GO:0008508 bile acid:sodium symporter activity: Mechanism, Genes and Research Methods
Research-grade guide for scientists and biopharma professionals
Key Takeaways
• GO:0008508 describes a molecular function in which a bile acid and a sodium ion are moved across a membrane together in the same direction, as defined by the reaction bile acid(out) + Na+(out) = bile acid(in) + Na+(in).
• The function is carried out by members of the SLC10 family of solute carriers, including the apical sodium-dependent bile acid transporter (ASBT/SLC10A2) and the sodium-taurocholate cotransporting polypeptide (NTCP/SLC10A1).
• Sodium coupling is not passive: transmembrane domain II of SLC10A2 coordinates sodium translocation, and structural studies of NTCP reveal how nanobody binding locks the transporter in an inhibited state.
• The same activity is conserved beyond mammals, appearing in plant bile acid:sodium symporter family proteins that support glucosinolate biosynthesis and salt tolerance.
• In the liver fluke Clonorchis sinensis, a sodium-bile acid co-transporter is crucial for survival in bile, making it a candidate antiparasitic target.
• Loss of related SLC10A7 function causes a congenital disorder of glycosylation, showing that this transporter family extends beyond classic bile acid transport.
Description
GO:0008508, bile acid:sodium symporter activity, is a molecular function in which a bile acid molecule and a sodium ion are translocated across a membrane together in the same direction. This secondary active transport mechanism is central to the enterohepatic circulation of bile acids and to the uptake of bile acids by cells that express sodium-dependent transporters. The activity is defined by the reaction bile acid(out) + Na+(out) = bile acid(in) + Na+(in), meaning that the inward movement of sodium provides the driving force for bile acid uptake. Because bile acids are detergents that also act as signaling molecules, their controlled transport is essential for normal physiology and is implicated in diarrheal disease, cholestasis and metabolic regulation. Researchers study this activity to understand how SLC10 family transporters achieve substrate recognition and sodium coupling, and to identify targets for drugs and antiparasitic agents. The function is not restricted to mammals: plant bile acid:sodium symporter family proteins participate in methionine-derived glucosinolate biosynthesis and in salt tolerance, indicating deep evolutionary conservation of the transport mechanism.
bile acid:sodium symporter activity At A Glance
| GO ID | GO:0008508 |
|---|---|
| GO term | bile acid:sodium symporter activity |
| Ontology | molecular_function |
| Synonym | sodium/bile acid symporter activity |
| Definition | Enables the transfer of a solute or solutes from one side of a membrane to the other according to the reaction: bile acid(out) + Na+(out) = bile acid(in) + Na+(in). |
| Major function | Sodium-coupled uptake of bile acids across a membrane |
| Representative carriers | SLC10A1 (NTCP), SLC10A2 (ASBT), SLC10A7, plant BASS proteins |
| Directionality | Symport; bile acid and Na+ move in the same direction |
| Research relevance | Bile acid homeostasis, enterohepatic circulation, drug targeting, antiparasitic and plant stress studies |
What Is GO:0008508?
In simple terms, GO:0008508 is the activity of a membrane protein that grabs a bile acid and a sodium ion and carries both of them into the cell at the same time. The QuickGO definition states that this function enables the transfer of a solute or solutes from one side of a membrane to the other according to the reaction bile acid(out) + Na+(out) = bile acid(in) + Na+(in). The synonym sodium/bile acid symporter activity reflects the coupled, same-direction movement of the two substrates. This is a molecular_function term, so it describes what a single transporter protein does rather than a whole pathway or cellular location.
Why Is bile acid:sodium symporter activity Important in Cell Biology?
Bile acid:sodium symporter activity is important because it controls the first step of bile acid reclamation and uptake, and because the transporters that carry it are drug targets and disease genes. In the intestine, apical sodium-dependent bile acid transport determines how much bile acid is recovered, which in turn influences diarrhea and lipid absorption. In the liver, sodium-dependent bile acid uptake is a key determinant of cholestatic injury and of drug-induced transporter inhibition. The same activity is essential for the survival of the liver fluke Clonorchis sinensis in bile, making it a potential antiparasitic target. In plants, bile acid:sodium symporter family proteins contribute to glucosinolate biosynthesis and salt tolerance, linking this molecular function to crop resilience. Finally, mutations in related SLC10A7 cause a congenital disorder of glycosylation, showing that this transporter family has functions beyond bile acid transport.
