Expression, purification, and characterization of authentic mouse prolactin obtained in Escherichia coli periplasmic space

Synthesis of Human Bone Morphogenetic Protein-2 (hBMP-2) in E. coli Periplasmic Space: Its Characterization and Preclinical Testing

Human BMP-2, a homodimeric protein that belongs to the TGF- β family, is a recognized osteoinductor due to its capacity of inducing bone regeneration and ectopic bone formation. The administration of its recombinant form is an alternative to autologous bone grafting. A variety of E. coli-derived hBMP-2 has been synthesized through refolding of cytoplasmic inclusion bodies. The present work reports the synthesis, purification, and characterization of periplasmic hBMP-2, obtained directly in its correctly folded and authentic form, i.e., without the initial methionine typical of the cytoplasmic product that can induce undesired immunoreactivity. A bacterial expression vector was constructed including the DsbA signal peptide and the cDNA of hBMP-2. The periplasmic fluid was extracted by osmotic shock and analyzed via SDS-PAGE, Western blotting, and reversed-phase high-performance liquid chromatography (RP-HPLC). The purification was carried out by heparin affinity chromatography, followed by high-performance size-exclusion chromatography (HPSEC). HPSEC was used for qualitative and quantitative analysis of the final product, which showed >95% purity. The classical in vitro bioassay based on the induction of alkaline phosphatase activity in myoblastic murine C2C12 cells and the in vivo bioassay consisting of treating calvarial critical-size defects in rats confirmed its bioactivity, which matched the analogous literature data for hBMP-2.

Influence of the expression vector and its elements on recombinant human prolactin synthesis in Escherichia coli; co-directional orientation of replication and transcription is highly critical

The aim of the present work was to define a bacterial expression system that is particularly efficient for the synthesis of recombinant human prolactin (hPRL). In previous work, based on experiments that were basically carried out in parallel with the present ones, the synthesis of rec-hPRL by the p1813-hPRL vector in E. coli HB2151 was >500 mg/L, while it was much lower here (2.5-4-fold), in the RB791 and RRI strains. The highest positive influence on rec-hPRL synthesis was due to the transcription-replication co-orientation of hPRL cDNA and the ori/antibiotic resistance gene, responsible for up to a ~ 5-6-fold higher expression yield. In conclusion, this work confirmed that each bacterial strain of E. coli has a genetic background that can allow a different level of heterologous protein synthesis. The individual study of each element indicated that its action critically depends on the reading orientation in which it is located inside the vector: co-directional orientation of replication and transcription, in fact, greatly increased the level of rec-hPRL expression.

Harnessing the potential of bacterial oxidative folding to aid protein production

Protein folding is central to both biological function and recombinant protein production. In bacterial expression systems, which are easy to use and offer high protein yields, production of the protein of interest in its native fold can be hampered by the limitations of endogenous posttranslational modification systems. Disulfide bond formation, entailing the covalent linkage of proximal cysteine amino acids, is a fundamental posttranslational modification reaction that often underpins protein stability, especially in extracytoplasmic environments. When these bonds are not formed correctly, the yield and activity of the resultant protein are dramatically decreased. Although the mechanism of oxidative protein folding is well understood, unwanted or incorrect disulfide bond formation often presents a stumbling block for the expression of cysteine-containing proteins in bacteria. It is therefore important to consider the biochemistry of prokaryotic disulfide bond formation systems in the context of protein production, in order to take advantage of the full potential of such pathways in biotechnology applications. Here, we provide a critical overview of the use of bacterial oxidative folding in protein production so far, and propose a practical decision-making workflow for exploiting disulfide bond formation for the expression of any given protein of interest.

Periplasmic synthesis and purification of the human prolactin antagonist Δ1-11-G129R-hPRL

The human prolactin antagonist Δ_1-11-G129R-hPRL is a 21.9 kDa recombinant protein with 188 amino acids that downregulates the proliferation of a variety of cells expressing prolactin receptors. Periplasmic expression of recombinant proteins in E. coli has been considered an option for obtaining a soluble and correctly folded protein, as an alternative to cytoplasmic production. The aim of this work was, therefore, to synthesize for the first time, the Δ_1-11-G129R-hPRL antagonist, testing different activation temperatures and purifying it by classical chromatographic techniques. E. coli BL21(DE3) strain was transformed with a plasmid based on the pET25b( +) vector, DsbA signal sequence and the antagonist cDNA sequence. Different doses of IPTG were added, activating under different temperatures, and extracting the periplasmic fluid via osmotic shock. The best conditions were achieved by activating at 35 °C for 5 h using 0.4 mM IPTG, which gave a specific expression of 0.157 ± 0.015 μg/mL/A₆₀₀ at a final optical density of 3.43 ± 0.13 A₆₀₀. Purification was carried out by nickel-affinity chromatography followed by size-exclusion chromatography, quantification being performed via high-performance size-exclusion chromatography (HPSEC). The prolactin antagonist was characterized by SDS-PAGE, Western blotting, reversed-phase high-performance liquid chromatography (RP-HPLC) and MALDI-TOF–MS. The final product presented > 95% purity and its antagonistic effects were evaluated in vitro in view of potential clinical applications, including inhibition of the proliferation of cancer cells overexpressing the prolactin receptor and specific antidiabetic properties, taking also advantage of the fact that this antagonist was obtained in a soluble and correctly folded form and without an initial methionine.

