Recombinant Protein Expression - Lab Report Example

Recombinant Protein Expression Introduction. Escherichia coli or the gram-negative bacterium is one of the many heterologous protein system production with a potential to grow rapidly at a density considered being high. It also grows on substrates that are inexpensive, has genetics that are well characterized, and has an increasingly increased number of mutant host strains and cloning vectors. Even though there exist no certainty that a gene recombinant product will be accumulated in the Escherichia coli (E coli) at levels that are high, in biologically active foam, and in full length, a significant magnitude of efforts has been put towards bettering the versatility and performance of the microorganism. This report examined the features of E coli in respect to the expression systems with an emphasis on the limitation number that have been addressed. For a high gene dosage to be achieved, the heterologous cDNAs are normally cloned into replicate plasmids in a fashion that is relaxed and are normally existence at 15-60 copies per cell (Baneyx, 2009). Whenever the additional co-overexpression gene product is needed, ColE1 derivatives are normally put together with plasmids that are compatible and a p15A replication that is maintained at approximately 10 to 12 copies per cell. Under conditions of the laboratory, the multicopy plasmids will be distributed randomly during the division of the cell, and whenever selective pressure are lost at a frequency that is low. This may be due to multimerization (Baneyx, 2009). Whenever there is a high number of copy plasmids, the loss in plasmid can increase tremendously especially when the plasmid bone genes are toxic towards the host or significantly reduce the rate of growth whenever cells are cultivated at densities that are high or in processes that are continuous. These problems can be addressed by using the encoded plasmid antibiotic markers resistance and the supplement growth medium supplemented to do away with the free cells of the plasmid. One key limitation of this approach involves the loss of selective pressure due to the degradation of antibiotics, leakages, or inactivation of the periplasmic detoxifying enzymes into the medium growth and the product contamination (Baneyx, 2009). This drawback could be unacceptable from a regulatory or medical point of view. In this respect, many alternative methods have been established to make sure that the cells that are free from plasmid will not overtake the culture. This means that cloning vectors will be engineered to carry repressors or genes, which leads to cell death whenever there is a loss of plasmid (Cregg, 2000). Even though, this method is proved to be vital, it could place restrictions on the medium growth composition whenever there exist any complication and may introduce a burden metabolism on the cell through requiring transcriptions and translation of additional genes of encoded plasmids. For these problems to be circumnavigated, research has established a host strain having a conditionally essential gene in control of the promoter-operator region and a multicopy companion of the plasmid having the lac operator (Baneyx, 2009). Whenever the LacI receptor protein is titrated by encoded plasmid lac operators, it leads to the gene chromosomal expression and plasmid growth that is selective. It may also bear cells in the medium that is supplemented by the antibiotics. Another different solution to the plasmid instability problem could be a direct insertion of the genes that are heterologous within the E coli chromosomes. Even though, there exist a single vehicle delivery like the bacteriophage in this purpose there has been extremely little emphasis placed on the perceived notion that the dosage of the gene will always be low. In order to gain more insight on the characteristics of the E coli, this experiment was set to investigate the recombinant protein expression. Methodology. Material. The materials used for this experiment include: EcoRi/HindIII cleaned and cut pUC19 vector (V), EcoRi/HindIII cleaned and cut GFP Insert (I), 10 x T4 ligase buffer (B), and Sterile H2O (H2O). Procedure. A ligation reaction was made up. The ligation reaction contained EcoRi/HindIII cleaned and cut GFP Insert, EcoRi/HindIII cleaned and cut pUC19 vector (V), Sterile H2O, and 10 x T4 ligase buffer. The reaction was incubated at room temperature for the duration of thirty minutes. 100 μL of BL21 E coli competent cells were defrost on the ice. 10μL ligation reaction was added to the competent cells on ice and incubated for the duration of thirty minutes on ice. The transformation mixture was taken out of the ice and shock heated at 42 degrees Celsius for about 75 seconds. Next, the specimen was immediately returned to ice for a period of two minutes. The cells were plate out on the selective plates of media (40μgml-1 x gal, 1.5%LB Agar, 0.1 mM IPTG, and 50μg mL-1 ampicillin. After this, the transformation was allowed to dry on plates and incubated agar up at thirty seven degrees Celsius for the duration of about 12 to 18 hours. Additionally, a 2 x 5 ml LB + 50μgmL-1 ampicillin was set up in 30 ml tubes that were sterile. The 1 x white individual colony and 1 x Blue individual colony were picked up and inoculated in separate tubes. The colonies were incubated inside a shaking incubator over night at thirty seven degrees Celsius and 220rpm. Next, a 2 x 60 mL sterile LB was prewarmed in a conical flast of 250mL at thirty seven degrees Celsius. Ampicillin was added to the final concentration having 50μgmL-1 ampicillin aseptically. 1mL of media was removed and placed in the cuvette to function as blank. A 600 μL overnight culture of the single colonies were added to separate flasks. The flasks were return to the incubator and incubated at thirty seven degrees Celsius and at 200rmp. The spectrophotometer was blanked at 600nm against media. At intervals of 45 minutes, the samples were removed aseptically from the flasks. 