This work was financially supported by the grants K22AI099165 (AWB), P41GM103390 (KWM) and P01GM107012 (KWM) from the National Institutes of Health, and by funds from the Roy J. Carver Department of Biochemistry, Biophysics &#38; Molecular Biology at Iowa State University. The content of this work is solely the responsibility of the authors and does not necessarily represent the official views of the NIH.

This protocol is sufficient for expression using either HEK293F or HEK293S cells.&#160;
1. Cell Establishment&#160;
<ol>
	<li>Culture Inoculation 
	Note: All culture manipulation procedures must be carried in a BSL-2 facility and each item brought into the biosafety cabinet must be sterilized by spraying with a 70% ethanol in water solution.
	<ol>
		<li>Operate the incubator shaker at 135 rpm, 80% humidity and at 8.0% CO2 and 37 &#176;C. Turn &#34;on&#34; the UV lamp of the biosafety cabinet at l...

All authors declare no competing financial interests in this manuscript.

This protocol illustrates protein expression via the transient transfection of HEK293F or S cells. The optimal transfection conditions established in the Barb and Moremen labs employ a critical combination of cell density and reagent concentrations to achieve high efficiency transfection. Critical considerations when implementing this protocol include: maintaining a stable culture prior to transfection (with consistent culture doubling times); transfection of actively growing cells (achieved by diluting cells to 1 &#215;...

An erratum was issued for:&#160;<a href="https://www.jove.com/t/53568">High Yield Expression of Recombinant Human Proteins with the Transient Transfection of HEK293 Cells in Suspension</a>. The Authors section was updated. from:
Ganesh P. Subedi1 
Roy W. Johnson2 
Heather A. Moniz2 
Kelley W. Moremen2 
Adam Barb1 
1The Roy J. Carver Department of Biochemistry, Biophysics and Molecular Biology, Iowa State University 
2Complex Carbohydrate Research Center, University of Georgia
to
Ganesh P. Subedi1 
Roy W. Johnson2 
Heather A. Moniz2 
Kelley W. Moremen2 
Adam W. Barb1 
1The Roy J. Carver Department of Biochemistry, Biophysics and Molecular Biology, Iowa State University 
2Complex Carbohydrate Research Center, University of Georgia

An erratum was issued for:&#160;<a href="https://www.jove.com/t/53568">High Yield Expression of Recombinant Human Proteins with the Transient Transfection of HEK293 Cells in Suspension</a>. The Authors section was updated.

Erratum: High Yield Expression of Recombinant Human Proteins with the Transient Transfection of HEK293 Cells in Suspension

