Weak promoters to drive selection marker expression: Improvement of cell line development process for therapeutic protein production in CHO-K1 cells.

Chinese Hamster Ovary cells have been widely used as host cells for production of recombinant therapeutic molecules. Cell line development is a decisive step, which must be carried out with an efficient process. In particular, degree of selection stringency is an important parameter for identification of rare, high-producing cell lines. In the CHOZN® CHO K1 platform, selection of top-producing clones is based on puromycin resistance, whose expression is driven by Simian Virus 40 Early (SV40E) promoter. In this study, novel promoters have been identified to drive expression of selection marker. Decrease of transcriptional activity compared to SV40E promoter was confirmed by RT-qPCR. Selection stringency was increased, as seen by decreased surviving rate of transfected mini-pools and longer recovery duration of transfected bulk pools. Several promoters led to a 1.5-fold increase of maximum titer and a 1.3-fold increase of mean specific productivity of the monoclonal antibody over the clone generation. Expression level was maintained stable over long term cultivation. Finally, productivity increase was confirmed on several monoclonal antibodies and fusion proteins. Lowering the strength of promoter for expression of selective pressure resistance is an efficient strategy to increase selection stringency, which can be applied on industrial CHO-based cell line development platforms.

Development of anti-chloro 192 tyrosine HDL apoA-I antibodies for the immunodiagnosis of cardiovascular diseases.

High density lipoproteins (HDL) are considered cardio protective. Apolipoprotein A-I (apoA-I), a major component of HDL helps in reverse cholesterol transport, whose function is greatly affected during atherosclerosis due to oxidation by myeloperoxidase. Amino acid tyrosine residue of apoA-I at position 192 and 166 are sensitive to oxidation by myeloperoxidase resulting in the generation of chlorinated and nitrated apoA-I and they are believed to be present in atherosclerotic plaques and in circulation. These oxidized apoA-I have been suggested as potential indicator(s) of CVD risks in humans. To detect the levels of oxidized apoA-I there is a need for developing monoclonal antibodies (mAbs) with high specificity and sensitivity that could be utilized routinely in clinical immune based assays for blood plasma or for in vivo imaging. In this study, chemically chlorinated apoA-I (chlorinated 192tyrosine- apoA-I) and a short synthetic peptide, containing the corresponding chlorinated tyrosine residue, conjugated to keyhole limpet hemocyanin (KLH) carrier protein were used for immunization. Stable hybridoma clones F7D5 and G11E3 were found to be highly sensitive and reactive towards chlorinated 192tyrosine- apoA-I. Interestingly, these mAbs also displayed positive reaction with atherosclerotic plaques obtained from mouse and human biopsies. In vitro or in vivo diagnostic tests could be developed either by detecting oxidized apoA-I in human plasma or by directly imaging atheroma plaques as both mAbs were shown to stain human atheroma. The anti-chlorinated 192tyrosine- apoA-I mAbs described in this study may have a high diagnostic potential in predicting CVD risks.

Production and Purification of the Native Saccharomyces cerevisiae Hsp12 in Escherichia coli.

Hsp12 is a small heat shock protein produced in many organisms, including the yeast Saccharomyces cerevisiae. It has been described as an indicator of yeast stress rate and has also been linked to the sweetness sensation of wine. To obtain a sufficient amount of protein, we produced and purified Hsp12 without tag in Escherichia coli. A simple fast two-step process was developed using a microplate approach and a design of experiments. A capture step on an anion-exchange salt-tolerant resin was followed by size exclusion chromatography for polishing, leading to a purity of 97%. Thereafter, specific anti-Hsp12 antibodies were obtained by rabbit immunization. An ELISA was developed to quantify Hsp12 in various strains of Saccharomyces cerevisiae. The antibodies showed high specificity and allowed the quantitation of Hsp12 in the yeast. The quantities of Hsp12 measured in the strains differed in direct proportion to the level of expression found in previous studies.

Selective Tuning of Elastin-like Polypeptide Properties via Methionine Oxidation.