• Defines the molecular basis of sodium-dependent bile acid uptake in liver and intestine.
• Underlies the enterohepatic circulation that recycles bile acids and regulates lipid digestion.
• Is a pharmacological target because inhibiting ASBT or NTCP alters bile acid flux.
• Contributes to diarrheal disease mechanisms when bile acid reabsorption is impaired.
• Is essential for survival of the liver fluke Clonorchis sinensis in bile.
• Is conserved in plants, where BASS proteins support glucosinolate biosynthesis.
• Is linked to salt tolerance in tomato through SlBASS4.
• Extends to SLC10A7, whose dysfunction causes a glycosylation disorder.
• Provides a structural model for understanding sodium-coupled solute transport.
• Enables CRISPR-based dissection of transporter function in disease models.
Molecular Mechanism of bile acid:sodium symporter activity
Substrate recognition and binding
In simple terms: The transporter first recognizes and binds a bile acid molecule at a specific site.
Bile acid:sodium symporters of the SLC10 family bind bile acids such as taurocholate with high specificity, and structural and mechanistic studies of the apical sodium-dependent bile acid transporter have defined the substrate-binding pocket and the residues that contact the steroid core and the conjugated taurine group. Transmembrane domain II of SLC10A2 is part of this recognition interface and also coordinates sodium translocation, coupling substrate binding to ion movement. The human NTCP structure in a nanobody-inhibited state further reveals how the binding site is occluded when the transporter is locked in an inward-facing or inhibited conformation.
Sodium coupling and conformational cycling
In simple terms: Sodium binding powers a shape change that carries the bile acid across the membrane.
The reaction bile acid(out) + Na+(out) = bile acid(in) + Na+(in) describes a symport mechanism in which sodium and bile acid are translocated together. Mechanistic studies of ASBT indicate that sodium binding to transmembrane domain II triggers conformational rearrangements that open the substrate pathway to the cytoplasm, and that sodium translocation is coordinated by specific residues in this helix. The nanobody-inhibited NTCP structure captures a state in which this conformational cycle is blocked, providing a structural explanation for transport inhibition.
Membrane topology and cellular context
In simple terms: The transporter sits in the cell membrane with its substrate route spanning the lipid bilayer.
Bile acid:sodium symporter activity is a membrane-embedded function, and the proteins that carry it are polytopic membrane proteins with multiple transmembrane helices. In hepatocytes, NTCP mediates sodium-dependent bile acid uptake at the basolateral membrane, while in enterocytes ASBT acts at the apical brush-border membrane, so the same molecular function is deployed at different membrane domains depending on cell type. The activity is therefore best understood as a localized membrane function rather than a soluble enzymatic reaction.
Regulation and inhibition
In simple terms: The activity can be turned up or down by cellular signals and by inhibitor molecules.
Sodium-dependent bile acid transport is regulated at the level of transporter abundance and activity, and it can be blocked by inhibitors; the nanobody-inhibited NTCP structure shows that binding of an inhibitory protein locks the transporter in a non-productive state. Mechanistic work on ASBT has identified residues that are required for sodium-dependent transport, providing a basis for understanding how mutations or drugs alter activity. Because the driving force is the sodium gradient, conditions that dissipate the gradient also reduce bile acid uptake.
Conservation across species
In simple terms: The same transport trick is used by plants and parasites, not just humans.
Bile acid:sodium symporter family proteins are found in plants, where Arabidopsis BASS5 is involved in methionine-derived glucosinolate biosynthesis, and tomato SlBASS4 enhances salt tolerance. In the parasitic liver fluke Clonorchis sinensis, a sodium-bile acid co-transporter is crucial for survival in bile, demonstrating that the activity supports distinct physiological roles in different organisms. This conservation makes the term useful for comparative and evolutionary studies of solute transport.
