GO:0001850 complement component C3a binding: Mechanism, Genes and Research Methods
Research-grade guide for scientists and biopharma professionals
Key Takeaways
• GO:0001850 (complement component C3a binding) is a molecular_function term describing the selective, non-covalent interaction of a protein or receptor with C3a, the 77-residue anaphylatoxin released from complement component C3 during complement activation [1,7].
• C3a is generated when C3 convertases cleave C3 into C3a and C3b; C3a retains the C-terminal arginine (C3a-desArg is the carboxypeptidase-cleaved form), and both forms can engage C3a-binding proteins [1,3,7].
• The best-characterized C3a-binding protein is the G-protein-coupled receptor C3AR1 (C3aR), whose activation triggers calcium flux, MAPK signaling and chemotaxis in myeloid and structural cells [3,8].
• C3a binding is central to host defense, inflammation, neuromyelitis optica lesion evolution, and liver failure outcome, making it a tractable target for CRISPR-based functional interrogation [2,4,6].
• C3a-binding interactions can be studied with radioligand binding, surface plasmon resonance, BRET/GRK recruitment assays, and PET tracers such as those targeting C3aR [3,8].
• EDITGENE supports C3a-binding research with C3, C3AR1 and C5AR1 knockout, point-mutation, knock-in, overexpression cell models plus CRISPR library screening and bioinformatics.
Description
GO:0001850, complement component C3a binding, is a Gene Ontology molecular_function term defined as binding to a C3a product of the complement cascade. C3a is a small anaphylatoxin generated when the complement component C3 is proteolytically cleaved by C3 convertases during activation of the complement system [1,7]. The term therefore captures the selective, non-covalent association of a protein with C3a, and it is distinct from binding to intact C3, to C3b, or to the desArginated metabolite C3a-desArg, although C3a-desArg can also engage some receptors [1,3]. Researchers care about GO:0001850 because C3a binding is the first step in a signaling axis that links innate immune recognition to inflammation, chemotaxis, and tissue injury. The canonical C3a-binding protein is the seven-transmembrane receptor C3AR1, which couples to Gi/o proteins and drives calcium mobilization, ERK phosphorylation, and directed cell migration. C3a binding also participates in antibacterial immunity in teleost models, where C3 and activated C3a are required for complement activation and host defense. In human disease, C3a binding and signaling contribute to astrocyte-microglia crosstalk in neuromyelitis optica lesions, to poor outcome in hepatitis B virus-related acute-on-chronic liver failure when plasma C3/C3a levels are low, and to complement-driven kidney pathology in C3 glomerulopathy. Because C3a binding sits at the interface of ligand recognition and receptor activation, it is an attractive node for CRISPR-based dissection. Knockout of C3 or C3AR1 abolishes ligand or receptor, respectively, while point mutations in the C3a-binding pocket of C3AR1 can separate binding from activation. This article summarizes the QuickGO definition, the molecular mechanism, the key genes, disease links, and the experimental models and methods used to study GO:0001850.
complement component C3a binding At A Glance
| GO ID | GO:0001850 |
|---|---|
| GO term | complement component C3a binding |
| Ontology | molecular_function |
| Synonym | none listed in QuickGO |
| Definition | Binding to a C3a product of the complement cascade. |
| Major function | Selective non-covalent recognition of the C3a anaphylatoxin by receptors and soluble proteins |
| Canonical ligand | C3a, a 77-amino-acid fragment released from complement C3 |
| Canonical receptor | C3AR1 (C3a receptor 1), a Gi/o-coupled GPCR |
| Related ligand form | C3a-desArg, generated by carboxypeptidase removal of the C-terminal arginine |
| Downstream readouts | Calcium flux, MAPK/ERK activation, chemotaxis, cytokine release [3,6] |
What Is GO:0001850?
In plain terms, GO:0001850 describes the ability of a protein to physically bind C3a, the small fragment released from complement component C3 during complement activation. The QuickGO definition is binding to a C3a product of the complement cascade. This is a molecular_function annotation: it describes what a gene product does at the molecular level, not where it acts or which pathway it belongs to. C3a binding is mediated by defined structural elements, such as the extracellular loops of the C3a receptor C3AR1, and it can be measured biochemically by ligand-binding assays [3,7].
Why Is complement component C3a binding Important in Cell Biology?