We have designed and prepared a recombinant elastin-like polypeptide (ELP) containing precisely positioned methionine residues, and performed the selective and complete oxidation of its methionine thioether groups to both sulfoxide and sulfone derivatives. Since these oxidation reactions substantially increase methionine residue polarity, they were found to be a useful means to precisely adjust the temperature responsive behavior of ELPs in aqueous solutions. In particular, lower critical solution temperatures were found to be elevated in oxidized sample solutions, but were not eliminated. These transition temperatures were found to be further tunable by the use of solvents containing different Hofmeister salts. Overall, the ability to selectively and fully oxidize methionine residues in ELPs proved to be a convenient postmodification strategy for tuning their transition temperatures in aqueous media.

Use of the human hepcidin gene to build a positive-selection vector for periplasmic expression in Escherichia coli.

Recombinant proteins are often produced in the periplasm of Escherichia coli because this facilitates the purification process. The oxidizing environment favors the formation of disulfide bridges. We showed that the periplasmic expression of the human hormone hepcidin 25 (Hep25) fused to the maltose-binding protein (MBP) resulted in cell death. This toxicity was not observed when MBP-Hep25 accumulated in the bacterial cytoplasm, or when Hep25 was addressed to the periplasm without the MBP tag. We then modified the periplasmic expression vector pMALp2E to create pMALp2EH, a positive-selection vector with Hep25 as counterselection gene.

Recombinant production and purification of short hydrophobic Elastin-like polypeptides with low transition temperatures.

Elastin-like polypeptides (ELPs) are biodegradable polymers with interesting physico-chemical properties for biomedical and biotechnological applications. We report herein the recombinant expression of three hydrophobic ELPs (VPGIG)n with variable lengths (n = 20, 40, 60) and sub-ambient transition temperatures. These ELPs were purified from the cytoplasmic soluble fraction of Escherichia coli by inverse transition cycling, and their exact molecular weight was confirmed by various mass spectrometry techniques. Transition temperatures of ELP20, ELP40, and ELP60 were measured at 18.6 °C, 12.4 °C and 11.7 °C, respectively.

Purification process of recombinant monoclonal antibodies with mixed mode chromatography.

An innovative process to purify mAb from CHO cell culture supernatant was developed. This three-step process involved two mixed mode resins and an anion exchange membrane. We used a human IgG mixture to determine the optimal conditions for each purification step. Thereafter, the whole process was evaluated and improved for the purification of a recombinant mAb produced in the supernatant of CHO cells. Once optimized, yield and purity of 88% and 99.9%, respectively were comparable to those obtained in a conventional process based on a capture step using protein A. In addition, aggregates, HCPs and DNA levels in the purified fraction were below regulatory specifications. Then we used mass spectrometry to identify contaminating proteins in the antibody fraction in order to highlight the behavior of HCPs.

Expression and purification of short hydrophobic elastin-like polypeptides with maltose-binding protein as a solubility tag.

Elastin-like polypeptides (ELPs) are biodegradable polymers with interesting physico-chemical properties for biomedical and biotechnological applications. The recombinant expression of hydrophobic elastin-like polypeptides is often difficult because they possess low transition temperatures, and therefore form aggregates at sub-ambient temperatures. To circumvent this difficulty, we expressed in Escherichia coli three hydrophobic ELPs (VPGIG)n with variable lengths (n=20, 40, and 60) in fusion with the maltose-binding protein (MBP). Fusion proteins were soluble and yields of purified MBP-ELP ranged between 66 and 127mg/L culture. After digestion of the fusion proteins by enterokinase, the ELP moiety was purified by using inverse transition cycling. The purified fraction containing ELP40 was slightly contaminated by traces of undigested fusion protein. Purification of ELP60 was impaired because of co-purification of the MBP tag during inverse transition cycling. ELP20 was successfully purified to homogeneity, as assessed by gel electrophoresis and mass spectrometry analyses. The transition temperature of ELP20 was measured at 15.4°C in low salt buffer. In conclusion, this method can be used to produce hydrophobic ELP of low molecular mass.

Production and purification of recombinant human hepcidin-25 with authentic N and C-termini.

Hepcidin was first identified as an antimicrobial peptide present in human serum and urine. It was later demonstrated that hepcidin is the long-sought hormone that regulates iron homeostasis in mammals. Recombinant human Hepcidin-25 (Hepc25) was expressed in Pichia pastoris using a modified version of the pPICZαA vector. Hepc25 was then purified by a simple two-step chromatographic process to obtain 1.9 mg of soluble recombinant human Hepc25 per liter of culture at 96% purity. The sequence of Hepc25 and the presence of four disulfide bridges were confirmed by mass spectrometry analyses, and the recombinant Hepc25 exhibited antibacterial activity. This protocol of production and purification is the first step toward the production of human Hepc25 at a greater scale.

