
Description
Phosphatidic acid (PA) is a key phospholipid involved in membrane biogenesis, signaling, and organelle communication. The transfer of PA between membranes is a fundamental process that ensures proper lipid distribution and cellular homeostasis. GO:1990050, phosphatidic acid transfer activity, defines the molecular function responsible for moving PA from a donor membrane to an acceptor membrane through the aqueous phase, with the lipid protected in a hydrophobic pocket. This activity is distinct from simple diffusion or vesicular transport and is often mediated by specialized lipid transfer proteins at membrane contact sites. Understanding this activity is crucial for researchers studying lipid metabolism, membrane dynamics, and related diseases. Recent studies have identified several proteins that exhibit PA transfer activity, including RMDN3/PTPIP51, Nir2, Osh6, and Ist2, which are localized to ER–mitochondria and ER–plasma membrane contact sites. These proteins not only transfer PA but also coordinate with other lipid transfer events, such as phosphatidylserine and cholesterol transport, to maintain lipid homeostasis. The importance of PA transfer extends to apoptosis, where lipid scrambling and PA exposure facilitate the clearance of apoptotic cells. Moreover, PA transfer is linked to systemic effects, as blood factors released during exercise can enhance neurogenesis and cognition in aged animals, potentially involving lipid-mediated signaling. In sickle cell disease, targeting the PIEZO1–TMEM16F coupling, which involves PA transfer activity, has emerged as a therapeutic strategy to mitigate complications. This article provides a comprehensive overview of GO:1990050, covering its definition, mechanism, key genes, research methods, and relevance to human disease.
phosphatidic acid transfer activity At A Glance
| GO ID | GO:1990050 |
|---|---|
| GO term | phosphatidic acid transfer activity |
| Ontology | molecular_function |
| Synonym | intermembrane PA transfer activity; intermembrane phosphatidic acid transfer activity; phosphatidic acid carrier activity; phosphatidic acid transporter activity |
| Definition | Removes a phosphatidic acid from a membrane or a monolayer lipid particle, transports it through the aqueous phase while protected in a hydrophobic pocket, and brings it to an acceptor membrane or lipid particle. |
| Major function | Mediates the transfer of phosphatidic acid between membranes, facilitating lipid homeostasis and membrane contact site communication. |
| Related proteins | RMDN3/PTPIP51, Nir2, Osh6, Ist2, TMEM16F, NPC2 |
| Cellular context | Membrane contact sites (ER–mitochondria, ER–plasma membrane), lipid particles, and membranes. |
| Disease relevance | Sickle cell disease, apoptosis, cholesterol trafficking disorders, and neurogenesis. |
What Is GO:1990050?
Phosphatidic acid transfer activity (GO:1990050) is a molecular function that removes phosphatidic acid from a membrane or monolayer lipid particle, transports it through the aqueous phase while protected in a hydrophobic pocket, and delivers it to an acceptor membrane or lipid particle. Phosphatidic acid is a glycophospholipid with a saturated fatty acid at carbon-1, an unsaturated fatty acid at carbon-2, and a phosphate group at carbon-3. This activity is synonymous with intermembrane PA transfer activity, phosphatidic acid carrier activity, and phosphatidic acid transporter activity.
Why Is phosphatidic acid transfer activity Important in Cell Biology?
Phosphatidic acid transfer activity is critical for maintaining the unique lipid composition of cellular membranes and for facilitating inter-organelle communication. By moving PA between membranes, this activity influences membrane curvature, lipid signaling, and the recruitment of effector proteins. Dysregulation of PA transfer has been linked to a range of pathologies, including sickle cell disease, where targeting the PIEZO1–TMEM16F coupling can mitigate complications, and apoptosis, where PA exposure on the cell surface signals for clearance. Moreover, PA transfer is involved in systemic processes such as exercise-induced neurogenesis and cognition, suggesting broad physiological relevance. Understanding the molecular players and regulatory mechanisms of PA transfer is therefore essential for both basic cell biology and therapeutic development.
• Maintains lipid asymmetry and membrane integrity by redistributing PA between organelles.
• Facilitates membrane contact site function, enabling communication between ER, mitochondria, and plasma membrane.
• Regulates apoptosis by exposing PA on the outer leaflet for phagocytic recognition.
• Contributes to cholesterol trafficking and sphingomyelinase regulation.
• Modulates neurogenesis and cognitive function in response to exercise-induced blood factors.
• Involved in sickle cell disease pathophysiology through PIEZO1–TMEM16F coupling.