Producing high yields of appropriately folded and post-translationally modified human proteins for detailed analysis of structure and function remains a significant challenge. A large number of expression systems are available that produce recombinant proteins with native-like function and behavior. Bacterial expression systems, predominantly Escherichia coli strains, represent the most accessible and commonly used tools in the research arena, due to the simplicity of these expression systems, though yeast, plant, insect and mammalian systems are also described1-4. However, the majority of these systems are incapable of appropriate post-translational modification of the target proteins. A fundamental interest of the Barb and Moremen laboratories is producing eukaryotic proteins with appropriate glycosylation. Many human proteins require appropriate glycosylation for proper function (see5).
The eukaryotic glycosylation machinery is extensive and capable of making a diverse range of modifications, including both asparagine(N)- and serine/threonine(O)-linked complex glycans6. It is estimated that &#62;50% of human proteins are N-glycosylated7. Glycans are essential components of many proteins including therapeutic monoclonal antibodies, erythropoietin, and blood clotting factors like factor IX, to name a few. Though multiple methods exist to prepare appropriately N-glycosylated proteins and range from purely synthetic8-10, to chemoenzymatic11-14 or recovery from engineered recombinant systems15-20, not surprisingly, human expression systems have thus far proven to be the most robust methods for generating human proteins.
Many therapeutic human glycoproteins are produced in recombinant systems using mammalian cells. Systems of note are the Chinese Hamster Ovary (CHO), mouse myeloma (NS0), Baby Hamster Kidney (BHK), Human Embryonic Kidney (HEK-293) and human retinal cell lines that are employed in adhesion or suspension culture for protein production4,21,22. However, mammalian protein expression systems have required the generation of stable cell lines, expensive growth media and substrate assisted transfection procedures23.
Mammalian cell transfection is achieved with the aid of numerous agents including calcium phosphates24,25, cationic polymers (DEAE-dextran, polybrene, polylysine, polyethylimine (PEI)) or positively charged cationic liposomes26-29. PEI is a polycationic, charged, linear or branched polymer (25 kDa)26 that forms a stable complex with DNA and is endocytosed. Upon acidification of the endosome, PEI is thought to swell, leading to the rupture of endosomes and release of the DNA into the cytoplasm26,30.
Until recently, transient transfection in suspension culture was carried by prior DNA/PEI complex formation followed by addition to the cell culture29. However, W&#252;rm and coworkers reported a highly efficient protocol optimized for recombinant protein production in HEK293 cells that formed a DNA/PEI complex in situ31,32. This avoided preparation, sterilization of the complex, and buffer exchange into a culture medium. Further optimization by including expression-enhancing plasmids led to significant yield increases33. Herein is a method that builds upon these advances and is broadly applicable. Expression conditions may also be altered to impact the N-glycan composition.
The HEK293S cell line, with a gene deletion that halts N-glycan processing at an intermediate stage, leads to the expression of proteins with uniform N-glycans consisting of 2 N-acetylglucosamine residues plus five mannose residues (Man5GlcNAc2)34,35. These cells lack the N-acetylglucosaminyl transferase I (GntI) gene which is required for downstream N-glycan processing36,37. The use of glycosyltransferase inhibitors including kifunensine, sialic acid analogs and the fucose analog and 2-deoxy-2-fluoro-fucose has similar effects and limits N-glycan processing38-41.
The protocol reported here uses the pGEn2 vector as shown in Figure 142,43, PEI assisted transient transfection into mammalian cells lines (HEK293F or HEK293S cells), and the recovery of high yields of appropriately glycosylated protein. This system is robust and can accommodate various factors including isotope labeling and glycan engineering for the production of large titers of recombinant proteins.