Expression of glycosylated human prolactin in HEK293 cells and related N-glycan composition analysis

Prolactin (PRL) is a hormone produced by the pituitary gland with innumerable functions, such as lactation, reproduction, osmotic and immune regulation. The present work describes the synthesis of hPRL in human embryonic kidney (HEK293) cells, transiently transfected with the pcDNA-3.4-TOPO^® vector carrying the hPRL cDNA. A concentration of ~ 20 mg/L, including glycosylated (G-hPRL) and non-glycosylated (NG-hPRL) human prolactin, was obtained, with ~ 19% of G-hPRL, which is higher than that observed in CHO-derived hPRL (~ 10%) and falling within the wide range of 5–30% reported for pituitary-derived hPRL. N-Glycoprofiling analysis of G-hPRL provided: (i) identification of each N-glycan structure and relative intensity; (ii) average N-glycan mass; (iii) molecular mass of the whole glycoprotein and relative carbohydrate mass fraction; (iv) mass fraction of each monosaccharide. The data obtained were compared to pituitary- and CHO-derived G-hPRL. The whole MM of HEK-derived G-hPRL, determined via MALDI–TOF-MS, was 25,123 Da, which is 0.88% higher than pit- and 0.61% higher than CHO-derived G-hPRL. The main difference with the latter was due to sialylation, which was ~ sevenfold lower, but slightly higher than that observed in native G-hPRL. The “in vitro” bioactivity of HEK-G-hPRL was ~ fourfold lower than that of native G-hPRL, with which it had in common also the number of N-glycan structures.

Suppression of Prolactin Secretion Partially Explains the Antidiabetic Effect of Bromocriptine in ob/ob Mice

Previous studies have shown that bromocriptine mesylate (Bromo) lowers blood glucose levels in adults with type 2 diabetes mellitus; however, the mechanism of action of the antidiabetic effects of Bromo is unclear. As a dopamine receptor agonist, Bromo can alter brain dopamine activity affecting glucose control, but it also suppresses prolactin (Prl) secretion, and Prl levels modulate glucose homeostasis. Thus, the objective of the current study was to investigate whether Bromo improves insulin sensitivity via inhibition of Prl secretion. Male and female ob/ob animals (a mouse model of obesity and insulin resistance) were treated with Bromo and/or Prl. Bromo-treated ob/ob mice exhibited lower serum Prl concentration, improved glucose and insulin tolerance, and increased insulin sensitivity in the liver and skeletal muscle compared with vehicle-treated mice. Prl replacement in Bromo-treated mice normalized serum Prl concentration without inducing hyperprolactinemia. Importantly, Prl replacement partially reversed the improvements in glucose homeostasis caused by Bromo treatment. The effects of the Prl receptor antagonist G129R-hPrl on glucose homeostasis were also investigated. We found that central G129R-hPrl infusion increased insulin tolerance of male ob/ob mice. In summary, our findings indicate that part of Bromo effects on glucose homeostasis are associated with decrease in serum Prl levels. Because G129R-hPrl treatment also improved the insulin sensitivity of ob/ob mice, pharmacological compounds that inhibit Prl signaling may represent a promising therapeutic approach to control blood glucose levels in individuals with insulin resistance.

High production and optimization of the method for obtaining pure recombinant human prolactin

Prolactin is a pituitary hormone that is involved diverse physiological functions, such as lactation, reproduction, metabolism, osmoregulation, immunoregulation, and behavior. Its level of glycosylation is low in vivo, which favors its expression in bacterial systems. In the present work recombinant human prolactin (rec-hPRL) was expressed from the p1813-hPRL vector in Escherichia coli strain in inclusion bodies with 530.67 mg of rec-hPRL per liter of induced bacterial culture. The solubilization and renaturation of rec-hPRL followed by two methods described in the literature for this protein: one with detergent and basic pH, and other urea and dialyses was done by studying. The protocol with detergent/basic pH was not successful, whereas protocol with urea/dialyses was obtained pure protein and this was optimized. Rec-hPRL was obtained in a soluble, pure and active form, when the sample was 8-fold concentrated in the solubilization phase, allowing 33% recovery, 3-fold more that the original method. The pure protein was obtained with 38.37 i. u./mg activity, which is three times greater than that of the PRL standard from the WHO. In conclusion, this work obtained the highest production of rec-hPRL, and concentrating the sample eight times in the solubilization stage was decisive for obtaining a highly concentrated, active protein for future work.

