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Enzymatic detoxification of cyanide using cyanide hydratases
Sedova, Anastasia ; Rucká, Lenka ; Glozlová, Michaela ; Novotný, Petr ; Martínková, Ludmila ; Bojarová, Pavla
Cyanide, a strong chelator of metals in vital enzymes and proteins, is very toxic for most living organisms. Wastewaters from the mining, metallurgical and chemical industries contain significant concentrations of free cyanide. Though it can be largely eliminated by physicochemical methods, these processes may in turn lead to the formation of other waste. In addition, no effective methods have been found to neutralize cyanide spills coming from industrial accidents. The use of enzymes to remove cyanide is an attractive alternative, which is environmentally friendly and applicable to high cyanide concentrations. Cyanide hydratases (CynHs) are of considerable interest for the decomposition of hazardous cyanide wastes. Here we investigate the biochemical properties of new CynHs from Stereum hirsutum and Exidia glandulosa, it is of fundamental importance to preserve the enzyme activity at alkaline pH as cyanide waste is stored under these conditions.
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Engineering of microbial glycosidases for modifying synthetic potential
Hovorková, Michaela ; Bojarová, Pavla (advisor) ; Lichá, Irena (referee)
Glycosidases (EC 3.2.1.) alias glycoside hydrolases are enzymes that catalyze the cleavage of a glycosidic bond between two carbohydrates or between a carbohydrate and an aglycone. Under suitable conditions (especially reduction of water activity in the reaction mixture), these enzymes are also able to synthesize a glycosidic bond. By targeted mutagenesis of the catalytic centre of the enzymes, it is possible to suppress or completely abolish their hydrolytic activity. Enzyme synthesis using glycosidases makes it possible to prepare bioactive galactosides, for example galectin ligands. The present work deals mainly with β-galactosidase from Bacillus circulans, its recombinant expression and mutagenesis. In the first part of the work, the commercially prepared plasmid of -galactosidase from B. circulans isoform A that I designed was used for recombinant expression in E. coli. It was necessary to optimize the conditions of the enzyme production. As it is a large protein (189 kDa), the expression vector pCOLD II and cold production at 15 ř C were used. The enzyme is specific for the formation of the β-1,4 glycosidic bond and has been used to synthesize complex tri- and tetrasaccharide ligands that cannot be prepared with a crude commercial preparation containing undesirable enzyme activities....
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Mutant glycosidases with a high substrate specificity and their analysis
Nekvasilová, Pavlína ; Bojarová, Pavla (advisor) ; Lichá, Irena (referee)
β-N-acetylhexosaminidases (EC 3.2.1.52, GH 20) are retaining exo-glycosidases that in vivo cleavage both β-N-acetylglucosamine (GlcNAc) or β-N-acetylgalactosamine (GalNAc) residues fom glycostructures. Under suitable reaction conditions, these enzymes are able to synthesize the glycosidic bond in good yields. Substitution of selected amino acid(s) in the emzyme active site by site-directed mutagenesis may change the enzyme's substrate specificity or suppress the hydrolytic activity of the enzyme in favor of synthesis. The present thesis deals with three mutant β-N-acetylhexosaminidases from Talaromyces flavus, in which the amino acid residues responsible for binding to C-4 hydroxyl of the substrate (Arg218, Glu546) were exchanged for amino acids proposed on the basis of molecular modeling. The effect of introduced single point mutations on substrate specificity of prepared enzymes was studied. Mutant β-N-acetylhexosaminidases were heterologously expressed in Pichia pastoris and characterized. Furthermore, transglycosylation reactions with these enzymes were performed. The prepared carbohydrate products were characterized by NMR.
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Modified Substrates in β-N-Acetylhexosaminidase-Catalyzed Synthesis
Bojarová, Pavla ; Křen, Vladimír (advisor) ; Moravcová, Jitka (referee) ; Walterová, Daniela (referee)
4 Conclrrsion 4 CoNcrusroN This Ph. D. thesis is a systematic study of the substrate specificity and the synthetic potential of B-N-acetylhexosaminidases (EC 3.2.1.52) with structurally modified substrates. It comprises four publications in intemational journals, one review and 17 oral and poster contributions. The following parts of the substrate molecule were modified: 2-acetamido moiety, the C-6 hydroxyl (oxidations, introduction of a cyano group) and the aglycon part (glycosyl azides - C-N bond hydrolysis). Thirteen modified substrates were synthesized, seven of them were described for the first time. They were tested for hydrolysis and transglycosylation by over thirty fungal $-N-acetylhexosaminidases (culture collections at Charles University and at the Institute of Microbiology, Academy of Sciences of the Czech Republic) and the results were discussed in relation to the conclusions of molecular modeling (B-N-acetylhexosaminidase from Aspergillus oryzae CCF 1066). Eight oligosaccharidic structures (six of them novel) were prepared by semi- preparative transglycosylation reactions (tens of miligrams), isolated (mostly 16_377a yields, even 787o yie\ď) and fully characterized. Noteworthy properties like immunoactivity (binding to natural killer cell activation receptors) and inhibitory potential were...
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