Key Genes Involved in GO:0008508 bile acid:sodium symporter activity
The genes below encode transporters and related proteins that carry or modulate bile acid:sodium symporter activity across species.
| Gene | Major Role | Research Relevance |
|---|---|---|
| SLC10A2 (ASBT) | Apical sodium-dependent bile acid transporter in intestine | Mechanistic studies of sodium coupling and bile acid reabsorption |
| SLC10A1 (NTCP) | Sodium-dependent bile acid uptake in hepatocytes | Structural and inhibitor studies of bile acid transport |
| SLC10A7 | Transporter family member linked to glycosylation and calcium homeostasis | Disease modeling of SLC10A7-CDG |
| SlBASS4 | Tomato bile acid sodium symporter family protein | Salt tolerance research in crops |
| BASS5 | Arabidopsis bile acid:sodium symporter family protein | Glucosinolate biosynthesis studies |
| CsBAST | Clonorchis sinensis sodium-bile acid co-transporter | Antiparasitic target discovery |
| SLC10A3 | SLC10 family member | Comparative transporter family analysis |
| SLC10A4 | SLC10 family member | Comparative transporter family analysis |
| SLC10A5 | SLC10 family member | Comparative transporter family analysis |
| SLC10A6 | SLC10 family member | Comparative transporter family analysis |
| TMEM2 | Related membrane protein in SLC10A7 studies | Glycosylation pathway research |
| ATP1A1 | Sodium/potassium ATPase that maintains the sodium gradient | Indirect support of sodium-coupled transport |
| SLC10A1 variants | NTCP polymorphisms | Pharmacogenetics of bile acid transport |
| SLC10A2 variants | ASBT polymorphisms | Diarrhea and bile acid malabsorption research |
| BASS family members | Plant bile acid:sodium symporter proteins | Plant stress and secondary metabolism |
| NTCP nanobody target | Inhibitory protein binding site | Structural biology of transport inhibition |
| ASBT transmembrane domain II | Sodium translocation element | Mutagenesis of sodium coupling |
How Is bile acid:sodium symporter activity Regulated?
Bile acid:sodium symporter activity is regulated by the availability of the sodium gradient, by transporter abundance at the membrane, and by inhibitor binding. The nanobody-inhibited NTCP structure demonstrates that protein-protein interactions can lock the transporter in an inhibited state, providing a structural mechanism for regulation. Mechanistic studies of ASBT show that specific residues in transmembrane domain II are required for sodium-dependent transport, so changes in these residues alter activity. In plants, BASS family proteins are integrated into biosynthetic and stress-response pathways, indicating that their activity is tuned to developmental and environmental cues.
bile acid:sodium symporter activity and Human Disease
| Gene | Disease / Biology | Potential Experimental Model |
|---|---|---|
| SLC10A2 | Bile acid malabsorption and diarrhea | Intestinal epithelial KO and point-mutation models |
| SLC10A1 | Cholestasis and drug-induced transporter inhibition | Hepatocyte knock-in and inhibitor-binding models |
| SLC10A7 | SLC10A7-CDG glycosylation disorder | Patient variant knock-in and KO cell models |
| CsBAST | Clonorchis sinensis survival in bile | Parasite transporter inhibition assays |
| SlBASS4 | Salt tolerance in tomato | Plant overexpression and KO lines |
Bile acid malabsorption and diarrhea
Impaired sodium-dependent bile acid reabsorption in the intestine leads to bile acid malabsorption, which is a recognized mechanism of chronic diarrhea. Because ASBT carries bile acid:sodium symporter activity at the apical membrane, changes in its function directly affect the amount of bile acid reaching the colon and the resulting secretory diarrhea.
Cholestasis and liver transporter dysfunction
In the liver, NTCP mediates sodium-dependent bile acid uptake, and its inhibition or dysfunction alters bile acid handling in cholestatic conditions. Structural studies of NTCP in an inhibited state provide a framework for understanding how drugs or inhibitory proteins reduce bile acid uptake and thereby influence liver injury.
SLC10A7-CDG and glycosylation disorders
SLC10A7 regulates O-GalNAc glycosylation and calcium homeostasis in the secretory pathway, and its dysfunction causes SLC10A7-CDG. This links the broader SLC10 transporter family, which includes bile acid:sodium symporters, to congenital disorders of glycosylation and secretory pathway biology.
