GO:0140327 flippase activity: Mechanism, Genes and Research Methods
Research-grade guide for scientists and biopharma professionals
Key Takeaways
• GO:0140327 flippase activity is a molecular_function describing ATP-dependent catalysis of lipid movement from the exoplasmic to the cytosolic leaflet of a membrane.
• Flippases are P4-ATPases that maintain asymmetric phospholipid distribution, keeping phosphatidylserine (PS) and phosphatidylethanolamine (PE) enriched in the inner leaflet.
• Loss of flippase activity causes surface exposure of PS, a signal for apoptosis clearance, platelet procoagulant activity, and erythrocyte senescence.
• The lipid flippase SLC47A1 (also known as MATE1) blocks metabolic vulnerability to ferroptosis, linking flippase activity to cell death regulation.
• Flippase inhibition enhances caspofungin efficacy in drug-resistant fungi, demonstrating therapeutic potential of targeting flippase activity.
• TAT-5 flippase activity is required for sperm activation and restricts extracellular vesicle budding from the plasma membrane.
Description
Flippase activity (GO:0140327) is a molecular_function defined as the catalysis of lipid movement from the exoplasmic to the cytosolic leaflet of a membrane, using energy from ATP hydrolysis. This activity is essential for establishing and maintaining the asymmetric distribution of phospholipids across biological membranes, a fundamental feature of eukaryotic cells. The plasma membrane of eukaryotic cells is not a symmetric bilayer; phosphatidylserine (PS) and phosphatidylethanolamine (PE) are predominantly located in the inner (cytosolic) leaflet, while phosphatidylcholine and sphingomyelin are enriched in the outer (exoplasmic) leaflet. Flippases, together with scramblases, regulate this phospholipid asymmetry. Researchers study flippase activity because it controls key cellular processes including apoptosis, blood coagulation, ferroptosis, and extracellular vesicle biogenesis. For example, the exposure of PS on the outer leaflet of apoptotic cells is a signal for phagocytic clearance, and this exposure results from loss of flippase activity combined with scramblase activation. In platelets, maintaining flippase activity reduces thrombin generation, suggesting that flippase function is critical for hemostasis. In erythrocytes, reduced flippase activity contributes to PS surface presentation during senescence. Flippase activity is also implicated in fungal drug resistance and fertilization. Butyrolactol A enhances caspofungin efficacy via flippase inhibition in drug-resistant fungi. In sperm, robust TAT-5 lipid flippase activity is required for activation for fertilization. The ATPase activity of the PE flippase TAT-5 inhibits extracellular vesicle budding from the plasma membrane. These diverse roles make flippase activity a compelling target for both basic research and therapeutic development.
flippase activity At A Glance
| GO ID | GO:0140327 |
|---|---|
| GO term | flippase activity |
| Ontology | molecular_function |
| Synonym | flippase activity (exoplasmic to cytosolic leaflet) |
| Major function | ATP-dependent translocation of lipids from the exoplasmic to the cytosolic leaflet of a membrane |
| Energy source | ATP hydrolysis |
| Substrates | Phosphatidylserine, phosphatidylethanolamine, and other phospholipids |
| Cellular context | Plasma membrane and other organelle membranes |
| Related activity | Scramblase activity (ATP-independent, bidirectional) |
What Is GO:0140327?
Flippase activity (GO:0140327) is the ATP-dependent catalysis of lipid transport from the exoplasmic (outer) leaflet to the cytosolic (inner) leaflet of a membrane. This activity is mediated by P4-ATPases, which couple ATP hydrolysis to the translocation of specific phospholipids, primarily phosphatidylserine and phosphatidylethanolamine, against their concentration gradient. The term is synonymous with flippase activity (exoplasmic to cytosolic leaflet) and is distinct from scramblase activity, which moves lipids bidirectionally down their concentration gradient in an ATP-independent manner.
Why Is flippase activity Important in Cell Biology?
Flippase activity is fundamentally important because it establishes and maintains the asymmetric distribution of phospholipids across cellular membranes, which is critical for membrane integrity, cell signaling, and the recognition of apoptotic cells. Disruption of flippase activity leads to aberrant exposure of phosphatidylserine on the cell surface, which can trigger blood coagulation, promote phagocytosis of living cells, or contribute to disease pathology. Moreover, flippase activity is emerging as a therapeutic target in fungal infections and cancer, as inhibition of flippases can enhance antifungal drug efficacy or modulate ferroptosis sensitivity.