• Provides a target for therapeutic intervention in lipid-related disorders.
• Essential for understanding non-vesicular lipid transport mechanisms.
• Links lipid metabolism to cellular signaling and organelle dynamics.
• Offers opportunities for CRISPR-based screens to identify novel regulators.
What Happens During phosphatidic acid transfer activity?
Recognition and Extraction of Phosphatidic Acid
In simple terms: The transfer protein finds and picks up a PA molecule from a membrane.
The first step in PA transfer involves the recognition of phosphatidic acid within a donor membrane. Proteins with PA transfer activity, such as RMDN3/PTPIP51, possess a hydrophobic pocket that accommodates the acyl chains of PA, allowing extraction from the lipid bilayer. This process is often regulated by the local lipid environment and may require conformational changes in the transfer protein. For example, MITOL regulates the PA-binding activity of RMDN3/PTPIP51, suggesting that post-translational modifications can modulate substrate recognition.
Transport Through the Aqueous Phase
In simple terms: The protein carries the PA molecule through the water-based cytoplasm, shielding it from water.
Once extracted, PA is transported through the aqueous phase while protected within a hydrophobic pocket of the transfer protein. This step prevents the hydrophobic lipid from aggregating or being exposed to the aqueous environment. Structural studies of Nir2 reveal a PA-sensing mechanism at ER–PM contact sites, where the protein undergoes conformational changes to shuttle PA between membranes. Similarly, Osh6 and its partner Ist2 facilitate lipid transfer by tethering membranes and providing a shielded environment for PA.
Delivery to Acceptor Membrane
In simple terms: The protein releases the PA into the target membrane.
The final step is the delivery of PA to an acceptor membrane or lipid particle. This process is often coupled to the transfer of other lipids in the opposite direction, maintaining lipid balance. For instance, Osh6 transfers phosphatidylserine in exchange for PA, a counter-transport mechanism that requires Ist2's scramblase activity. In the context of cholesterol trafficking, acid sphingomyelinase activity facilitates cholesterol transfer by NPC2, highlighting the interconnectedness of lipid transfer pathways. The delivery step is crucial for maintaining membrane lipid composition and for signaling events that depend on PA localization.
Regulation by Membrane Contact Sites
In simple terms: The transfer happens at specific contact points between organelles.
PA transfer activity is spatially organized at membrane contact sites, where the ER and other organelles come into close apposition. Proteins like RMDN3/PTPIP51 localize to ER–mitochondria contact sites and regulate PA transfer, influencing mitochondrial function and apoptosis. Nir2 functions at ER–PM contact sites, where it senses PA and coordinates lipid exchange. These contact sites provide a platform for efficient lipid transfer and are dynamically regulated in response to cellular cues.
Non-Protein-Mediated Transfer
In simple terms: PA can also move between membranes without a protein helper, but less efficiently.
Although protein-mediated transfer is the primary mechanism, non-protein-mediated transfer of PA between microsomal and mitochondrial membranes has been demonstrated in vitro. This process likely occurs through transient membrane hemifusion or lipid diffusion, but it is slower and less specific than protein-mediated transfer. The existence of non-protein-mediated transfer underscores the intrinsic ability of PA to move between membranes, but highlights the need for proteins to ensure rapid and regulated transfer in vivo.
Key Genes Involved in GO:1990050 phosphatidic acid transfer activity
The following genes and proteins are key players in phosphatidic acid transfer activity, as supported by published literature.