Parasitic infection and antiparasitic targeting
The liver fluke Clonorchis sinensis depends on a sodium-bile acid co-transporter for survival in bile, so blocking this activity is a potential antiparasitic strategy. This illustrates how a conserved transport function can be exploited as a therapeutic vulnerability in infectious disease.
From bile acid:sodium symporter activity-Related Genes to Experimental Models
| Research Question | Suitable Model |
|---|---|
| Does loss of SLC10A2 abolish intestinal bile acid uptake? | SLC10A2 knockout intestinal cell line |
| Which residues coordinate sodium translocation? | Point-mutation knock-in of transmembrane domain II residues |
| How does inhibitor binding change NTCP conformation? | Tagged knock-in NTCP with structural and binding assays |
| Can SLC10A7 variants reproduce glycosylation defects? | Patient-variant knock-in cells |
| Does SlBASS4 overexpression improve salt tolerance? | Plant overexpression lines |
| Is CsBAST required for parasite survival? | Parasite gene knockout or knockdown |
How to Study the bile acid:sodium symporter activity Process
| Method | What It Measures | Typical Application |
|---|---|---|
| Radiolabeled bile acid uptake | Sodium-dependent transport rate | Confirming GO:0008508 activity |
| Fluorescent bile acid imaging | Cellular bile acid accumulation | Live-cell transporter assays |
| Cryo-EM / crystallography | Transporter conformation | Structural mechanism of inhibition |
| Site-directed mutagenesis | Residue requirement for sodium coupling | Mapping transmembrane domain II function |
| CRISPR knockout screening | Genes required for transport phenotype | Functional genomics of bile acid handling |
| RNA-seq | Transporter gene expression changes | Regulation of SLC10 family genes |
| Plant stress assays | Salt tolerance phenotype | BASS protein function in crops |
| Parasite survival assays | Viability in bile | Antiparasitic target validation |
Transport assays with radiolabeled or fluorescent bile acids
Direct measurement of bile acid:sodium symporter activity uses radiolabeled or fluorescent bile acid substrates in the presence and absence of sodium, allowing calculation of sodium-dependent uptake. These assays are the standard way to confirm that a candidate transporter carries GO:0008508 activity and to test inhibitors.
Structural biology and mutagenesis
Structures of NTCP in a nanobody-inhibited state and mechanistic mutagenesis of ASBT transmembrane domain II reveal the conformational states and residues that underlie sodium-coupled transport. Combining cryo-EM or crystallography with site-directed mutagenesis provides residue-level evidence for the transport mechanism.
CRISPR screens and functional genomics
CRISPR knockout screens can identify genes required for bile acid uptake or for resistance to bile acid stress, and follow-up validation uses targeted knockout or knock-in of SLC10 family genes. Such screens connect GO:0008508 to cellular phenotypes such as glycosylation defects or bile survival.
Comparative and plant physiology approaches
Plant BASS proteins are studied with genetic mutants, expression profiling and stress assays to link bile acid:sodium symporter activity to glucosinolate biosynthesis and salt tolerance. These approaches show how the same molecular function can be analyzed in diverse organisms.
How CRISPR Can Be Used to Study GO:0008508 bile acid:sodium symporter activity
Knockout
CRISPR knockout of SLC10A2 or SLC10A1 removes bile acid:sodium symporter activity and allows researchers to measure the contribution of each transporter to bile acid uptake and downstream phenotypes. Knockout of SLC10A7 in cell models has been used to study glycosylation and calcium homeostasis defects. In parasites, knockout or knockdown of the sodium-bile acid co-transporter can test whether the activity is required for survival in bile.
Point Mutation
Point mutations in transmembrane domain II of SLC10A2 have been used to dissect which residues coordinate sodium translocation, providing residue-level tests of the symport mechanism. Patient-derived point mutations in SLC10A7 can be introduced by CRISPR to model SLC10A7-CDG and to separate transport from glycosylation functions. Such point-mutation models are essential when a complete knockout would be lethal or would obscure subtle mechanistic effects.
Knock-in
Knock-in of tagged or variant transporters allows imaging, binding and structural studies; for example, tagged NTCP knock-in supports analysis of the nanobody-inhibited state. Knock-in of disease-associated SLC10A7 variants provides isogenic models for comparing mutant and wild-type function. Knock-in approaches also enable the study of plant BASS variants in their native genomic context.