• Maintains phospholipid asymmetry, essential for membrane barrier function and cell viability.
• Regulates apoptotic cell clearance by controlling phosphatidylserine exposure.
• Modulates blood coagulation by limiting procoagulant platelet activity.
• Protects against ferroptosis through SLC47A1-mediated lipid remodeling.
• Contributes to erythrocyte senescence and removal from circulation.
• Required for sperm activation and fertilization.
• Restricts extracellular vesicle budding from the plasma membrane.
• Represents a target for antifungal therapy in drug-resistant fungi.
• Involved in lipid homeostasis and membrane trafficking.
What Happens During flippase activity?
Substrate Recognition and Binding
In simple terms: The flippase enzyme first grabs a specific lipid molecule on the outer side of the membrane.
Flippases, primarily P4-ATPases, recognize and bind specific phospholipids such as phosphatidylserine and phosphatidylethanolamine in the exoplasmic leaflet. This binding is thought to involve a conserved substrate-binding pocket within the transmembrane domain of the flippase. The specificity of flippases for different lipid headgroups contributes to the distinct lipid compositions of the two membrane leaflets.
ATP Hydrolysis and Conformational Change
In simple terms: The enzyme uses energy from ATP to change its shape, which pushes the lipid across the membrane.
Upon substrate binding, the flippase hydrolyzes ATP, which drives a conformational change in the protein. This change is coupled to the translocation of the lipid substrate across the membrane bilayer. The ATPase activity of the flippase is essential for its function; for example, the ATPase activity of the phosphatidylethanolamine flippase TAT-5 inhibits extracellular vesicle budding from the plasma membrane.
Lipid Translocation and Release
In simple terms: The lipid is flipped to the inner side of the membrane and released.
Following the conformational change, the lipid is moved from the exoplasmic to the cytosolic leaflet and released into the inner leaflet. This translocation is unidirectional and against the concentration gradient, requiring continuous ATP hydrolysis. The released lipid then contributes to the inner leaflet's lipid pool, maintaining the asymmetric distribution characteristic of healthy cells.
Regulation by Scramblases and Other Factors
In simple terms: Other proteins can counteract the flippase by scrambling lipids in both directions.
Flippase activity is counterbalanced by scramblases, which move lipids bidirectionally down their concentration gradient in an ATP-independent manner. The balance between flippase and scramblase activities determines the steady-state distribution of phospholipids. In apoptotic cells, caspase activation leads to inactivation of flippases and activation of scramblases, resulting in phosphatidylserine exposure.
Key Genes Involved in GO:0140327 flippase activity
The following genes encode proteins that exhibit flippase activity or are directly involved in its regulation and function.
| Gene | Major Role | Research Relevance |
|---|---|---|
| ATP8A1 | P4-ATPase flippase that translocates phosphatidylserine and phosphatidylethanolamine | Studied for its role in membrane asymmetry and vesicle trafficking |
| ATP8A2 | P4-ATPase flippase highly expressed in the brain and retina | Mutations linked to neurological disorders; used to study lipid asymmetry in neurons |
| ATP8B1 | P4-ATPase flippase involved in bile canalicular membrane asymmetry | Associated with progressive familial intrahepatic cholestasis; model for liver disease |
| ATP8B2 | P4-ATPase flippase with broad tissue distribution | Investigated for its role in lipid homeostasis and membrane dynamics |
| ATP9A | P4-ATPase flippase involved in endosomal recycling | Studied for its role in vesicle transport and membrane remodeling |
| ATP9B | P4-ATPase flippase localized to the Golgi apparatus | Investigated for its function in secretory pathway lipid asymmetry |
| ATP10A | P4-ATPase flippase associated with metabolic traits | Linked to obesity and insulin resistance in genome-wide association studies |
| ATP10B | P4-ATPase flippase expressed in the brain | Associated with Parkinson's disease risk; studied in neurodegeneration |
| ATP10D | P4-ATPase flippase involved in sphingolipid metabolism | Investigated for its role in lipid metabolism and cardiovascular disease |
| ATP11A | P4-ATPase flippase that translocates phosphatidylserine | Studied for its role in apoptosis and platelet function |
| ATP11B | P4-ATPase flippase involved in endosomal trafficking | Investigated for its role in membrane dynamics and cancer |
| ATP11C | P4-ATPase flippase critical for B cell development | Mutations cause immunodeficiency; model for lymphocyte biology |
| TAT-5 | P4-ATPase flippase in C. elegans that translocates phosphatidylethanolamine | Studied for its role in extracellular vesicle budding and sperm activation |
| SLC47A1 | Multidrug and toxin extrusion protein 1 with flippase activity | Blocks metabolic vulnerability to ferroptosis; studied in cancer and kidney disease |
| CDC50A | Chaperone subunit required for P4-ATPase flippase function | Essential for proper folding and trafficking of flippases; knockout models used |
| CDC50B | Chaperone subunit for P4-ATPases | Investigated for its role in flippase complex assembly |
| TMEM30A | Chaperone subunit for P4-ATPases | Studied for its role in lipid asymmetry and viral entry |
| TMEM30B | Chaperone subunit for P4-ATPases | Investigated for its role in flippase function in epithelial cells |
How Is flippase activity Regulated?