| Gene | Major Role | Research Relevance |
|---|---|---|
| RMDN3/PTPIP51 | Regulates PA-binding activity at ER–mitochondria contact sites; involved in mitochondrial function and apoptosis | Target for studying ER–mitochondria communication and neurodegenerative diseases |
| Nir2 | PA-sensing and transfer at ER–PM contact sites; crystal structures reveal PA-binding mechanism | Model for structural studies of lipid transfer proteins |
| Osh6 | Mediates PA transfer in exchange for phosphatidylserine; requires Ist2 for scramblase activity | Yeast model for lipid counter-transport and membrane contact site biology |
| Ist2 | Promotes lipid transfer by Osh6 via membrane tethering and lipid scramblase activities | Component of lipid transfer complexes; potential target for antifungal drugs |
| TMEM16F | Scramblase involved in PA transfer and PIEZO1 coupling; implicated in sickle cell disease | Therapeutic target for sickle cell disease complications |
| PIEZO1 | Mechanosensitive channel coupled to TMEM16F; influences PA transfer and red blood cell function | Target for sickle cell disease and mechanotransduction research |
| NPC2 | Cholesterol transfer protein regulated by acid sphingomyelinase and membrane lipids | Model for lipid transfer in lysosomal storage disorders |
| Acid sphingomyelinase | Regulates cholesterol transfer by NPC2; influences membrane lipid composition | Target for Niemann-Pick disease and lipid metabolism studies |
| Barańska et al. (1988) factor | Non-protein-mediated PA transfer between microsomal and mitochondrial membranes | Historical basis for understanding passive lipid transfer |
| Apoptotic cells | Expose PA for phagocytic recognition; linked to apoptosis and clearance | Model for studying lipid scrambling in cell death |
| Exercise-induced blood factors | Transfer beneficial effects of exercise on neurogenesis and cognition | Link between systemic factors and brain lipid metabolism |
| MITOL | Regulates PA-binding activity of RMDN3/PTPIP51 | Modulator of lipid transfer at ER–mitochondria contacts |
| Phosphatidic acid | Central lipid substrate for transfer activity | Key metabolite in lipid signaling and membrane biogenesis |
| Phosphatidylserine | Counter-transported lipid in Osh6-mediated transfer | Studied in context of lipid asymmetry |
| Cholesterol | Transferred by NPC2; interconnected with PA transfer | Relevant to atherosclerosis and lysosomal disorders |
| PIEZO1-TMEM16F complex | Coupling mitigates sickle cell disease complications | Drug target for sickle cell disease |
How Is phosphatidic acid transfer activity Regulated?
Phosphatidic acid transfer activity is regulated at multiple levels. Post-translational modifications, such as phosphorylation by MITOL, can modulate the PA-binding activity of RMDN3/PTPIP51. Membrane contact site architecture and tethering proteins, such as Ist2, enhance the efficiency of PA transfer by Osh6. The lipid composition of donor and acceptor membranes also influences transfer activity; for example, acid sphingomyelinase activity is regulated by membrane lipids and facilitates cholesterol transfer by NPC2. Additionally, calcium signaling and mechanical forces can regulate scramblase activity of TMEM16F, which is coupled to PIEZO1 in sickle cell disease. These regulatory mechanisms ensure that PA transfer is responsive to cellular demands and integrated with other lipid metabolic pathways.
phosphatidic acid transfer activity and Human Disease
| Gene | Disease / Biology | Potential Experimental Model |
|---|---|---|
| PIEZO1/TMEM16F | Sickle cell disease complications | Patient erythrocytes, sickle cell mouse models, CRISPR knockout of PIEZO1 |
| RMDN3/PTPIP51 | ER–mitochondria communication, apoptosis, neurodegeneration | SH-SY5Y cells, primary neurons, RMDN3 knockout mice |
| Nir2 | ER–PM contact site dysfunction, lipid signaling | HeLa cells, Nir2 knockout, live-cell imaging |
| Osh6/Ist2 | Lipid asymmetry, membrane contact site disorders | Saccharomyces cerevisiae mutants, in vitro lipid transfer assays |
| NPC2/Acid sphingomyelinase | Niemann-Pick disease type C, cholesterol trafficking | NPC2-deficient fibroblasts, mouse models, lipidomics |
Sickle Cell Disease
In sickle cell disease, the coupling between the mechanosensitive channel PIEZO1 and the scramblase TMEM16F contributes to red blood cell dehydration and sickling. Targeting this coupling to mitigate complications has been proposed, and PA transfer activity is implicated in the process. Experimental models include patient-derived erythrocytes and mouse models of sickle cell disease, where pharmacological inhibition of PIEZO1–TMEM16F interaction reduces sickling.
Apoptosis and Clearance of Apoptotic Cells
During apoptosis, phosphatidic acid is exposed on the outer leaflet of the plasma membrane, serving as a signal for phagocytic clearance. This exposure is linked to lipid scrambling and PA transfer activity. Defects in this process can lead to autoimmune diseases due to impaired clearance of apoptotic cells. Research models include Jurkat cells treated with apoptotic stimuli and macrophage phagocytosis assays.
Neurodegeneration and Cognitive Decline
Blood factors released during exercise can transfer beneficial effects on neurogenesis and cognition to the aged brain, potentially involving lipid transfer mechanisms. PA transfer activity may contribute to membrane remodeling in neurons, and its dysregulation could be associated with neurodegenerative conditions. Experimental models include aged mice receiving exercise-conditioned plasma and neurogenesis assays.