<table>
	<tbody>
		<tr>
			<td>Biosafety cabinet&#160;</td>
			<td>NuAire, Inc.</td>
			<td>CellGard ES NU-S475-400</td>
			<td>Class II, Type A2 Biological Safety Cabinet</td>
		</tr>
		<tr>
			<td>Incubation shaker</td>
			<td>INFORS HT</td>
			<td></td>
			<td>Multitron Cell&#160;</td>
		</tr>
		<tr>
			<td>Medium A: FreeStyle Expression Medium&#160;</td>
			<td>Life Technologies</td>
			<td>12338-018</td>
			<td></td>
		</tr>
		<tr>
			<td>Medium B: ExCell 293 Serum-Free Medium&#160;</td>
			<td>SIGMA</td>
			<td>14571C&#160;</td>
			<td></td>
		</tr>
		<tr>
			<td>125 Erlenmeyer Flask with Vented Cap</td>
			<td>Corning Incorporated/Life Sciences</td>
			<td>431143</td>
			<td></td>
		</tr>
		<tr>
			<td>250 Erlenmeyer Flask with Vented Cap</td>
			<td>Corning Incorporated/Life Sciences</td>
			<td>431144</td>
			<td></td>
		</tr>
		<tr>
			<td>FreeStyle HEK 293F Cells</td>
			<td>Life Technologies</td>
			<td>R790-07</td>
			<td></td>
		</tr>
		<tr>
			<td>1 ml Disposable serological pipette</td>
			<td>Fisher Scietific</td>
			<td>13-676-10B</td>
			<td></td>
		</tr>
		<tr>
			<td>10 ml Disposable serological pipette</td>
			<td>Fisher Scietific</td>
			<td>13-676-10J</td>
			<td></td>
		</tr>
		<tr>
			<td>25 ml Disposable serological pipette</td>
			<td>Fisher Scietific</td>
			<td>13-676-10K</td>
			<td></td>
		</tr>
		<tr>
			<td>Pipettor (Pipet-Aid XP)</td>
			<td>Drummond Scientific</td>
			<td>161263</td>
			<td></td>
		</tr>
		<tr>
			<td>Trypan Blue Solution&#160;</td>
			<td>Thermo Scientific&#160;</td>
			<td>SV30084.01</td>
			<td></td>
		</tr>
		<tr>
			<td>Counting slides&#160;</td>
			<td>Bio-Rad</td>
			<td>145-0011</td>
			<td></td>
		</tr>
		<tr>
			<td>TC20 Automated Cell Counter&#160;</td>
			<td>Bio-Rad&#160;</td>
			<td>145-0102</td>
			<td></td>
		</tr>
		<tr>
			<td>Polyethylenimine (PEI)</td>
			<td>Polysciences Inc.</td>
			<td>23966</td>
			<td>Prepare stock solution at a concentration of 1 mg/ml in a buffer containing 25 mM 4-(2-hydroxyethyl)-1-piperazineethanesulfonic acid (HEPES) and 150 mM NaCl (pH 7.5). Dissolve PEI completely; sterilize through 0.22 &#956;M syringe filter and store at -20 &#176;C.</td>
		</tr>
		<tr>
			<td>4-(2-hydroxyethyl)-1-piperazineethanesulfonic acid (HEPES)</td>
			<td>EMD Chemicals Inc.</td>
			<td>7365-45-9</td>
			<td></td>
		</tr>
		<tr>
			<td>25 mm Syringe Filter, 0.22 &#956;M</td>
			<td>Fisher Scietific</td>
			<td>09-719A</td>
			<td></td>
		</tr>
		<tr>
			<td>Trisaminomethane (Tris base)</td>
			<td>Fisher Scietific</td>
			<td>BP152-1</td>
			<td></td>
		</tr>
		<tr>
			<td>XL1-Blue</td>
			<td>Stratagene</td>
			<td>222249</td>
			<td></td>
		</tr>
		<tr>
			<td>Trypton</td>
			<td>Fisher Scietific</td>
			<td>BP1421-2</td>
			<td></td>
		</tr>
		<tr>
			<td>Yeast extract</td>
			<td>Fluka Analytical&#160;</td>
			<td>92144</td>
			<td></td>
		</tr>
		<tr>
			<td>Sodium chloride</td>
			<td>BDH chemicals</td>
			<td>BDH8014</td>
			<td></td>
		</tr>
		<tr>
			<td>Plasmid Purification Kit</td>
			<td>QIAGEN</td>
			<td>12145</td>
			<td></td>
		</tr>
		<tr>
			<td>Valproic (VPA)</td>
			<td>SIGMA</td>
			<td>P4543</td>
			<td>Prepare stock solution of 220 mM&#160; in water, sterilize by passage through a sterile 0.22 mm filter and store at -20 &#176;C</td>
		</tr>
		<tr>
			<td>Corning&#63720; 250 mL Centrifuge Tube&#160;</td>
			<td>Corning Incorporated/Life Sciences</td>
			<td>430776</td>
			<td></td>
		</tr>
		<tr>
			<td>Centrifuge</td>
			<td>Thermo Scientific&#160;</td>
			<td>EW-17707-65</td>
			<td></td>
		</tr>
		<tr>
			<td>Protein A-Sepharose column</td>
			<td>SIGMA</td>
			<td>P9424</td>
			<td></td>
		</tr>
		<tr>
			<td>Ni-NTA superflow</td>
			<td>QIAGEN</td>
			<td>30430</td>
			<td></td>
		</tr>
		<tr>
			<td>3-(N-morpholino)propanesulfonic acid (MOPS)</td>
			<td>Fisher Scietific</td>
			<td>BP308-500</td>
			<td></td>
		</tr>
		<tr>
			<td>Glycine</td>
			<td>Fisher Scietific</td>
			<td>BP381-500</td>
			<td></td>
		</tr>
		<tr>
			<td>10 kDa molecular weight cut-off Amicon&#174; Ultra centrifugal filters&#160;</td>
			<td>Millipore</td>
			<td>UFC901096</td>
			<td></td>
		</tr>
		<tr>
			<td>Sodium dodecyl sulfate</td>
			<td>ALDRICH</td>
			<td>L3771</td>
			<td></td>
		</tr>
		<tr>
			<td>Beta-mercaptoethanol</td>
			<td>ALDRICH</td>
			<td>M6250</td>
			<td></td>
		</tr>
		<tr>
			<td>Glycerol</td>
			<td>SIGMA</td>
			<td>G5516</td>
			<td></td>
		</tr>
		<tr>
			<td>Precision Plus Protein All Blue Standards</td>
			<td>Bio-Rad</td>
			<td>161-0373</td>
			<td></td>
		</tr>
		<tr>
			<td>Acetic Acid, Glacial&#160;</td>
			<td>Fisher Scietific</td>
			<td>64-19-7</td>
			<td></td>
		</tr>
		<tr>
			<td>coomassie brilliant blue&#160;</td>
			<td>Bio-Rad&#160;</td>
			<td>161-0406</td>
			<td></td>
		</tr>
		<tr>
			<td>MALDI-TOFMS Voyager-DE PRO&#160;</td>
			<td>Applied Biosystems</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>15N labeled L-Tyrosine</td>
			<td>ALDRICH</td>
			<td>332151</td>
			<td></td>
		</tr>
		<tr>
			<td>15N labeled L-Lysine</td>
			<td>ALDRICH</td>
			<td>592900</td>
			<td></td>
		</tr>
		<tr>
			<td>Unlabeled L-Phenylalanine</td>
			<td>SIGMA-ALDRICH</td>
			<td>P2126</td>
			<td></td>
		</tr>
		<tr>
			<td>13C6-Glucose</td>
			<td>ALDRICH</td>
			<td>389374</td>
			<td></td>
		</tr>
		<tr>
			<td>2-deoxy-2-fluoro-l-fucose&#160;</td>
			<td>SANTA CRUZ Biotechnology</td>
			<td>sc-283123</td>
			<td></td>
		</tr>
	</tbody>
</table>