Flippase activity is regulated at multiple levels, including protein expression, subcellular localization, and post-translational modifications. The activity of P4-ATPases is dependent on association with CDC50 family chaperone subunits, which are required for their exit from the endoplasmic reticulum and proper folding. In apoptotic cells, caspase-mediated cleavage of flippases leads to loss of activity, contributing to phosphatidylserine exposure. In platelets, maintaining flippase activity is a novel approach to reducing thrombin generation, suggesting that flippase function can be modulated pharmacologically. Additionally, the lipid flippase SLC47A1 is regulated in response to metabolic stress and influences ferroptosis sensitivity. In C. elegans, TAT-5 flippase activity is regulated during sperm activation for fertilization.
flippase activity and Human Disease
| Gene | Disease / Biology | Potential Experimental Model |
|---|---|---|
| ATP11A | Apoptosis and platelet procoagulant activity | Knockout in HeLa cells; platelet-specific KO mice |
| SLC47A1 | Ferroptosis resistance in cancer | Overexpression and knockout in cancer cell lines; xenograft models |
| ATP8B1 | Progressive familial intrahepatic cholestasis | Liver-specific knockout mice; patient-derived hepatocytes |
| ATP10B | Parkinson's disease risk | Neuronal knockout models; iPSC-derived neurons |
| TAT-5 | Fertilization defects and extracellular vesicle budding | C. elegans mutants; sperm activation assays |
Flippase Activity in Apoptosis and Autoimmunity
Loss of flippase activity is a hallmark of apoptosis, leading to phosphatidylserine exposure on the cell surface, which serves as an 'eat-me' signal for phagocytes. Defective clearance of apoptotic cells can contribute to autoimmune diseases such as systemic lupus erythematosus, where impaired flippase function may lead to secondary necrosis and release of autoantigens.
Flippase Activity and Thrombosis
In platelets, maintaining flippase activity is critical for limiting procoagulant activity. Reduced flippase activity leads to phosphatidylserine exposure on platelets, promoting thrombin generation and increasing thrombotic risk. Pharmacological strategies to maintain flippase activity in platelets represent a novel approach to reducing thrombin generation and potentially preventing thrombosis.
Flippase Activity in Ferroptosis and Cancer
The lipid flippase SLC47A1 blocks metabolic vulnerability to ferroptosis, a form of iron-dependent cell death. Loss of SLC47A1-mediated flippase activity sensitizes cancer cells to ferroptosis, suggesting that targeting flippase activity could be a therapeutic strategy in cancers resistant to conventional therapies.
Flippase Activity in Fungal Infections
Butyrolactol A enhances caspofungin efficacy via flippase inhibition in drug-resistant fungi, demonstrating that flippase activity is a viable antifungal target. Inhibiting fungal flippases disrupts membrane asymmetry and cell wall integrity, sensitizing resistant strains to echinocandin drugs.
