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Detailed Production Guide for Recombinant Human Growth Hormone (rHGH, Somatropin)
The gene of interest does not include the signal peptide sequence for secretion in this expression system.
1.2 Codon Optimization and Synthesis
Optimize the DNA sequence for high expression in Escherichia coli (E. coli). This involves changing codons to those preferred by E. coli without altering the amino acid sequence. Use an online tool like IDT's Codon Optimization Tool.
Add restriction enzyme sites to the 5' and 3' ends for cloning. For example, add an NdeI site (CATATG) which includes the ATG start codon, and an XhoI site (CTCGAG) after the stop codon (TAA).
Add a C-terminal hexahistidine (6xHis) tag (sequence CAC CAC CAC CAC CAC CAC) before the stop codon. This tag is crucial for purification via immobilized metal affinity chromatography (IMAC).
Submit the final designed sequence to a commercial gene synthesis company (like IDT, Twist, or GenScript) to be cloned into a standard cloning vector (e.g., pUC57).
1.3 Vector Construction
Expression Vector: Use pET-21a(+) or a similar high-expression vector designed for E. coli. This vector has a T7 promoter for strong, inducible expression.
Cloning:
Digest both the synthesized gene fragment (from pUC57) and the pET-21a(+) vector with NdeI and XhoI restriction enzymes.
Purify the digested products using agarose gel electrophoresis and a gel extraction kit.
Ligate the insert into the linearized vector using T4 DNA Ligase. Use a 3:1 molar ratio of insert to vector.
Transform the ligation mixture into chemically competent E. coli DH5α cells for plasmid propagation.
Plate on LB agar containing ampicillin (100 µg/mL) and incubate overnight at 37°C.
Verification:
Pick several colonies and grow them in LB + ampicillin broth.
Isolate the plasmid DNA using a miniprep kit.
Verify the correct insert and sequence by Sanger sequencing.
2. Strain Preparation and Small-Scale Expression Testing
2.1 Expression Strain Selection
Use an E. coli strain optimized for protein expression, such as BL21(DE3), Rosetta(DE3), or Origami(DE3). BL21(DE3) is the standard choice. The (DE3) indicates it has the T7 RNA polymerase gene under the control of the lac promoter, which is necessary for expression from the T7 promoter in the pET vector.
2.2 Transformation
Transform the verified pET-21a(+)-hGH plasmid into chemically competent BL21(DE3) cells.
Plate on LB agar + ampicillin and incubate overnight.
2.3 Small-Scale Expression Test
Inoculate a single colony into 5 mL of LB + ampicillin (100 µg/mL). Grow overnight at 37°C with shaking (200 rpm).
The next day, inoculate 50 mL of fresh LB + ampicillin with 0.5 mL of the overnight culture (1:100 dilution).
Grow at 37°C with shaking until the optical density at 600nm (OD600) reaches 0.6-0.8.
Induction: Add Isopropyl β-D-1-thiogalactopyranoside (IPTG) to a final concentration of 1 mM.
Expression Conditions (Test different options):
Option A (Standard): Continue incubation at 37°C for 4 hours.
Option B (Low Temp): Reduce temperature to 18°C and incubate overnight (12-16 hours). This often promotes solubility.
Harvest: Pellet the cells by centrifugation at 4,000 x g for 15 minutes at 4°C. Discard the supernatant. Store the cell pellet at -20°C.
2.4 Analysis
Resuspend the cell pellet in lysis buffer (e.g., 50mM Tris-HCl, pH 8.0, 100mM NaCl). Lyse the cells by sonication (e.g., 10 seconds on, 20 seconds off, for 5 minutes total on ice).
Centrifuge the lysate at 12,000 x g for 20 minutes at 4°C to separate the soluble fraction (supernatant) from the insoluble fraction (pellet, which contains inclusion bodies).
Analyze both fractions using SDS-PAGE to determine if the HGH is soluble or forming inclusion bodies. For HGH, inclusion bodies are common and require a refolding step.
3. Large-Scale Production
3.1 Fermentation
Inoculate 1 L of LB + ampicillin in a 2.5 L baffled flask with the optimized expression conditions determined in step 2.
Grow at 37°C to OD600 of 0.6-0.8.
Induce with 1 mM IPTG and shift to the optimal temperature (e.g., 18°C) for overnight expression.
Harvest cells by centrifugation (4,000 x g, 20 min, 4°C). The cell paste can be stored at -80°C.
