Browsing by Subject "purification"

Sort by: Order: Results:

Now showing items 1-5 of 5
  • Taha, Lamia (Helsingin yliopisto, 2021)
    The endoplasmic reticulum (ER) is an important organelle of the cell where a high number of proteins are synthesized and modified to obtain their final structure. Therefore, the ER stress, which is caused by accumulation of unfolded proteins in the ER, is not to be taken lightly since it could contribute to many diseases, such as cancer and neurodegenerative diseases. The response to the ER stress is the unfolded protein response (UPR), which is an adaptive system that helps in adjusting for increased folding needs within the ER. One of the main protein branches in the UPR is inositol requiring enzyme 1 (IRE1). IRE1 detects the status of protein folding inside the ER and initiates the UPR signaling pathway to achieve either normal folding status or cell death. The aim of this research was to express yeast IRE1 in E.coli and human IRE1 in insect cells, purify with affinity chromatography and study the IRE1’s crystal structure with a small molecule modulator that could possibly enhance its activity. The protein was expressed successfully and purified with glutathione S-transferase (GST) tag, and the activity of the pure protein was determined. The structural studies were not fully completed since the absolute purity and yield that was necessary for crystallization was not achieved due to loss of protein during gel filtration and precipitation. Based on the results it is likely that the structure of the protein could be solved and further biochemical and structural studies with F10 are possible.
  • Leden, Laura Irene (2019)
    This case study discusses constraints related to the image of girlhood and gender roles evident in the abridged and adapted Swedish translation of L.M. Montgomery’s girls’ classic Emily of New Moon published in 1955 by C.W.K. Gleerups. The 1950s are called the golden age of girls’ books in Sweden because their publication peaked during this period. However, the popularity of girls’ books during the 1950s did not correlate with high status. Adaptation of translations was common, which indicates the low status of the genre. The Swedish translation of Emily of New Moon was adapted for a younger target audience than Montgomery’s original, and abridged to a lower page count required by the publisher series in which the book was included. The publisher imposed didactic constraints on the book, and these constraints are a sign of conservative and protective strategies and authoritarian attitudes. The adaptation reflects what kind of books the publisher wanted to present to girls, and largely involves purification of unconventional behavior and sexuality. This was consistent with didactic translation norms, reflected in the origin of girls’ books in educational literature. The translation presents a clear, unambiguous and conventional model for the appropriate behavior of girls, and female characters represent more restrictive gender roles than in the original.
  • Lång, Mika (Helsingin yliopisto, 2017)
    Alphaviruses are single-stranded positive-sense RNA viruses that have been the cause of numerous epidemics in the past decades. The viral genome codes four nonstructural proteins that are associated with viral RNA replication. The translation product is a polyprotein from which the individual nonstructural proteins are cleaved. The genome is transcribed by the nonstructural proteins to produce a negative strand, which acts as a template in the synthesis of positive strands. The subgenomic RNA, which codes the structural proteins, is transcribed from the negative template strand. The replication of genomic and subgenomic RNA strands is associated with replication complexes composed of the nonstructural proteins. The replication complexes are housed in membrane invaginations called spherules on the plasma membrane and endolysosomal vesicles. Transfection of plasmids expressing viral replicase proteins and template RNA can also induce formation of replication complexes in addition to live virus infection. Purification of the replication complexes is necessary for detailed functional and structural analysis. In this work, two methods were used in the purification of replication complexes. In the first method, mammalian cells were infected with viruses and replication complexes were blocked on the plasma membrane by drug treatment to prevent transport to endolysosomal vesicles. Cells were lysed and nuclei were removed by centrifugation. The postnuclear supernatant was sedimented by ultracentrifugation in a discontinuous gradient. The gradient was fractionated and the fraction containing the replication complexes was subjected to equilibrium ultracentrifugation to separate particles by density. The fraction containing the replication complexes was studied using electron microscope, and protein and lipid analysis. In the second method, mammalian cells were transfected with plasmids expressing a template RNA and the viral polyprotein to induce formation of replication complexes. A sequence coding hemagglutinin peptide had been inserted into the polyprotein sequence coding for the nonstructural protein with polymerase activity. Cells were lysed and nuclei were removed. Rreplication complexes were immunocaptured using the hemagglutinin tag by subjecting the supernatant to anti-HA agarose beads. Captured replication complexes were eluted with Laemmli sample buffer and purification was examined using Western blotting. Spherules associated with replication complexes were observed using electron microscope and the presence of nonstructural proteins was confirmed with antibodies. Spherules were observed in low numbers and Western blotting revealed that samples contained cellular contaminants. Purification of replication complexes using immunocapture was very low, but more than that of untagged samples. Although significant purification of replication complexes was not achieved, progress was made in the optimization of the methods.