From flippase activity-Related Genes to Experimental Models
| Research Question | Suitable Model |
|---|---|
| Does loss of flippase activity cause phosphatidylserine exposure? | Knockout of ATP11A or ATP11C in cell lines followed by annexin V staining |
| Can a point mutation in the ATPase domain abolish flippase activity? | CRISPR-mediated point mutation of the catalytic glutamate in ATP8A1 |
| Does restoring flippase activity rescue a disease phenotype? | Knock-in of wild-type ATP8B1 in patient-derived cells |
| Where is the flippase localized in live cells? | Tagged knock-in of ATP11A with GFP for live-cell imaging |
| Does overexpression of SLC47A1 protect against ferroptosis? | Overexpression of SLC47A1 in cancer cell lines treated with ferroptosis inducers |
| What is the effect of flippase inhibition on fungal drug resistance? | Knockout of fungal flippase genes in Candida albicans and caspofungin sensitivity assays |
How to Study the flippase activity Process
| Method | What It Measures | Typical Application |
|---|---|---|
| Annexin V staining | Phosphatidylserine exposure on the cell surface | Apoptosis, platelet activation, erythrocyte senescence |
| Fluorescent lipid analogs | Flippase-mediated lipid translocation | Real-time monitoring of lipid movement in live cells |
| ATPase activity assay | Rate of ATP hydrolysis by flippases | Enzymatic characterization of flippase mutants |
| CRISPR library screening | Genes regulating flippase activity or synthetic lethality | Discovery of novel regulators and drug targets |
| Live-cell imaging | Subcellular localization and dynamics of flippases | Trafficking and membrane remodeling studies |
| Flow cytometry | Quantification of PS-positive cells | High-throughput screening of flippase modulators |
| Liposome reconstitution | Lipid translocation by purified flippase complexes | Biochemical dissection of flippase mechanism |
| Mass spectrometry | Lipid composition of membrane leaflets | Lipidomic profiling of flippase mutants |
Annexin V Staining and Flow Cytometry
Annexin V staining is widely used to detect phosphatidylserine exposure on the outer leaflet of the plasma membrane, a direct consequence of reduced flippase activity. Flow cytometry allows quantification of PS-positive cells and is commonly applied to study apoptosis, platelet activation, and erythrocyte senescence.
Fluorescent Lipid Analogs and Live-Cell Imaging
Fluorescently labeled lipid analogs, such as NBD-labeled phosphatidylserine, can be used to monitor flippase-mediated lipid translocation in real time. Live-cell imaging of cells expressing fluorescently tagged flippases enables visualization of their subcellular localization and dynamics.
ATPase Activity Assays
ATPase activity assays measure the rate of ATP hydrolysis by flippases, providing a direct readout of their catalytic activity. These assays are often performed with purified flippase complexes reconstituted into liposomes or with membrane fractions from cells.
Genetic Screens and CRISPR Libraries
CRISPR library screening can identify genes that regulate flippase activity or that are synthetically lethal with flippase loss. Such screens have revealed components of the lipid asymmetry machinery and potential therapeutic targets.
How CRISPR Can Be Used to Study GO:0140327 flippase activity
Knockout
CRISPR knockout of flippase genes such as ATP11A, ATP11C, or TAT-5 allows researchers to study the consequences of loss of flippase activity on lipid asymmetry, apoptosis, and development. Knockout cell lines and animal models have been instrumental in linking flippase activity to phosphatidylserine exposure and disease phenotypes.
Point Mutation
CRISPR-mediated point mutations can be introduced into the catalytic domain of flippases to abolish ATPase activity without affecting protein expression or localization. Such models are valuable for distinguishing the enzymatic activity of flippases from their structural roles.
Knock-in
Knock-in of wild-type or mutant flippase genes, often tagged with fluorescent proteins or epitope tags, enables precise tracking of flippase localization and function in vivo. Knock-in models can also be used to rescue phenotypes caused by flippase deficiency.
Overexpression
Overexpression of flippases such as SLC47A1 or ATP8A1 can be achieved by CRISPR-mediated insertion of a strong promoter or by lentiviral transduction. Overexpression studies help determine whether increased flippase activity is sufficient to protect against ferroptosis or to alter membrane asymmetry.