Structure-activity relationship of human liver-expressed antimicrobial peptide 2.

Liver-expressed antimicrobial peptide 2 (LEAP-2) is a 40-residue cationic peptide originally purified from human blood ultrafiltrate. The native peptide contains two disulfide bonds and is unique regarding its primary structure. Its biological role is not known but a previous study showed that chemically synthesized LEAP-2 exhibited in vitro antimicrobial activities against several Gram-positive bacteria. In order to determine its antimicrobial mode of action, we expressed human recombinant LEAP-2 in Escherichia coli. Circular dichroism spectroscopy and nuclear magnetic resonance analyses showed that the structure of the recombinant peptide was identical to that of the chemically synthesized and oxidized LEAP-2, with two disulfide bonds between Cys residues in relative 1-3 and 2-4 positions. Minimal inhibitory concentration (MIC) of the recombinant human LEAP-2 was determined by a conventional broth dilution assay. It was found to be bactericidal against Bacillus megaterium at a 200microM concentration. Interestingly, the linear LEAP-2 had a greater antimicrobial activity with a MIC value of 12.5microM, which was comparable to that of magainin2. SYTOX Green uptake was used to assess bacterial membrane integrity. Linear LEAP-2 and magainin2 permeabilized B. megaterium membranes with the same efficiency, whereas oxidized LEAP-2 did not induce stain uptake. Binding of the peptides to plasmid DNA was evaluated by gel retardation assays. The DNA-binding efficacy of linear LEAP-2 was three times higher than that of the peptide-containing disulfide bridges. Altogether, these results show that the secondary structure of human LEAP-2 has a profound impact on its antibacterial activity.

Temporal gene expression of 3-ketoacyl-CoA reductase is different in high and in low erucic acid Brassica napus cultivars during seed development.

The membrane-bound acyl-CoA elongase complex is a key enzyme responsible for erucoyl-CoA synthesis. Among the four putative genes encoding the four moieties of this complex in Brassica napus seeds, only one has been characterized, the Bn-fae1 gene, which encodes the 3-ketoacyl-CoA synthase. The genes encoding the other enzymes (3-ketoacyl-CoA reductase, 3-hydroxyacyl-CoA dehydratase and trans-2,3-enoyl-CoA reductase) have not been identified. We cloned two 3-ketoacyl-CoA reductase cDNA isoforms, Bn-kcr1 and Bn-kcr2, from B. napus seeds. Their function was identified by heterologous complementation in yeast by restoring elongase activities. The comparison of Bn-kcr mRNA expression in different B. napus tissues showed that the genes were preferentially expressed in seeds and roots. We also investigated the regulation of gene expression in High Erucic Acid Rapeseed (HEAR) and in Low Erucic Acid Rapeseed (LEAR) cultivars during seed development. The co-expression of Bn-fae1 and Bn-kcr observed in HEAR cultivar during seed development was different in LEAR cultivar, suggesting that expression of both genes was directly or indirectly linked.

Chromatographic purification of an insoluble histidine tag recombinant Ykt6p SNARE from Arabidopsis thaliana over-expressed in E. coli.

In order to undertake in plant cell the study of the endoplasmic reticulum (ER)-Golgi apparatus (GA) protein and/or lipid vesicular transport pathway, expressed sequence tag (EST) coding for a homologue to the yeast soluble N-ethylmaleimide-sensitive factor attachment protein receptors (SNAREs) Ykt6p has been cloned in Arabidopsis thaliana by reverse transcription polymerase chain reaction (RT-PCR). The corresponding protein was over-expressed as a recombinant histidine-tag (his-tag) protein in E. coli. Starting from one litter of culture, an ultrasonic homogenization was performed for cell disruption and after centrifugation the Arabidopsis Ykt6p SNARE present in inclusion bodies in the pellet was solubilized. After centrifugation, the clarified feedstock obtained was injected onto an immobilized metal affinity chromatography (IMAC) in presence of 6 M guanidine and on-column refolding was performed. Folded and subsequently purified (94% purity) recombinant protein was obtained with 82% of recovery.