4. Inclusion Body Isolation and Solubilization
4.1 Cell Lysis and Inclusion Body Isolation
Thaw cell paste on ice. Resuspend in ice-cold lysis buffer (50mM Tris-HCl, pH 8.0, 100mM NaCl, 1mM EDTA, 1 mg/mL lysozyme). Add a protease inhibitor cocktail.
Incubate on ice for 30 minutes.
Sonicate the suspension on ice to ensure complete cell disruption.
Centrifuge at 15,000 x g for 30 minutes at 4°C. The pellet contains inclusion bodies and cell debris.
Wash the pellet with wash buffer (50mM Tris-HCl, pH 8.0, 1M urea, 1% Triton X-100) to remove membrane lipids and contaminants. Vortex and centrifuge again. Repeat 2-3 times.
Perform a final wash with buffer without detergent (50mM Tris-HCl, pH 8.0, 1M urea).
4.2 Solubilization
Solubilize the washed inclusion body pellet in solubilization buffer (50mM Tris-HCl, pH 8.0, 6M Guanidine Hydrochloride or 8M Urea, 10mM Dithiothreitol (DTT)). The DTT keeps cysteines reduced.
Stir at room temperature for 1-2 hours until the pellet is completely dissolved.
Centrifuge at 20,000 x g for 30 minutes to remove insoluble debris. The supernatant now contains the denatured, reduced HGH.
5. Refolding and Purification
5.1 Refolding by Dilution
This completes the detailed guide for the research-grade production of recombinant Human Growth Hormone.
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- Gene Synthesis and Vector Construction
1.1 Sequence Acquisition
The gene of interest does not include the signal peptide sequence for secretion in this expression system.
1.2 Codon Optimization and Synthesis
Optimize the DNA sequence for high expression in Escherichia coli (E. coli). This involves changing codons to those preferred by E. coli without altering the amino acid sequence. Use an online tool like IDT's Codon Optimization Tool.
Add restriction enzyme sites to the 5' and 3' ends for cloning. For example, add an NdeI site (CATATG) which includes the ATG start codon, and an XhoI site (CTCGAG) after the stop codon (TAA).
Add a C-terminal hexahistidine (6xHis) tag (sequence CAC CAC CAC CAC CAC CAC) before the stop codon. This tag is crucial for purification via immobilized metal affinity chromatography (IMAC).
Submit the final designed sequence to a commercial gene synthesis company (like IDT, Twist, or GenScript) to be cloned into a standard cloning vector (e.g., pUC57).
1.3 Vector Construction
Expression Vector: Use pET-21a(+) or a similar high-expression vector designed for E. coli. This vector has a T7 promoter for strong, inducible expression.
Cloning:
Digest both the synthesized gene fragment (from pUC57) and the pET-21a(+) vector with NdeI and XhoI restriction enzymes.
Purify the digested products using agarose gel electrophoresis and a gel extraction kit.
Ligate the insert into the linearized vector using T4 DNA Ligase. Use a 3:1 molar ratio of insert to vector.
Transform the ligation mixture into chemically competent E. coli DH5α cells for plasmid propagation.
Plate on LB agar containing ampicillin (100 µg/mL) and incubate overnight at 37°C.
Verification:
Pick several colonies and grow them in LB + ampicillin broth.
Isolate the plasmid DNA using a miniprep kit.
Verify the correct insert and sequence by Sanger sequencing.
2. Strain Preparation and Small-Scale Expression Testing
2.1 Expression Strain Selection
Use an E. coli strain optimized for protein expression, such as BL21(DE3), Rosetta(DE3), or Origami(DE3). BL21(DE3) is the standard choice. The (DE3) indicates it has the T7 RNA polymerase gene under the control of the lac promoter, which is necessary for expression from the T7 promoter in the pET vector.
2.2 Transformation
Transform the verified pET-21a(+)-hGH plasmid into chemically competent BL21(DE3) cells.
Plate on LB agar + ampicillin and incubate overnight.
2.3 Small-Scale Expression Test
Inoculate a single colony into 5 mL of LB + ampicillin (100 µg/mL). Grow overnight at 37°C with shaking (200 rpm).
The next day, inoculate 50 mL of fresh LB + ampicillin with 0.5 mL of the overnight culture (1:100 dilution).
Grow at 37°C with shaking until the optical density at 600nm (OD600) reaches 0.6-0.8.
Induction: Add Isopropyl β-D-1-thiogalactopyranoside (IPTG) to a final concentration of 1 mM.