Cholesterol Trafficking Disorders
Acid sphingomyelinase regulates cholesterol transfer by NPC2, and this process is influenced by membrane lipids, including PA. Defects in cholesterol trafficking lead to Niemann-Pick type C disease. PA transfer activity may modulate the lipid environment required for NPC2 function. Models include NPC2-deficient fibroblasts and mouse models of Niemann-Pick disease.
From phosphatidic acid transfer activity-Related Genes to Experimental Models
| Research Question | Suitable Model |
|---|---|
| Does knockout of RMDN3/PTPIP51 affect PA transfer at ER–mitochondria contacts? | CRISPR knockout in HeLa or SH-SY5Y cells, followed by PA transfer assays and mitochondrial function tests |
| Can point mutations in Nir2 abolish PA sensing? | CRISPR point mutation knock-in of Nir2 variants, structural and functional analysis |
| What is the effect of TMEM16F overexpression on PA scrambling? | Overexpression of TMEM16F in erythroid cells, flow cytometry for PA exposure |
| Can knock-in of a tagged Osh6 reveal its interaction with Ist2? | CRISPR knock-in of GFP-tagged Osh6 in yeast, co-immunoprecipitation and live imaging |
| Does knockout of NPC2 alter cholesterol transfer? | CRISPR knockout of NPC2 in fibroblasts, cholesterol trafficking assays |
| Can overexpression of PIEZO1 rescue PA transfer defects? | Overexpression of PIEZO1 in sickle cell erythrocytes, measure sickling and PA exposure |
How to Study the phosphatidic acid transfer activity Process
| Method | What It Measures | Typical Application |
|---|---|---|
| Radiolabeled PA transfer assay | Rate and specificity of PA transfer between membranes | In vitro characterization of purified proteins or membrane fractions |
| Fluorescent PA analogs and imaging | Real-time PA distribution and transfer at contact sites | Live-cell imaging of ER–PM or ER–mitochondria contacts |
| CRISPR knockout screens | Identification of genes required for PA transfer | Unbiased discovery of regulators in cell lines |
| Lipidomics | Changes in lipid composition upon perturbation | Quantifying PA and other lipids in knockout or overexpression models |
| Co-immunoprecipitation | Protein–protein interactions in PA transfer complexes | Studying Osh6–Ist2 or PIEZO1–TMEM16F interactions |
| Structural crystallography | Three-dimensional structure of PA-bound proteins | Understanding PA sensing and transfer mechanism |
| Flow cytometry | PA exposure on cell surface | Apoptosis and sickle cell disease studies |
| Neurogenesis assays | Effects of blood factors on neural stem cells | Exercise-induced cognitive improvement models |
Biochemical Transfer Assays
In vitro transfer assays using radiolabeled or fluorescently labeled PA are classic methods to measure PA transfer activity between donor and acceptor membranes. These assays can be performed with purified proteins or membrane fractions, as demonstrated for non-protein-mediated transfer between microsomal and mitochondrial membranes. They allow quantification of transfer rates and specificity.
Fluorescence-Based Lipid Imaging
Live-cell imaging with fluorescent PA analogs or genetically encoded PA sensors enables real-time visualization of PA transfer at membrane contact sites. For example, Nir2 dynamics at ER–PM contact sites have been studied using GFP-tagged proteins and PA biosensors. This method reveals spatial and temporal aspects of PA transfer.
CRISPR Screening and Genetic Perturbation
CRISPR knockout or activation screens can identify genes that regulate PA transfer activity. For instance, targeting candidate genes like RMDN3, Nir2, or Osh6 in cell lines followed by lipidomics or transfer assays can uncover novel regulators. These screens are powerful for unbiased discovery.
Structural Biology and Modeling
Crystal structures of PA transfer proteins, such as Nir2, provide atomic-level insights into substrate binding and conformational changes during transfer. Molecular dynamics simulations complement these studies by modeling the transfer process in silico. Such approaches are essential for understanding the mechanism and for drug design.
How CRISPR Can Be Used to Study GO:1990050 phosphatidic acid transfer activity
Knockout
CRISPR knockout of genes encoding PA transfer proteins, such as RMDN3/PTPIP51, Nir2, or Osh6, allows researchers to assess loss-of-function phenotypes. For example, RMDN3 knockout cells exhibit altered ER–mitochondria contact sites and impaired PA transfer, leading to mitochondrial dysfunction. Knockout models are essential for establishing causality and for identifying compensatory pathways.