Determination of recombinant Interferon-α2 in E. coli periplasmic extracts by reversed-phase high-performance liquid chromatography

Reversed-phase high-performance liquid chromatography (RP-HPLC) has been used to analyze Interferon α-2 (IFN-α2) as a pure protein or as a pharmaceutical preparation: a method for analyzing periplasmic IFN-α2 directly in osmotic shock extract has, however, never been reported. This work describes an RP-HPLC methodology for the qualitative and quantitative analysis of human IFN-α2a and IFN-α2b directly in bacterial periplasmic extracts or in purified preparations. The analytical method has been set up and validated for accuracy, precision, linearity, sensitivity and specificity. A recovery test indicated an average bias of ∼1%, intra-day and inter-day quantitative determinations presented relative standard deviations always≤5%, while the working sensitivity was of ∼0.3μg of IFN-α2 (RSD=5%). The method proved to be suitable for detecting and quantifying also glycosylated and oxidized forms and N-methionylated IFN-α2 molecules, it was, however, not able to distinguish between IFN-α2a and IFN-α2b. This rapid methodology allows the application of RP-HPLC as a powerful tool to monitor the production yield and quality of IFN-α2 in osmotic shock fluids, right after, or even during the fermentation process.

Expression, purification and characterization of the authentic form of human growth hormone receptor antagonist G120R-hGH obtained in Escherichia coli periplasmic space

The human growth hormone receptor antagonist G120R-hGH precludes dimerization of GH and prolactin receptors and consequently JAK/STAT signaling. Some modifications in this antagonist resulted in a drug specific for the GH receptor, called Pegvisomant (Somavert^®). However, the original G120R-hGH is usually synthesized in bacterial cytoplasm as inclusion bodies, not being a commercial product. The present work describes the synthesis and characterization of G120R-hGH secreted into bacterial periplasm and obtained with a vector based on a constitutive lambda-PL promoter. This antagonist can be useful for studies aiming at investigating the effects of a simultaneous inhibition of GH and prolactin signaling, as a potential anti-tumoral or anti-diabetic compound. G120R-hGH, synthesized using the W3110 E. coli strain, showed a yield of 1.34 ± 0.24 μg/ml/A₆₀₀ (∼0.79 mg G120R-hGH/g of wet weight cells) after cultivation at 30 °C up to 3 A₆₀₀ units and induction at 37 °C, for 6 h, with final 4.3 ± 0.3 A₆₀₀. A laboratory scale purification was carried out using three chromatographic steps with a total yield of 32%, reaching 98% purity. The obtained protein was characterized by SDS-PAGE, Western Blotting, Mass spectrometry, RP-HPLC, HPSEC and in vitro proliferation bioassay. The proliferation assay, based on Ba/F3-LLP cells, shows that G120R-hGH (100 ng/ml) significantly inhibited (64%) the proliferative action of hGH (1 ng/ml). This is the first time that G120R-hGH is synthesized in bacterial periplasmic space and therefore correctly folded, without the initial methionine. The reasons for a divergent efficacy for antagonizing hGH versus hPRL is currently unknown and deserves further investigation.

N-glycoprofiling analysis in a simple glycoprotein model: a comparison between recombinant and pituitary glycosylated human prolactin

Human prolactin (hPRL) is a polypeptide hormone occurring in the non-glycosylated (NG-hPRL) and glycosylated (G-hPRL) forms, with MM of approximately 23 and 25kDa, respectively. It has a single, partially occupied N-glycosylation site located at Asn-31, which makes it a particularly simple and interesting model for glycosylation studies. The bioactivity of G-hPRL is lower than that of NG-hPRL (by ca. 4-fold) and its physiological function is not clear. However, carbohydrate moieties generally play important roles in the biosynthesis, secretion, biological activity, and plasma survival of glycohormones and can vary depending on the host cell. The main objective of this study was to determine the N-glycan structures present in native, pituitary G-hPRL and compare them with those present in the recombinant hormone. To obtain recombinant G-hPRL, genetically modified Chinese hamster ovary cells (CHO), adapted to growth in suspension, were treated with cycloheximide, thus increasing the glycosylation site occupancy from 5.5% to 38.3%, thereby facilitating G-hPRL purification. CHO cell-derived G-hPRL (CHO-G-hPRL) was compared to pituitary G-hPRL (pit-G-hPRL) especially with regard to N-glycoprofiling. Among the main differences found in the pituitary sample were an extremely low presence of sialylated (1.7%) and a high percentage of sulfated (74.0%) and of fucosylated (90.5%) glycans. A ∼6-fold lower in vitro bioactivity and a higher clearance rate in mice were also found for pit-G-hPRL versus CHO-G-hPRL. N-Glycan profiling proved to be a useful and accurate methodology also for MM and carbohydrate content determination for the two G-hPRL preparations, in good agreement with the values obtained directly via MALDI-TOF-MS.