Following the harvesting and re-suspending of the induced cultures the bacteria were purified by running the sample through Nickel charged resin. Both the wash buffer and the elution buffer had constant pH of 8. This fits in the pH range in which GFP is stable in being from 6 to 10. (Patterson et al. 1997)
After purification and elution of the GFP containing solution elute was a colorless see-through liquid. It therefore failed to show a presence of GFP that gives elute a bright green color. Furthermore, the SDS gel failed to show a presence of a clear rGFP in the required, 27 kb elution band. There is a faint band that can be noticed, however it could be just an assembly of unrelated proteins or just not sufficient amount of GFP to consider the expression a success.
Discussion: The aim of the experiment was not only to successfully purify the rGFP but also to appreciate its unique properties and to gain the understanding of common techniques used in modern cloning and expression of recombinant proteins, which was successful as it definitely provided an insight into common methods used in biochemical laboratories.
Obtained results showed a partially successful experiment. The plasmid transformation was successful and sufficient bacterial growth on the antibiotic enriched media was observed as shown by Figure 3A. However the expression and purification of the protein did not go according to initial assumptions. There are multiple possibilities, why the experiment did not go as planned. While looking at the SDS-PAGE gel, Figure 3B one can notice that the bands in “pre “and “post” induction samples are exactly the same. As mentioned in the “results “section, low amounts of GFP are expressed even without induction due to promoter polymerase overlapping. Similar band widths in “pre and post” induction wells imply that the inoculation did not happen correct and that possibly the amount of IPTG was not sufficient to induce cells. Moreover the induction took place at inappropriate OD and therefore had to be incubated at 370C overnight. This could result in the ampicillin being used up. E.Coli, being incredibly responsive to its environmental changes ejects the plasmid when theantibiotic is not present in its environment. Potentially the prolonged incubation resulted in the antibiotic being used up and the plasmid being ejected and hence no rGFP production was observed. No production theory is further supported by lack of visibly green, rGFP in the re-suspended pellets. Colleagues who managed to obtain rGFP had a clear, bright green suspension. Suspension obtained by myself was brownish yellowish. At this point it was still unclear whether the experiment was successful since the color only did not forejudge the outcome. Despite lack of visibly green solution, there was a good probability that some amounts of rGFP were produced and will become visible after the purification and will be observed after the SDS-page analysis. The IMAC resulted in completely see-through, clear, colorless elute which further indicated that the experiment has failed. Obtained elute should have been a clear, bright green solution due to the rGFP natural properties, and it was observed as such among colleagues whose experiments were successful. Arguably there is a faint bad present on the SDS-PAGE, however I believe that this is nothing more than contaminants. Since the nickel resin is charged, the band is more than likely to contain various other proteins that are result of a non-specific binding. To examine the purity of a band further and to fully determine whether the obtained band was a purified rGFP it is essential to perform second chromatographic assay, such as size excursion chromatography. At a current time it is impossible to fully determine the nature of obtained band, it could indeed be a low amount of rGFP but most likely it is a contaminant or a degradation product.
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