  • Pietila, Maija K.; van Hemert, Martijn J.; Ahola, Tero (2018)
    Positive-strand RNA viruses replicate their genomes in membrane-associated structures; alphaviruses and many other groups induce membrane invaginations called spherules. Here, we established a protocol to purify these membranous replication complexes (RCs) from cells infected with Semliki Forest virus (SFV). We isolated SFV spherules located on the plasma membrane and further purified them using two consecutive density gradients. This revealed that SFV infection strongly modifies cellular membranes. We removed soluble proteins, the Golgi membranes, and most of the mitochondria, but plasma membrane, endoplasmic reticulum (ER), and late endosome markers were retained in the membrane fraction that contained viral RNA synthesizing activity, replicase proteins, and minus-and plus-strand RNA. Electron microscopy revealed that the purified membranes displayed spherule-like structures with a narrow neck. This membrane enrichment was specific to viral replication, as such a distribution of membrane markers was only observed after infection. Besides the plasma membrane, SFV infection remodeled the ER, and the cofractionation of the RC-carrying plasma membrane and ER suggests that SFV recruits ER proteins or membrane to the site of replication. The purified RCs were highly active in synthesizing both genomic and subgenomic RNA. Detergent solubilization destroyed the replication activity, demonstrating that the membrane association of the complex is essential. Most of the newly made RNA was in double-stranded replicative molecules, but the purified complexes also produced single-stranded RNA as well as released newly made RNA. This indicates that the purification established here maintained the functionality of RCs and thus enables further structural and functional studies of active RCs. IMPORTANCE Similar to all positive-strand RNA viruses, the arthropod-borne alpha-viruses induce membranous genome factories, but little is known about the arrangement of viral replicase proteins and the presence of host proteins in these replication complexes. To improve our knowledge of alphavirus RNA-synthesizing complexes, we isolated and purified them from infected mammalian cells. Detection of viral RNA and in vitro replication assays revealed that these complexes are abundant and highly active when located on the plasma membrane. After multiple purification steps, they remain functional in synthesizing and releasing viral RNA. Besides the plasma membrane, markers for the endoplasmic reticulum and late endosomes were enriched with the replication complexes, demonstrating that alphavirus infection modified cellular membranes beyond inducing replication spherules on the plasma membrane. We have developed here a gentle purification method to obtain large quantities of highly active replication complexes, and similar methods can be applied to other positive-strand RNA viruses.
  • Kokkala, Katja (Helsingfors universitet, 2010)
    The characteristics of macrolides are discussed in general level in the theoretical part of this Master's thesis. The discussion is focused on the properties of two macrolides in molecular level and their tendency to form tautomeric forms highlighting the structural similarities and differences of these macrolides, which will affect both the mechanisms of action and the metabolism. Attention is also paid to biosynthesis and manufacturing process keeping focus on downstream process, especially the impurities, which arise from the macrolide biosynthesis. Also the principles of argentation chromatography are discussed. In the experimental part of Master's thesis a purification method for one macrolide was developed using argentation chromatography. Conventional chromatographic purifications cannot separate the macrolide from its impurities. The purity of the macrolide after argentation chromatography was 98.6%. Also a new crystallization method was developed, which produces anhydrous form of the macrolide instead of traditional monohydrate form. A method for analysing the macrolide using HPLC was developed. The method was validated according to ICH guidelines. The tautomeric forms and the impurities of the macrolide were analysed using LC/MS. One of these impurities was isolated and analysed with NMR thus confirming its identity. An analysed NMR spectrum of this impurity has not been published according to our best knowledge. A previously unknown impurity was identified based on MS analysis and retention time.