GO:0001850 matters because C3a binding is the molecular trigger for anaphylatoxin signaling, a process that shapes innate immunity, inflammation, and tissue repair. The interaction between C3a and C3AR1 is one of the best-characterized complement receptor-ligand pairs, and structural and pharmacological work has revealed how binding energy is converted into receptor activation and biased signaling. Because C3a is generated whenever complement is activated, C3a-binding proteins are positioned to sense infection, sterile injury, and immune-complex deposition. This makes the term directly relevant to antibacterial defense, to central nervous system inflammation such as neuromyelitis optica, to liver failure prognosis, and to complement-mediated kidney disease. For drug discovery, C3a-binding interfaces are targetable, as shown by PET radiotracers that engage C3aR and by fusion proteins that reduce kidney complement in experimental C3 glomerulopathy [5,8].
• C3a binding initiates anaphylatoxin signaling through C3AR1, a Gi/o-coupled GPCR that mobilizes calcium and activates MAPK.
• C3a is a 77-residue fragment of C3 whose primary structure was determined in early protein chemistry work, providing the molecular basis for binding studies.
• C3a binding contributes to antibacterial immunity, as shown in teleost models where C3 and activated C3a are required for complement activation and host defense.
• Astrocyte-microglia interaction in evolving neuromyelitis optica lesions involves complement and C3a-dependent crosstalk.
• Low plasma C3 and C3a levels are associated with poor outcome in hepatitis B virus-related acute-on-chronic liver failure, linking C3a biology to clinical prognosis.
• C3a-binding and complement effector functions are being targeted in C3 glomerulopathy, where a novel fusion protein reduces kidney complement in experimental models.
• PET radiotracers targeting the C3a receptor enable non-invasive imaging of C3a-binding sites in vivo.
• C3-dependent effector functions of complement, including C3a generation and recognition, are central to host defense and pathology.
• C3a binding is a druggable node: receptor antagonists and ligand-directed biologics can interrupt the axis [3,5].
• CRISPR knockout of C3 or C3AR1 provides clean genetic tests of whether a phenotype requires C3a binding [1,3].
Molecular Mechanism of complement component C3a binding
Generation of the C3a ligand
In simple terms: C3a is cut out of a larger protein when complement is activated.
C3a is released when C3 convertases cleave complement component C3 into C3a and C3b during complement activation. The C3a fragment is a 77-amino-acid polypeptide whose primary structure was determined by Hugli, establishing the molecular identity of the ligand recognized in GO:0001850. Because C3a carries a C-terminal arginine, it can be converted to C3a-desArg by carboxypeptidases, and both forms can participate in C3-dependent effector functions. The availability of C3a therefore depends on upstream complement activation and on the balance between convertase activity and carboxypeptidase trimming [1,6].
Recognition by C3a-binding proteins
In simple terms: Receptors and soluble proteins grab C3a through shape-complementary pockets.
The canonical C3a-binding protein is C3AR1, a class A GPCR that recognizes C3a through its extracellular loops and transmembrane pocket. Molecular basis studies of anaphylatoxin binding, activation, and signaling bias at complement receptors have defined how C3a docks into C3AR1 and how the binding energy is transduced to the intracellular G-protein interface. Binding is selective: C3a engages C3AR1, whereas the related anaphylatoxin C5a engages C5AR1, and receptor chimeras and mutagenesis have mapped determinants of this specificity. Soluble C3a-binding proteins also exist and contribute to C3-dependent effector functions.
Receptor activation and signaling bias
In simple terms: Once C3a is bound, the receptor switches on and can favor different downstream routes.
C3a binding stabilizes an active conformation of C3AR1 that couples to Gi/o proteins, leading to inhibition of adenylyl cyclase, calcium mobilization, and MAPK/ERK activation. The same study showed that complement receptors can display signaling bias, meaning that different ligands or receptor conformations preferentially activate distinct downstream pathways. This bias is relevant to drug discovery because it implies that C3a-binding modulators could selectively tune inflammation versus chemotaxis. Downstream, C3a-driven signals promote chemotaxis and cytokine production in myeloid cells and can act on structural cells such as astrocytes [2,3].
C3a binding in host defense and inflammation
In simple terms: C3a binding helps the body fight bacteria but can also drive tissue damage.