Point Mutation
CRISPR point mutation knock-in can introduce specific amino acid substitutions in PA transfer proteins to dissect their functional domains. For instance, mutating the PA-binding pocket of Nir2 can abolish its transfer activity, as guided by crystal structures. Such models are valuable for separating PA transfer from other functions of the protein.
Knock-in
Knock-in of tagged versions of PA transfer proteins (e.g., GFP, HA) enables visualization and purification. Tagged Osh6 knock-in in yeast has been used to study its interaction with Ist2 and its localization to membrane contact sites. Knock-in of disease-associated mutations, such as in TMEM16F, can model sickle cell disease.
Overexpression
Overexpression of PA transfer proteins or their regulators can amplify transfer activity and reveal gain-of-function phenotypes. For example, overexpression of PIEZO1 or TMEM16F in erythroid cells increases PA scrambling and affects sickling. Overexpression models are useful for biochemical purification and for testing therapeutic interventions.
How EDITGENE Supports phosphatidic acid transfer activity Research
Researchers studying phosphatidic acid transfer activity-related genes often need to determine whether a candidate gene is causally involved in lipid transport, membrane contact site function, or disease. EDITGENE provides comprehensive CRISPR-based services to generate precisely engineered cell models, enabling functional validation and mechanistic studies.
Contact EDITGENE today to design your custom CRISPR model for phosphatidic acid transfer activity research.
Frequently Asked Questions About phosphatidic acid transfer activity
What is phosphatidic acid transfer activity?
Phosphatidic acid transfer activity (GO:1990050) is a molecular function that removes phosphatidic acid from a membrane, transports it through the aqueous phase protected in a hydrophobic pocket, and delivers it to an acceptor membrane or lipid particle.
What genes are involved in phosphatidic acid transfer activity?
Key genes include RMDN3/PTPIP51, Nir2, Osh6, Ist2, TMEM16F, PIEZO1, and NPC2, which mediate or regulate PA transfer at membrane contact sites.
How is phosphatidic acid transfer activity regulated?
It is regulated by post-translational modifications (e.g., MITOL-mediated phosphorylation of RMDN3), membrane contact site tethering (e.g., Ist2), and lipid composition (e.g., acid sphingomyelinase).
What diseases are associated with phosphatidic acid transfer activity?
Dysregulation is linked to sickle cell disease, apoptosis-related autoimmune conditions, neurodegeneration, and cholesterol trafficking disorders such as Niemann-Pick disease.
What methods are used to study phosphatidic acid transfer activity?
Common methods include radiolabeled PA transfer assays, fluorescence imaging with PA sensors, CRISPR screens, lipidomics, and structural biology.
Can CRISPR be used to study phosphatidic acid transfer activity?
Yes, CRISPR knockout, point mutation, knock-in, and overexpression models enable functional dissection of PA transfer genes and their roles in disease.
What is the role of TMEM16F in phosphatidic acid transfer?
TMEM16F is a scramblase that, when coupled with PIEZO1, facilitates PA transfer and is implicated in sickle cell disease complications.
How does Nir2 contribute to phosphatidic acid transfer?
Nir2 senses and transfers PA at ER–plasma membrane contact sites, with crystal structures revealing its PA-binding mechanism.
What is the significance of non-protein-mediated PA transfer?
Non-protein-mediated transfer between microsomal and mitochondrial membranes demonstrates that PA can move without proteins, but protein-mediated transfer is faster and regulated.
Which model systems are best for studying phosphatidic acid transfer activity?
Yeast (Osh6/Ist2), mammalian cell lines (HeLa, HEK293T), and mouse models (sickle cell, neurodegeneration) are commonly used, depending on the research question.
Conclusion
Phosphatidic acid transfer activity (GO:1990050) is a fundamental molecular function that ensures proper lipid distribution between cellular membranes. Mediated by proteins such as RMDN3/PTPIP51, Nir2, Osh6, and TMEM16F, this activity is critical for membrane contact site communication, apoptosis, neurogenesis, and cholesterol trafficking. Dysregulation contributes to diseases including sickle cell disease and Niemann-Pick disease, making it a promising therapeutic target. Advances in CRISPR-based models and imaging techniques continue to unravel the mechanistic details and regulatory networks of PA transfer. EDITGENE provides tailored CRISPR services to support researchers in dissecting this important pathway and translating findings into clinical applications.
References
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