Overexpression
Overexpression of SlBASS4 in tomato enhances salt tolerance, demonstrating that increasing bile acid:sodium symporter activity can produce a measurable physiological benefit. Overexpression of SLC10 family transporters in cultured cells is widely used to amplify transport signals for biochemical assays. In parasites, overexpression can be used to test whether increased transporter levels alter bile resistance.
How EDITGENE Supports bile acid:sodium symporter activity Research
Researchers studying bile acid:sodium symporter activity-related genes often need to determine whether a candidate gene is causally involved in bile acid uptake, inhibitor response or disease phenotypes. EDITGENE provides CRISPR-based cell models and screening services that let you move from correlation to causation with validated, publication-ready reagents.
Contact EDITGENE today to design your custom CRISPR model for bile acid:sodium symporter activity research.
Frequently Asked Questions About bile acid:sodium symporter activity
What is bile acid:sodium symporter activity?
It is the molecular function defined by GO:0008508, in which a bile acid and a sodium ion are transported across a membrane together in the same direction according to the reaction bile acid(out) + Na+(out) = bile acid(in) + Na+(in).
What genes are involved in bile acid:sodium symporter activity?
The main genes include SLC10A2 (ASBT), SLC10A1 (NTCP), SLC10A7, plant BASS proteins such as BASS5 and SlBASS4, and the Clonorchis sinensis sodium-bile acid co-transporter.
Which GO ID corresponds to bile acid:sodium symporter activity?
The GO ID is GO:0008508, a molecular_function term with the synonym sodium/bile acid symporter activity.
How does sodium drive bile acid transport?
Sodium binding to the transporter, including residues in transmembrane domain II of SLC10A2, triggers conformational changes that carry the bile acid into the cell along with sodium.
What is the role of SLC10A2 in the intestine?
SLC10A2 encodes the apical sodium-dependent bile acid transporter, which mediates intestinal bile acid reabsorption and is linked to bile acid malabsorption and diarrhea.
What is the role of NTCP in the liver?
NTCP (SLC10A1) mediates sodium-dependent bile acid uptake in hepatocytes, and its inhibited structure has been solved with a nanobody.
Is bile acid:sodium symporter activity found in plants?
Yes, plant bile acid:sodium symporter family proteins such as Arabidopsis BASS5 and tomato SlBASS4 are involved in glucosinolate biosynthesis and salt tolerance.
How is bile acid:sodium symporter activity studied experimentally?
Common methods include radiolabeled or fluorescent bile acid uptake assays, structural biology, site-directed mutagenesis, CRISPR knockout or knock-in models, and plant stress assays.
What diseases are linked to this activity?
It is linked to bile acid malabsorption and diarrhea, cholestasis, SLC10A7-CDG glycosylation disorder, and parasitic survival of Clonorchis sinensis in bile.
Can CRISPR be used to study bile acid:sodium symporter activity?
Yes, CRISPR knockout, point mutation, knock-in and overexpression models allow causal testing of SLC10 family transporters and related genes in disease and transport assays.
Conclusion
GO:0008508, bile acid:sodium symporter activity, is a well-defined molecular function that couples bile acid movement to the sodium gradient and is carried out by conserved SLC10 family transporters in animals, plants and parasites. Its mechanistic details, including sodium coordination by transmembrane domain II and inhibitor-induced conformational locking, are increasingly well understood through structural and mutagenesis studies. Because the activity is linked to diarrhea, cholestasis, glycosylation disorders and antiparasitic vulnerability, it remains an active area for CRISPR-based functional studies and therapeutic development.
References
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- 4. Sawada Y et al.. 2009. Arabidopsis bile acid:sodium symporter family protein 5 is involved in methionine-derived glucosinolate biosynthesis.. Plant Cell Physiol 50(9):1579-86 PMID: 19633020
- 5. Durin Z et al.. 2025. SLC10A7 regulates O-GalNAc glycosylation and Ca(2+) homeostasis in the secretory pathway: insights into SLC10A7-CDG.. Cell Mol Life Sci 82(1):40 PMID: 39779512
- 6. Alhadeff R et al.. 2015. Mechanistic studies of the apical sodium-dependent bile acid transporter.. Proteins 83(6):1107-17 PMID: 25820648
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