In antibacterial immunity, C3 and activated C3a are involved in complement activation and host defense, as demonstrated in a teleost model where these components are required for effective bacterial killing. In the central nervous system, astrocyte-microglia interaction drives evolving neuromyelitis optica lesions, and complement-dependent C3a signaling contributes to this crosstalk. In clinical settings, lower plasma levels of C3 and C3a are associated with poor outcome in patients with hepatitis B virus-related acute-on-chronic liver failure, indicating that C3a generation and recognition are relevant to disease severity. Together, these findings show that GO:0001850 is not a passive binding event but a decision point between protection and pathology [1,2,6].
Pharmacological and imaging interrogation of C3a binding
In simple terms: Drugs and tracers can be used to see or block C3a binding.
C3a-binding sites can be interrogated pharmacologically with receptor antagonists and with radiolabeled ligands, and PET radiotracers targeting the complement C3a receptor have been developed for in vivo imaging. In experimental C3 glomerulopathy, a novel fusion protein reduces kidney complement, demonstrating that therapeutic interception of the C3/C3a axis is feasible. These tools complement genetic approaches and allow researchers to test whether a phenotype depends on C3a binding specifically or on other C3-dependent effector functions [1,5,8].
Key Genes Involved in GO:0001850 complement component C3a binding
The genes and proteins most directly relevant to GO:0001850 include the ligand C3, its receptor C3AR1, and the broader complement and anaphylatoxin network that determines C3a availability and signaling.
| Gene | Major Role | Research Relevance |
|---|---|---|
| C3 | Precursor of C3a and C3b; cleaved by C3 convertases during complement activation | Knockout abolishes C3a generation and is the cleanest genetic test of C3a-dependent phenotypes [1,6] |
| C3AR1 | Canonical G-protein-coupled receptor that binds C3a and transduces anaphylatoxin signals | Knockout or point mutation separates C3a binding from receptor activation and signaling bias |
| C5AR1 | Receptor for the related anaphylatoxin C5a; structural comparator for C3a binding specificity | Useful for specificity controls and for studying anaphylatoxin receptor evolution |
| C5 | Precursor of C5a; component of the terminal complement pathway | Helps distinguish C3a-dependent from C5a-dependent effector functions |
| CFB | Factor B, a serine protease that forms the C3 convertase with C3b | Modulating CFB changes C3a generation and can be used to titrate ligand availability |
| CFD | Factor D, which activates factor B in the alternative pathway | Knockout reduces alternative-pathway C3a production |
| CFH | Factor H, a negative regulator of the alternative pathway | Loss of CFH increases complement activation and C3a generation |
| CFI | Factor I, which cleaves C3b in the presence of cofactors | Regulates the balance between C3b and downstream C3a production |
| C4 | Forms the C3 convertase of the classical and lectin pathways | Determines classical-pathway contribution to C3a generation |
| C4BPA | C4b-binding protein, a regulator of the classical pathway | Modulates upstream complement activation and C3a release |
| CD46 | Membrane cofactor protein that regulates complement on host cells | Controls cell-surface complement activation and local C3a production |
| CD55 | Decay-accelerating factor that destabilizes C3 convertases | Loss increases C3a generation on cell surfaces |
| CR1 | Complement receptor 1 with decay-accelerating and cofactor activity | Regulates C3 convertase lifetime and C3a output |
| CPB2 | Carboxypeptidase that generates C3a-desArg from C3a | Determines the ratio of C3a to C3a-desArg available for binding |
| GNAI1 | Gi/o alpha subunit that couples to C3AR1 after C3a binding | Knockout or point mutation blocks C3a-driven calcium and MAPK signaling |
| ARRB1 | Beta-arrestin 1, involved in GPCR desensitization and biased signaling | Modulates C3a receptor signaling bias and internalization |
| ARRB2 | Beta-arrestin 2, involved in GPCR desensitization and biased signaling | Modulates C3a receptor signaling bias and internalization |
| MAPK1 | ERK2, a downstream kinase activated by C3a binding | Readout of C3a receptor activation in cells and tissues |
How Is complement component C3a binding Regulated?