How EDITGENE Supports flippase activity Research
Researchers studying flippase activity-related genes often need to determine whether a candidate gene is causally involved in lipid asymmetry, cell death, or disease. EDITGENE provides comprehensive CRISPR-based services to generate precisely engineered cell models for functional studies of flippase activity and its regulatory network.
Contact EDITGENE today to design your custom CRISPR model for flippase activity research.
Frequently Asked Questions About flippase activity
What is flippase activity?
Flippase activity (GO:0140327) is the ATP-dependent catalysis of lipid movement from the exoplasmic to the cytosolic leaflet of a membrane, maintaining phospholipid asymmetry.
What genes are involved in flippase activity?
Key genes include P4-ATPases such as ATP8A1, ATP8A2, ATP8B1, ATP11A, ATP11C, and TAT-5, as well as the non-ATPase SLC47A1 and chaperone subunits like CDC50A.
How is flippase activity measured?
Flippase activity is measured using annexin V staining for phosphatidylserine exposure, fluorescent lipid analogs for translocation, and ATPase activity assays for enzymatic function.
What is the difference between flippase and scramblase?
Flippases move lipids unidirectionally from the exoplasmic to the cytosolic leaflet using ATP, while scramblases move lipids bidirectionally down their concentration gradient without ATP.
Why is flippase activity important for apoptosis?
Loss of flippase activity during apoptosis leads to phosphatidylserine exposure on the cell surface, which signals for phagocytic clearance of dying cells.
Can flippase activity be targeted for antifungal therapy?
Yes, butyrolactol A enhances caspofungin efficacy by inhibiting flippase activity in drug-resistant fungi, suggesting a potential therapeutic strategy.
What diseases are associated with flippase dysfunction?
Flippase dysfunction is linked to autoimmune diseases, thrombosis, progressive familial intrahepatic cholestasis, Parkinson's disease risk, and cancer ferroptosis resistance.
How does SLC47A1 flippase activity affect ferroptosis?
SLC47A1 flippase activity blocks metabolic vulnerability to ferroptosis, and its loss sensitizes cells to ferroptosis inducers.
Is flippase activity required for fertilization?
Yes, robust TAT-5 lipid flippase activity is required for sperm activation for fertilization in C. elegans.
What CRISPR models are available for studying flippase activity?
Knockout, point mutation, knock-in, tagged knock-in, and overexpression models can be generated for flippase genes to study their function and regulation.
Conclusion
Flippase activity (GO:0140327) is a fundamental molecular function that maintains phospholipid asymmetry across cellular membranes, with critical roles in apoptosis, coagulation, ferroptosis, and fertilization. Dysregulation of flippase activity contributes to a range of human diseases, including autoimmune disorders, thrombosis, liver disease, and cancer. Targeting flippase activity also holds promise for antifungal therapy. Continued research using CRISPR-based models will further elucidate the mechanisms and therapeutic potential of flippase activity.
References
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- 2. Millington-Burgess SL et al.. 2022. Maintaining flippase activity in procoagulant platelets is a novel approach to reducing thrombin generation.. J Thromb Haemost 20(4):989-995 PMID: 35034417
- 3. Chen X et al.. 2026. Butyrolactol A enhances caspofungin efficacy via flippase inhibition in drug-resistant fungi.. Cell 189(2):620-639.e28 PMID: 41478284
- 4. Sakuragi T et al.. 2023. Regulation of phospholipid distribution in the lipid bilayer by flippases and scramblases.. Nat Rev Mol Cell Biol 24(8):576-596 PMID: 37106071
- 5. Pitts LR et al.. 2023. The ATPase activity of the phosphatidylethanolamine flippase TAT-5 inhibits extracellular vesicle budding from the plasma membrane.. MicroPubl Biol 2023 PMID: 37038482
- 6. Maniates KA et al.. 2025. Sperm activation for fertilization requires robust activity of the TAT-5 lipid flippase.. Dev Biol 528:66-78 PMID: 40915529
- 7. Seki M et al.. 2020. Reduction in flippase activity contributes to surface presentation of phosphatidylserine in human senescent erythrocytes.. J Cell Mol Med 24(23):13991-14000 PMID: 33103382
- 8. Lin Z et al.. 2022. The lipid flippase SLC47A1 blocks metabolic vulnerability to ferroptosis.. Nat Commun 13(1):7965 PMID: 36575162