1 x 1 mL of each flask was removed to add to a clean cuvette that is fresh, and a 1 x 1 mL was added to into a clean Eppendorf. OD600nm of the culture was measured in the cuvetteand recorded the results for the growth curve. When the cultures reached the OD600nm of 0.5, IPTG was added to the last concentration 1 mM from the solution stock. The samples were spinned down in the Eppendorf tube at a maximum speed inside the microcentrifuge for the duration of five minutes. The centrifuge was kept in a balanced position before the spinning began. The supernatant was removed, and the pellet retained. The pellet was resuspended in the 200 μL cell buffer lysis. The resuspended was then frozen at a temperature of negative twenty degrees until the following day. The sampling process kept on up to the time when OD 600nm failed to raise for the two successive samples. Results. All the collected data was recorded in table 1. Table 1. From table 1, a graph of the observations versus the specific time was plotted. Graph 1: A graph of observation against time. Discussion. E coli are an expression host in which the DNA is always introduced in the expression plasmid vector. This experiment display a clear method of overexpression in E coli. From the observation, it is evidenced that the technique worked through increasing the number of the gene copies. In this case, the binding strength of the region of the promoter was increased to help the transcription. In this experiment, a sequence of DNA was cloned into an increased copy plasmid number having the lac promoter that was transformed into the E coli (Kost, 2005). The IPTG addition has an effect of activating the promoter lac making the bacteria express the required protein. In this process, the region of the DNA which flanks the promoters core has a vital role in finding the efficiency of transcription. The upstream elements in some promoters bacteria are A + T sequences rich hence increase the transcription through their interaction with the α subunits of the RNA polymerase. From the experiment, it is evidenced that the E coli m RNAs are unstable if their half lives range between thirty seconds and twenty minutes. The prime enzyme that is involved in the mRNA degradation are the 3’-5’ exonucleases. This include the RNase II and the phosphorylase polynucleotide, and the RNase endonuclease (Cregg, 2000). The catalyst trait of the RNase E is positioned at the amini terminus of protein, and the carboxy-terminus acts as a scaffold in the assembly of the RNA high efficient degradasome involving PNPase, the glycolytic enolase enzyme, and the DEAD-boxRNA Rhlb helicase (Rosser, 2005). On the other hand, the heterologous overproduction of proteins in the E coli’s cytoplasm is normally followed by their segregation and misfolding into aggregates that are insoluble referred to as inclusion bodies (Malys, 2011). Even though, the formation of the inclusion body considerably simplify the purification of protein, there is no certainty that the in vitro refolding could produce increased quantities of products that are biologically active. The protein proteolytic and folding degradation are always associated since catabolism in an appropriate way of conserving the cellular resources through recycling the damaged, or improperly folded proteins into their amino acids constituent. In the E.coli cytoplasm, may degradation steps are normally done by five ATP-dependent Hsps (Cregg, 2000). CIpXp and CIpAP are proteases components, which share a similar subunit degradation but poses vared ATPase subunits regulatory (Rosser, 2005). They are known to bind substrates in the manner of chaperone and utilize the hydrolysis to give the mini-proteasome structures food. It is also worth noting that the polypeptides used for exports are normally synthesized as those proteins that have amino terminal sequence signals. During translocation, they are cleaved through the inner membrane that is linked to the peptidase leader and the active sites of the periplasm face (Malys, 2011). In this case, a typical sequence signal has 18 to 30 amino acids and more than two basicresidues at the terminus of the amino and a hydrophilic carboxyl motif terminus. A number of sequence signals obtained from secretory proteins that occur naturally is in support of the efficient heterologous translocation of the polypeptides along the internal membrane whenever they are fused to the terminal amino acid. Conclusion. Different efforts towards the understanding of the interaction and regulation of the gene's cell products and the existence of the new genetic tool have made the E coli an attractive host for producing heterologous proteins (Malys, 2011). The idea that minimum information is to date exploited for experimental reasons and that key aspects of E coli physiology remain uncovered continue to motivate the optimization of this organism for the expression of protein. In this experiment, all the objectives of the experiment were achieved. The experimental data was slightly different from the theoretical values due to the experimental errors. Some of the error were due to air resistance, faultiness of the equipments, and wrong calculations. References. Baneyx, F., 2009. Recombinant Escherichia coli protein expression. Currs. Opin. Biotechnol. 10 (5): 411–21. Cregg, M., 2000. Recombinant Pichia pastoris protein expression. Mols. Biotechnol. 16 (1): 23–52. Malys, N., 2011. Saccharomyces cerevisiae protein production for systems biology study. Method Enzymol. 500: 197–212. Kost, A., 2005. Baculovirus as vectors versatile for protein expression cells. Nat. Biotechnol. 23 (5): 567–75. Rosser, M., 2005. Rapid mammalian protein system expression. New York: Jack and Sons Publishers. Read More