C3a binding is regulated at three levels: ligand availability, receptor availability, and signal termination. Ligand availability depends on complement activation, because C3a is produced when C3 convertases cleave C3, and on carboxypeptidase trimming of the C-terminal arginine to generate C3a-desArg [1,7]. Regulators such as factor H, factor I, CD46, CD55, and CR1 control convertase lifetime and therefore the amount of C3a generated on host surfaces. Receptor availability and responsiveness are regulated by C3AR1 expression, by GPCR desensitization and internalization, and by beta-arrestin recruitment, which can also shape signaling bias. In disease settings, the balance between C3a and C3a-desArg, and the presence of competing anaphylatoxins such as C5a, further tune the effective C3a-binding signal [1,3].
complement component C3a binding and Human Disease
| Gene | Disease / Biology | Potential Experimental Model |
|---|---|---|
| C3 | Hepatitis B virus-related acute-on-chronic liver failure; low C3/C3a associates with poor outcome | C3 knockout hepatocyte or macrophage cell lines; plasma C3a ELISA in patient samples |
| C3AR1 | Neuromyelitis optica lesion evolution; C3a-driven microglial activation | C3AR1 knockout microglia or astrocyte-microglia co-culture models [2,3] |
| C3 | C3 glomerulopathy; dysregulated alternative pathway complement | C3 or CFH knockout models with complement-reducing fusion protein treatment |
| C3AR1 | Anaphylatoxin signaling bias and inflammation | C3AR1 point-mutation knock-in cells with BRET and calcium-flux readouts |
| C3 | Antibacterial immunity in teleost models | C3 knockout fish or macrophage lines challenged with bacteria |
Neuromyelitis optica and CNS inflammation
Astrocyte-microglia interaction drives evolving neuromyelitis optica lesions, and complement-dependent signals including C3a contribute to this crosstalk. C3a binding to C3AR1 on microglia and other myeloid cells can amplify chemotaxis and cytokine release, which in turn shapes lesion evolution [2,3]. This makes GO:0001850 relevant to demyelinating disease biology and to the development of complement-directed therapies for CNS inflammation.
Liver failure and infection
Lower levels of complement component C3 and C3a in plasma are associated with poor outcome in patients with hepatitis B virus-related acute-on-chronic liver failure. Because C3a is generated from C3, reduced C3a availability may reflect impaired complement activation and compromised antibacterial immunity in these patients [4,6]. C3a binding and signaling are therefore candidate biomarkers and mechanistic nodes in acute-on-chronic liver failure.
C3 glomerulopathy and kidney complement
C3 glomerulopathy is driven by dysregulated alternative-pathway complement activation, and a novel fusion protein has been shown to reduce kidney complement in experimental models of the disease. Because C3a is generated during complement activation, C3a-binding events are part of the effector landscape in the kidney, and therapeutic interception of the C3/C3a axis is an active strategy [1,5]. This links GO:0001850 to renal pathology and to complement-targeted drug development.
Antibacterial immunity and host defense
Complement C3 and activated fragment C3a are involved in complement activation and anti-bacterial immunity, as shown in a teleost infection model. C3a binding to its receptor contributes to the inflammatory and chemotactic responses that recruit immune cells to sites of infection [3,6]. This positions GO:0001850 within host-defense biology and within comparative immunology across vertebrates.
From complement component C3a binding-Related Genes to Experimental Models
| Research Question | Suitable Model |
|---|---|
| Does a phenotype require C3a generation? | C3 knockout cell line or animal, with C3a ELISA and complement activation readouts [1,6] |
| Does C3a binding to C3AR1 drive signaling? | C3AR1 knockout cells reconstituted with wild-type or binding-pocket mutant receptor |
| Which residues mediate C3a binding specificity? | C3AR1 point-mutation knock-in or site-directed mutants with radioligand binding [3,7] |
| Can C3a binding be imaged in vivo? | C3AR1-targeted PET radiotracer in disease models |
| Does C3a binding contribute to kidney complement injury? | Experimental C3 glomerulopathy model treated with complement-reducing fusion protein |
| Is C3a binding required for antibacterial defense? | C3 knockout or C3a-binding-deficient model challenged with bacteria |
How to Study the complement component C3a binding Process
| Method | What It Measures | Typical Application |
|---|---|---|
| Radioligand binding assay | Affinity and specificity of C3a binding to receptors [3,7] | Characterizing C3AR1 mutants and antagonist potency |
| Calcium flux assay | Gi/o-mediated intracellular calcium release after C3a binding | Functional screening of C3a receptor agonists and antagonists |
| BRET / beta-arrestin recruitment | G-protein activation and signaling bias | Detecting biased ligands at complement receptors |
| MAPK/ERK phosphorylation | Downstream kinase activation after C3a binding | Confirming receptor-proximal signaling in cells |
| PET imaging with C3aR tracer | In vivo distribution of C3a-binding sites | Non-invasive imaging of inflammation and target engagement |
| C3a ELISA | Ligand concentration in plasma or supernatant | Clinical prognosis and complement activation monitoring |
| CRISPR knockout and knock-in | Causal role of C3 and C3AR1 in phenotypes [1,3] | Target validation in cell and animal models [1,3] |
| Co-culture and chemotaxis assays | Cell migration and crosstalk driven by C3a [2,3] | Modeling neuromyelitis optica and myeloid recruitment |
Ligand-binding assays
Direct measurement of GO:0001850 uses radiolabeled or fluorescently labeled C3a in saturation and competition binding assays on cells expressing C3AR1 or related receptors [3,7]. These assays define affinity, specificity, and the ability of antagonists to compete with C3a. Because C3a and C3a-desArg differ at the C-terminus, binding assays can also distinguish ligand forms [1,7].
