Placental Lactogen Caprine
Description
Molecular Composition
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Primary Structure: cPL consists of a single polypeptide chain with 199 amino acids, including an additional N-terminal alanine residue .
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Disulfide Bonds: Contains two intrachain disulfide bonds critical for structural stability .
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Homology: Shares 85% sequence homology with ovine placental lactogen (oPL) .
Maternal Adaptations
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Metabolic Regulation:
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Lactogenic Activity: Binds prolactin receptors (PRLRs) to promote mammary gland development and β-casein synthesis .
Fetal Development
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Growth Promotion: Weak agonist of growth hormone receptors (GHRs), supporting fetal tissue proliferation .
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Nutrient Partitioning: Directs maternal glucose and lipids toward fetal growth .
Receptor Binding and Signaling
Expression Dynamics During Pregnancy
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Maternal Circulation:
Clinical Correlations
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Maternal Obesity: Lower cPL levels correlate with reduced placental mass and impaired fetal growth .
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Gestational Diabetes: Elevated cPL concentrations linked to macrosomia and insulin resistance .
Biological Activity Assays
| Assay Model | Result | Source |
|---|---|---|
| Nb2 Cell Proliferation | ED₅₀ = 1.5 nM | |
| β-Casein Synthesis | 80% stimulation in ovine mammary acini | |
| FDC-P1 Cell Proliferation | EC₅₀ = 0.8 nM (rabbit GHR) |
Biomarker Potential
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Pregnancy Monitoring: Serum cPL levels reflect placental health and fetal growth trajectory .
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Metabolic Disorders: Dysregulated cPL secretion correlates with gestational diabetes and intrauterine growth restriction .
Recombinant cPL Applications
Product Specs
Q&A
Methodologies for Purifying Recombinant Caprine Placental Lactogen (cPL)
Caprine PL can be purified from E. coli inclusion bodies using a two-step chromatography approach. After refolding, proteins are subjected to Q-Sepharose anion-exchange chromatography followed by SP-Sepharose cation-exchange chromatography, yielding two fractions: cPL-Q (from Q-Sepharose) and cPL-S (from SP-Sepharose). Both fractions exhibit >98% monomeric purity and a molecular mass of ~23 kDa . This method ensures removal of host-cell proteins and aggregates, critical for downstream receptor-binding and bioactivity assays.
Receptor-Binding Specificity of Caprine PL vs. Other Species
Caprine PL binds to prolactin receptors (PRLR) and growth hormone receptors (GHR) with distinct stoichiometry. It forms 1:2 complexes with rabbit/human GHRs and rat/rabbit PRLRs but 1:1 complexes with bovine PRLR . This contrasts with ovine PL, which binds bovine PRLR similarly to cPL . Bovine PL, in turn, exhibits weaker GH-like activity compared to caprine PL .
| Receptor Type | Species | Complex Stoichiometry | Source |
|---|---|---|---|
| GHR | Rabbit | 1:2 | |
| GHR | Human | 1:2 | |
| PRLR | Rabbit | 1:2 | |
| PRLR | Bovine | 1:1 | |
| GHR | Bovine | Low affinity |
Interpreting Divergence in Lactogenic vs. GH-Like Activity Near Parturition
During late pregnancy, lactogenic activity (prolactin-like) persists at ~700 ng/ml near parturition, while GH-like activity declines to <200 ng/ml . This divergence likely reflects pituitary prolactin secretion surging prepartum, which cross-reacts in lactogenic assays but not GH-like assays. Researchers must differentiate between placental-derived cPL and pituitary prolactin using chromatographic separation (e.g., Sephadex G-100) .
Challenges in Radioreceptor Assay (RRA) Data Interpretation
RRA data for cPL require careful validation to avoid cross-reactivity:
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Species-Specific Receptors: Bovine PRLR may not detect cPL as effectively as rabbit/human PRLR .
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Pituitary Hormone Contamination: Maternal serum near parturition may contain endogenous prolactin, necessitating acidification steps or immunoprecipitation to isolate cPL .
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Receptor Conformation: Use of solubilized vs. membrane-bound receptors affects binding affinity measurements .
Experimental Design for Studying cPL’s Role in Fetal Growth
To investigate cPL’s impact on fetal development:
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Model Selection: Use ovine models for lentiviral shRNA-mediated PL knockdown, as shown in studies reducing PL mRNA by ~50% and fetal weight by ~32% .
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Endpoints: Measure IGF-1/IGF-2 mRNA in fetal liver and placental weight to assess growth restriction .
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Controls: Include vehicle-treated and non-target shRNA groups to rule out off-target effects .
Comparative Analysis of cPL vs. Human PL Receptor Specificity
While human PL primarily binds prolactin receptors, cPL exhibits dual affinity for PRLR and GHR . This divergence impacts metabolic regulation:
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Glucose Metabolism: Human PL promotes insulin resistance via PRLR-mediated signaling, whereas cPL may also activate GHR pathways .
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Lipolysis: Unlike human PL, cPL does not induce lipolysis in adipose tissue, suggesting species-specific metabolic roles .
Optimizing Refolding Conditions for Recombinant cPL
Key parameters for refolding cPL from inclusion bodies:
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pH Gradient: Use Q-Sepharose at pH 8.0–9.0 to elute monomeric cPL, avoiding aggregation .
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Redox Environment: Include 1 mM DTT or glutathione redox buffer to maintain disulfide bonds .
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Protein Concentration: Maintain <1 mg/ml to prevent aggregation during dialysis .
Species-Specific Antibodies for cPL Detection
Antibodies raised against bovine PL may cross-react weakly with cPL due to structural homology (~70% sequence similarity). For precise quantification:
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Radioimmunoassay (RIA): Validate antibodies against cPL using placental cotyledon extracts .
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Western Blotting: Use anti-His tag antibodies if recombinant cPL includes a His-tag .
Contradictions in cPL Serum Levels Between Species
Applications of cPL in Mammary Gland Research
Caprine PL stimulates β-casein synthesis in rabbit/ovine mammary acini cultures, mimicking lactogenic signaling . For mechanistic studies:
Product Science Overview
Placental Lactogen Caprine Recombinant is biologically active and has been shown to induce the proliferation of Nb2 cells, indicating its functional similarity to natural placental lactogen . It is also capable of activating human and other heterologous growth hormone receptors but not ruminant growth hormone receptors .
The lyophilized form of Placental Lactogen Caprine Recombinant is stable at room temperature for up to three weeks. However, for long-term storage, it should be kept desiccated below -18°C. Upon reconstitution, it should be stored at 4°C for short-term use (2-7 days) and below -18°C for long-term use. To prevent degradation, it is recommended to add a carrier protein such as 0.1% HSA or BSA and avoid freeze-thaw cycles .