Expression Conditions (Test different options):
Option A (Standard): Continue incubation at 37°C for 4 hours.
Option B (Low Temp): Reduce temperature to 18°C and incubate overnight (12-16 hours). This often promotes solubility.
Harvest: Pellet the cells by centrifugation at 4,000 x g for 15 minutes at 4°C. Discard the supernatant. Store the cell pellet at -20°C.
2.4 Analysis
Resuspend the cell pellet in lysis buffer (e.g., 50mM Tris-HCl, pH 8.0, 100mM NaCl). Lyse the cells by sonication (e.g., 10 seconds on, 20 seconds off, for 5 minutes total on ice).
Centrifuge the lysate at 12,000 x g for 20 minutes at 4°C to separate the soluble fraction (supernatant) from the insoluble fraction (pellet, which contains inclusion bodies).
Analyze both fractions using SDS-PAGE to determine if the HGH is soluble or forming inclusion bodies. For HGH, inclusion bodies are common and require a refolding step.
3. Large-Scale Production
3.1 Fermentation
Inoculate 1 L of LB + ampicillin in a 2.5 L baffled flask with the optimized expression conditions determined in step 2.
Grow at 37°C to OD600 of 0.6-0.8.
Induce with 1 mM IPTG and shift to the optimal temperature (e.g., 18°C) for overnight expression.
Harvest cells by centrifugation (4,000 x g, 20 min, 4°C). The cell paste can be stored at -80°C.
4. Inclusion Body Isolation and Solubilization
4.1 Cell Lysis and Inclusion Body Isolation
Thaw cell paste on ice. Resuspend in ice-cold lysis buffer (50mM Tris-HCl, pH 8.0, 100mM NaCl, 1mM EDTA, 1 mg/mL lysozyme). Add a protease inhibitor cocktail.
Incubate on ice for 30 minutes.
Sonicate the suspension on ice to ensure complete cell disruption.
Centrifuge at 15,000 x g for 30 minutes at 4°C. The pellet contains inclusion bodies and cell debris.
Wash the pellet with wash buffer (50mM Tris-HCl, pH 8.0, 1M urea, 1% Triton X-100) to remove membrane lipids and contaminants. Vortex and centrifuge again. Repeat 2-3 times.
Perform a final wash with buffer without detergent (50mM Tris-HCl, pH 8.0, 1M urea).
4.2 Solubilization
Solubilize the washed inclusion body pellet in solubilization buffer (50mM Tris-HCl, pH 8.0, 6M Guanidine Hydrochloride or 8M Urea, 10mM Dithiothreitol (DTT)). The DTT keeps cysteines reduced.
Stir at room temperature for 1-2 hours until the pellet is completely dissolved.
Centrifuge at 20,000 x g for 30 minutes to remove insoluble debris. The supernatant now contains the denatured, reduced HGH.
5. Refolding and Purification
5.1 Refolding by Dilution
- Refolding is the most critical step. Prepare a large volume of ice-cold refolding buffer: 50mM Tris-HCl, pH 8.5, 0.5M L-Arginine, 2mM reduced glutathione (GSH), 0.2mM oxidized glutathione (GSSG). The arginine helps prevent aggregation, and the GSH/GSSG pair promotes correct disulfide bond formation (HGH has two).
- Rapidly dilute the solubilized protein solution dropwise into the refolding buffer with vigorous stirring. The final concentration of GuHCl/Urea should be below 0.5M, and the final protein concentration should be low (e.g., 0.1 mg/mL) to minimize aggregation.
- Stir the refolding mixture at 4°C for 12-24 hours.
- Concentrate the refolded solution and exchange the buffer to binding buffer (e.g., 20mM sodium phosphate, pH 7.4, 300mM NaCl) using tangential flow filtration (TFF) or a centrifugal concentrator with a 3 kDa molecular weight cut-off (MWCO) membrane.
- Column: Use a Ni-NTA or Co-NTA agarose column (e.g., 5 mL HisTrap HP column from GE Healthcare).
- Equilibration: Equilibrate the column with 5 column volumes (CV) of binding buffer (20mM sodium phosphate, pH 7.4, 300mM NaCl).
- Loading: Load the concentrated, refolded sample onto the column at a flow rate of 1 mL/min. The 6xHis tag will bind to the nickel ions.
- Washing: Wash the column with 10 CV of binding buffer containing 20mM imidazole to remove weakly bound, non-specific proteins.