Functional signaling assays
C3a binding is coupled to Gi/o-dependent signaling, so calcium mobilization, cAMP inhibition, and MAPK/ERK phosphorylation are standard functional readouts. BRET or bioluminescence assays can monitor G-protein activation and beta-arrestin recruitment, which is particularly useful for detecting signaling bias at complement receptors. These assays link the binding event to downstream cellular responses.
Imaging and in vivo tracer studies
PET radiotracers targeting the complement C3a receptor allow non-invasive visualization of C3a-binding sites in living animals. Such tracers can be used to quantify receptor availability in inflammation or infection models and to support target engagement studies for C3aR-directed drugs. They complement ex vivo autoradiography and immunohistochemistry.
Genetic and CRISPR-based perturbation
CRISPR knockout of C3 or C3AR1, together with point-mutation knock-in of receptor residues, provides causal tests of C3a-binding function [1,3]. These models can be combined with complement activation assays, cytokine profiling, and chemotaxis assays to determine whether a phenotype depends on C3a binding specifically [2,3,6]. Overexpression of tagged C3a or C3AR1 enables affinity purification and interaction proteomics.
How CRISPR Can Be Used to Study GO:0001850 complement component C3a binding
Knockout
CRISPR knockout of C3 eliminates the precursor of C3a, providing a clean way to test whether a phenotype depends on C3a generation and binding [1,6]. Knockout of C3AR1 removes the canonical C3a receptor and blocks C3a-driven calcium flux, MAPK activation, and chemotaxis. These models are essential controls when interpreting complement-directed therapeutics, because they distinguish ligand-dependent from receptor-dependent effects [1,3].
Point Mutation
Point mutations in the C3a-binding pocket of C3AR1 can separate ligand binding from receptor activation, which is critical for understanding signaling bias. Site-directed mutants of C3a itself can also be used to map the epitope recognized by receptors and soluble C3a-binding proteins. These reagents allow precise structure-function dissection of GO:0001850 without confounding changes in protein abundance [3,7].
Knock-in
Knock-in of tagged C3a or C3AR1 enables affinity purification, live-cell imaging, and interaction proteomics under endogenous regulatory control. Knock-in of disease-associated or signaling-biased receptor variants can model how C3a binding translates into pathology in conditions such as neuromyelitis optica or C3 glomerulopathy [2,5]. Tagged knock-in lines also support PET tracer validation and receptor trafficking studies.
Overexpression
Overexpression of C3, C3a, or C3AR1 in cell lines amplifies the C3a-binding signal and facilitates biochemical assays such as radioligand binding and BRET [3,8]. Overexpression systems are useful for screening antagonists and for producing recombinant receptor for structural studies. They should be interpreted alongside knockout data because supraphysiological expression can alter signaling bias and receptor desensitization.
How EDITGENE Supports complement component C3a binding Research
Researchers studying complement component C3a binding-related genes often need to determine whether a candidate gene is causally involved in ligand generation, receptor recognition, or downstream signaling. EDITGENE provides the CRISPR cell models and screening services needed to move from correlation to causation in C3a biology.
Contact EDITGENE today to design your custom CRISPR model for complement component C3a binding research.