high yield expression of recombinant human proteins with the transient transfection of hek293 cells in suspension

The art of producing recombinant proteins with complex post-translational modifications represents a major challenge for studies of structure and function. The rapid establishment and high recovery from transiently-transfected mammalian cell lines addresses this barrier and is an effective means of expressing proteins that are naturally channeled through the ER and Golgi-mediated secretory pathway. Here is one protocol for protein expression using the human HEK293F and HEK293S cell lines transfected with a mammalian expression vector designed for high protein yields. The applicability of this system is demonstrated using three representative glycoproteins that expressed with yields between 95-120 mg of purified protein recovered per liter of culture. These proteins are the human Fc&#947;RIIIa and the rat &#945;2-6 sialyltransferase, ST6GalI, both expressed with an N-terminal GFP fusion, as well as the unmodified human immunoglobulin G1 Fc. This robust system utilizes a serum-free medium that is adaptable for expression of isotopically enriched proteins and carbohydrates for structural studies using mass spectrometry and nuclear magnetic resonance spectroscopy. Furthermore, the composition of the N-glycan can be tuned by adding a small molecule to prevent certain glycan modifications in a manner that does not reduce yield.

High-level protein expression and purity
This optimized expression system generated a high yield of glycosylated proteins. A typical pattern is shown in the expression of IgG1-Fc (Figure 1). In this case, Day 0 is the transfection day followed by Day 1 (dilution) and subsequent culture days up to Day 5. Protein expression is analyzed using the soluble expression fraction in the crude medium. A very small amount ...

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High Yield Expression of Recombinant Human Proteins with the Transient Transfection of HEK293 Cells in Suspension

Laboratory-scale production of eukaryotic proteins with appropriate post-translational modification represents a significant barrier. Here is a robust protocol with rapid establishment and turnaround for protein expression using a mammalian expression system. This system supports selective amino acid, selective labeling of proteins and small molecule modulators of glycan composition.

The art of producing recombinant proteins with complex post-translational modifications represents a major challenge for studies of structure and ...

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29.3K Views.  Iowa State University. Laboratory-scale production of eukaryotic proteins with appropriate post-translational modification represents a significant barrier. Here is a robust protocol with rapid establishment and turnaround for protein expression using a mammalian expression system. This system supports selective amino acid, selective labeling of proteins and small molecule modulators of glycan composition.