- Elution: Elute the bound HGH with a linear gradient of elution buffer (20mM sodium phosphate, pH 7.4, 300mM NaCl, 500mM imidazole) from 20mM to 500mM imidazole over 20 CV. Collect 1 mL fractions.
- Analysis: Analyze fractions by SDS-PAGE. Pool the fractions containing pure HGH (identified by a single band at ~22 kDa).
- The 6xHis tag is not present in native somatropin. To obtain the native sequence, the tag must be removed.
- Protease Cleavage: If a protease cleavage site (e.g., TEV protease site) was engineered between the HGH and the His-tag, dialyze the pooled fractions into cleavage buffer (e.g., 50mM Tris-HCl, pH 8.0, 0.5mM EDTA, 1mM DTT) and add the protease at a 1:50 (w/w) protease:target ratio. Incubate at 4°C overnight.
- Reverse-IMAC: Pass the cleavage mixture over the Ni-NTA column again. The cleaved, native HGH will flow through, while the His-tag, any uncleaved protein, and the His-tagged protease will bind to the column. Collect the flow-through, which contains the purified, native HGH.
- This step removes any remaining host cell proteins, DNA, or aggregates.
- Cation Exchange (e.g., SP Sepharose):
- Buffer A: 20mM sodium acetate, pH 5.0.
- Buffer B: 20mM sodium acetate, pH 5.0, 1M NaCl.
- Procedure: Adjust the HGH solution to pH 5.0. Load onto the equilified cation exchange column. Elute with a linear gradient from 0% to 100% Buffer B over 20 CV. HGH typically elutes as a distinct peak.
- Anion Exchange (e.g., Q Sepharose) can also be used depending on the protein's isoelectric point (pI ~5.3).
- This step separates monomers from aggregates and is the final purification step.
- Column: Superdex 75 16/60 or similar.
- Buffer: 20mM sodium phosphate, pH 7.0, 150mM NaCl.
- Procedure: Load the concentrated protein from the IEX step onto the SEC column. The monomeric HGH (~22 kDa) will elute at a specific volume, separate from higher molecular weight aggregates and lower molecular weight fragments. Collect the monomer peak.
6. Characterization
6.1 Purity and Identity- SDS-PAGE: Run under reducing and non-reducing conditions to verify purity (>95%) and correct disulfide bond formation.
- SEC-HPLC: Re-run the final product on an analytical SEC column to confirm monomeric purity (>98%). Aggregates should be <1%.
- Mass Spectrometry (ESI-MS or MALDI-TOF): Confirm the exact molecular weight of the purified protein (22,125 Da for native somatropin).
- Peptide Mapping: Digest the protein with trypsin and analyze the resulting peptides by LC-MS/MS to confirm the amino acid sequence.
- Cell-Based Proliferation Assay: Use an HGH-responsive cell line, such as Nb2 rat lymphoma cells. Measure the dose-dependent proliferation in response to the purified HGH compared to a reference standard.
- Receptor Binding Assay: Use Surface Plasmon Resonance (SPR, e.g., Biacore) or ELISA to measure the binding affinity (KD) of the HGH to the extracellular domain of its receptor (GHR). The KD should be in the low nanomolar range.
7. Final Formulation and Storage
7.1 Formulation- Buffer: 10mM sodium phosphate, pH 7.0.
- Stabilizers: Add 0.1% (w/v) phenol as a preservative (if for multi-use vials) and 0.9% (w/v) benzyl alcohol or 0.1% (w/v) metacresol as a stabilizer/preservative.
- Tonicity Agent: Add mannitol or glycerol to adjust isotonicity.
- Concentration: Adjust to the final desired concentration (e.g., 5 mg/mL or 10 mg/mL) using ultrafiltration.
- Filter the final formulated solution through a 0.22 µm sterile filter into a sterilized vial under aseptic conditions (laminar flow hood).
- Store the final product at 2-8°C. Avoid freezing.
8. Quality Control Specifications
| Parameter | Specification |
|---|---|
| Appearance | Clear, colorless solution |
| pH | 6.5 - 8.0 |
| Concentration | As labeled (e.g., 5 mg/mL ± 5%) |
| Purity (SEC-HPLC) | >98% monomer |
| Aggregates | <1% |
| Fragments | <1% |
| Identity (Mass Spec) | Confirmed (22,125 Da) |
| Biological Activity | 90-110% of reference standard |
| Endotoxin (LAL test) | <0.5 IU/mL |
| Sterility | Negative (USP <71>) |
| Host Cell Protein (HCP) | <10 ppm |
| Host Cell DNA | <10 pg/dose |
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