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Molecular dynamics simulations of complexes consisting of proteins and nucleic acids
Hammer, Jiří ; Barvík, Ivan (advisor) ; Obšil, Tomáš (referee)
The goal of this diploma thesis was to study interactions of Argonaute (Ago) protein in a complex with nucleic acids. Based on the available crystal structures of full length Argonaute (from A. aeolicus, Aa-Ago) and/or its domains (human PAZ domain, Hs-PAZ), twelve different simulations were computed. Two initial simulations used model of Aa-Ago with either a duplex of DNA/RNA or RNA/RNA. Major difference was in behavior of the PAZ domain (especially its arginine residues), which tolerated the guide DNA in one simulation, but was disturbing the RNA guide strand in the second. Such an interaction could serve as a mechanism of the substrate recognition. In additional simulations (3-9) employing the Hs-PAZ domain, where no disturbance was found in the DNA/RNA hetero-duplex. Different arrangements of the active site geometry as well as empirical parameterizations of Mg2+ ion were probed and analyzed. The DD-catalytic motif plus D683 in Aa-Ago (equivalent to H807 in human Argonaute2) was observed to coordinate the Mg2+ ion in one and two metal ion dependent catalysis models. Highly conserved R570 and E578 created mutual hydrogen bonds and hence stabilized the active site. To make the cleavage irreversible, a role for the first (unpaired) nucleotide from 5'-end of the guide strand was suggested. It lies in a...
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Inhibition of Thymidine Phosphorylase
Zákoucká, Eva ; Brynda, Jiří (advisor) ; Obšil, Tomáš (referee)
2. Abstract Thymidine phosphorylase (TPase), also known as gliostatin or Platelet-derived endothelial cell growth factor (PD-ECGF), is an enzyme with an important role in the nucleoside metabolism and is also involved in degradation and recycling of DNA. TPase catalyzes the reversible phosphorolysis of pyrimidine 2'-deoxynucleosides to 2-deoxy-D-ribose-1- phosphate and their respective bases, as well as the transfer of the deoxyribosyl moiety from one pyrimidine base to another. Thymidine phosphorylase is a therapeutic target of great importance because of its participation in angiogenesis especially in solid tumors of various tissues. Therefore, TPase stimulates tumor growth and progression, as well as metastasis. In addition to this, TPase inhibits apoptosis, particularly of tumor cells and causes degradation of several antiviral and anticancer drugs. Apart from the carcinoma tissues, thymidine phosphorylase is overexpressed in various other tissues affected by disorders characterized by proliferation of blood vessels including psoriasis, rheumatoid arthritis and atherosclerosis. Inhibiting the activity of TPase selectively in the tissues affected by the diseases listed above would be of great therapeutic significance. Therefore, many inhibitors, mainly substrate analogues, have been designed based on the...
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Study of structural differences among 14-3-3 protein isoforms.
Macáková, Eva ; Gryčová, Lenka (referee) ; Obšil, Tomáš (advisor)
The 14-3-3 proteins are a family of important regulatory proteins, found in all eukaryotes, which are involved in many cellular processes. In this diploma thesis, we studied structure/function relationships of 14-3-3 proteins, in this case it was the influence of the structure of H8-H9 loop on the binding affinity in barley isoform hv 14-3-3A and human isoform 14-3-3ζ. According to former results, hv 14-3-3A binds to a ligand with lowest affinity, which could be caused by present of a glycin in H8-H9 loop, while in other isoforms there is a serin on the same position. We measured the binding affinity in protein hv 14-3-3A WT and its mutant, which contained the serin instead of the glycin in H8-H9 loop. For comparison, we also measured the binding affinity of human isoform 14-3-3ζ containing the serin in H8-H9 loop and its mutant, where the the serin was replaced by the glycin. Proteins were expressed in E. coli cells strain BL21(DE3) and then purified. The dissociation constant for the binding of peptide pRaf-259 labeled with fluorophores FITC and ATTO was measured using both the fluorescence correlated spectroscopy and the steady-state fluorescence intensity. Our results showed that in both isoforms the mutation of H8-H9 loop causes decrease in the binding affinity.
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Study of the interaction between the C-terminus of DNA-binding domain of FOXO4 and DNA
Zusková, Iva ; Teisinger, Jan (referee) ; Obšil, Tomáš (advisor)
Forkhead transcription factors are structurally similar molecules containing approximately 110-amino-acid-long DNA-binding domain known as a forkhead domain. Protein FOXO4 is a member of subgroup "O" of forkhead transcription factors. Members of this subgroup play a key role in many biologically important processes. For example, FOXO factors participate in metabolism control, cell-cycle control, apoptosis and oxidative stress resistance. The forkhead domain (DNA-binding domain) consists of three α-helices (H1, H2 and H3), three β-strands (S1, S2 and S3) and two flexible loops (called wings W1 and W2). The role of the wing W2 in FOXO binding to the target DNA is still elusive. Wing W2 probably interacts with the DNA in the region upstream of the core motif. It has been speculated that the FOXO DNA-binding affinity depends on A-T content (number of A-T pairs) in the region upstream of the core motif. In order to investigate this hypothesis, DNA- binding domain of the FOXO4 protein was expressed and purified and it was determined its binding affinity for three molecules of double stranded DNA containing different number of A-T pairs in the region upstream of the core motif using steady-state fluorescence anisotropy- based method. Our results show no significant differences between obtained FOXO4...
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