Frequently Asked Questions About complement component C3a binding
What is GO:0001850 complement component C3a binding?
GO:0001850 is a Gene Ontology molecular_function term defined as binding to a C3a product of the complement cascade. C3a is a 77-residue anaphylatoxin released from complement component C3 during complement activation [1,7].
What genes are involved in complement component C3a binding?
The key genes are C3, which encodes the C3a precursor, and C3AR1, which encodes the canonical C3a receptor. Complement regulators such as CFH, CFI, CD46, CD55, and CR1 control C3a generation, while GNAI1, ARRB1, and ARRB2 shape downstream signaling [1,3].
Which receptor binds C3a?
C3AR1 (C3a receptor 1) is the canonical G-protein-coupled receptor that binds C3a and transduces anaphylatoxin signals through Gi/o proteins.
How is C3a generated?
C3a is generated when C3 convertases cleave complement component C3 into C3a and C3b during complement activation. The C3a fragment is a 77-amino-acid polypeptide whose primary structure was determined by Hugli.
What is the difference between C3a and C3a-desArg?
C3a carries a C-terminal arginine that can be removed by carboxypeptidases to produce C3a-desArg. Both forms can participate in C3-dependent effector functions, and the ratio can influence receptor engagement [1,7].
What diseases are linked to C3a binding?
C3a binding and signaling have been linked to neuromyelitis optica lesion evolution, hepatitis B virus-related acute-on-chronic liver failure, C3 glomerulopathy, and antibacterial immunity [2,4,5,6].
How can I study C3a binding in the lab?
Common methods include radioligand binding assays, calcium flux, BRET and beta-arrestin recruitment, MAPK phosphorylation, C3a ELISA, and PET imaging with C3aR-targeted tracers [3,4,8].
Can CRISPR be used to study C3a binding?
Yes. CRISPR knockout of C3 or C3AR1, point-mutation knock-in of the C3a-binding pocket, and tagged knock-in of C3a or C3AR1 are all established approaches for causal studies of GO:0001850 [1,3].
What is signaling bias at complement receptors?
Signaling bias means that different ligands or receptor conformations preferentially activate distinct downstream pathways. Molecular studies of anaphylatoxin binding at complement receptors have demonstrated this phenomenon for C3a and related ligands.
Is C3a binding a drug target?
Yes. C3a-binding interfaces can be targeted with receptor antagonists, ligand-directed biologics, and fusion proteins, and PET tracers targeting C3aR have been developed for in vivo imaging [3,5,8].
Conclusion
GO:0001850 complement component C3a binding captures a precise molecular event: the selective recognition of the C3a anaphylatoxin by receptors and soluble proteins. This event links complement activation to calcium flux, MAPK signaling, chemotaxis, and inflammation, and it is implicated in neuromyelitis optica, liver failure, C3 glomerulopathy, and antibacterial immunity [1,2,3,4,5,6]. Because C3a binding can be measured biochemically and perturbed genetically, it is an excellent target for CRISPR-based functional studies [3,7,8]. Researchers can now combine knockout, point-mutation, knock-in, and overexpression models with binding and signaling assays to determine exactly how C3a recognition shapes disease. EDITGENE provides these models and the accompanying screening and bioinformatics support to accelerate discovery in complement biology.
References
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- 3. Yadav MK et al.. 2023. Molecular basis of anaphylatoxin binding, activation, and signaling bias at complement receptors.. Cell 186(22):4956-4973.e21 PMID: 37852260
- 4. Li Q et al.. 2020. Lower level of complement component C3 and C3a in the plasma means poor outcome in the patients with hepatitis B virus related acute-on-chronic liver failure.. BMC Gastroenterol 20(1):106 PMID: 32293297
- 5. Malik TH et al.. 2026. A novel fusion protein reduces kidney complement in experimental C3 glomerulopathy.. Clin Exp Immunol 220(1) PMID: 41810513
- 6. Wu M et al.. 2022. Complement C3 and Activated Fragment C3a Are Involved in Complement Activation and Anti-Bacterial Immunity.. Front Immunol 13:813173 PMID: 35281048
- 7. Hugli TE. 1975. Human anaphylatoxin (C3a) from the third component of complement. Primary structure.. J Biol Chem 250(21):8293-301 PMID: 1238393
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