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| 2. |
- Abahazi, Emese, et al.
(författare)
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Covalently immobilized Trp60Cys mutant of omega‰-transaminase from Chromobacterium violaceum for kinetic resolution of racemic amines in batch and continuous-flow modes
- 2018
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Ingår i: Biochemical engineering journal. - : Elsevier. - 1369-703X .- 1873-295X. ; 132, s. 270-278
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Tidskriftsartikel (refereegranskat)abstract
- Covalent immobilization of an engineered omega-transaminase mutant Trp60Cys from Chromobacterium violaceum (CvTAW60C) was performed on bisepoxide-activated aminoalkyl resins. Activity of the various CvTAW60C preparations was evaluated in kinetic resolution of four racemic amines (rac-1a–d). The most active EA-G-CvTAW60C preparation (CvTAW60C attached to polymeric resin with ethylamine function activated with glycerol diglycidyl ether—EA-G) could perform the kinetic resolution of racemic 4-phenylbutan-2-amine (rac-1a) over 49% conversion up to 19 consecutive reaction cycles or in media containing up to 50% v/v DMSO as cosolvent in batch mode reactions. The immobilization process of CvTAW60C onto the EA-G resin filled in stainless steel bioreactors was also tested in flow-through mode. Kinetic resolution of three racemic amines containing aromatic moieties (rac-1a-c) was performed in continuous-flow mode resulting in easy-to-separate mixture of the corresponding ketone (2a–c) and the non-converted (R)-amine in high enantiopurity (ee(R)-1a-c ≥ 96%).
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| 3. |
- Spadiut, Oliver, et al.
(författare)
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Improving thermostability and catalytic activity of pyranose 2-oxidase from Trametes multicolor by rational and semi-rational design
- 2009
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Ingår i: The FEBS Journal. - : Wiley. - 1742-464X .- 1742-4658. ; 276:3, s. 776-792
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Tidskriftsartikel (refereegranskat)abstract
- The fungal homotetrameric flavoprotein pyranose 2-oxidase (P2Ox; EC 1.1.3.10) catalyses the oxidation of various sugars at position C2, while, concomitantly, electrons are transferred to oxygen as well as to alternative electron acceptors (e.g. oxidized ferrocenes). These properties make P2Ox an interesting enzyme for various biotechnological applications. Random mutagenesis has previously been used to identify variant E542K, which shows increased thermostability. In the present study, we selected position Leu537 for saturation mutagenesis, and identified variants L537G and L537W, which are characterized by a higher stability and improved catalytic properties. We report detailed studies on both thermodynamic and kinetic stability, as well as the kinetic properties of the mutational variants E542K, E542R, L537G and L537W, and the respective double mutants (L537G/E542K, L537G/E542R, L537W/E542K and L537W/E542R). The selected substitutions at positions Leu537 and Glu542 increase the melting temperature by approximately 10 and 14 degrees C, respectively, relative to the wild-type enzyme. Although both wild-type and single mutants showed first-order inactivation kinetics, thermal unfolding and inactivation was more complex for the double mutants, showing two distinct phases, as revealed by microcalorimetry and CD spectroscopy. Structural information on the variants does not provide a definitive answer with respect to the stabilizing effects or the alteration of the unfolding process. Distinct differences, however, are observed for the P2Ox Leu537 variants at the interfaces between the subunits, which results in tighter association.
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| 4. |
- Vertessy, Beata G, et al.
(författare)
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Specific Derivatization of the Active Site Tyrosine in dUTPase Perturbs Ligand Binding to the Active Site
- 1996
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Ingår i: Biochemical and Biophysical Research Communications. - : Elsevier BV. - 1090-2104 .- 0006-291X. ; 219:2, s. 294-300
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Tidskriftsartikel (refereegranskat)abstract
- Selective modification of one (of three) tyrosine residue per enzyme monomer leads to inactivation of dUTPase of the retrovirus equine infectious anemia virus (EIAV). The substrate dUMP and the cofactor Mg2+protects against inactivation and modification, in agreement with the study onE. colidUTPase (Vertessyet al.(1994)Biochim. Biophys. Acta1205, 146-150). Amino acid analyses of nitrated dUTPases confirmed Tyr-selectivity of modification. The nitrated residue inE. colidUTPase was identified as the evolutionary highly conserved Tyr-93. The modifiable residue is shown to be the only Tyr exposed in bothE. coliand EIAV dUTPases. As a consequence of Tyr-93 derivatization, the Mg2+-dependent interaction between the substrate-analogue dUDP andE. colidUTPase becomes impaired as shown by circular dichroism spectroscopy, here presented as a tool for monitoring ligand binding to the active site.
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| 5. |
- Vertessy, Beata G., et al.
(författare)
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The complete triphosphate moiety of non-hydrolyzable substrate analogues is required for a conformational shift of the flexible C-terminus in E. coli dUTP pyrophosphatase
- 1998
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Ingår i: FEBS Letters. - 1873-3468. ; 421:1, s. 83-88
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Tidskriftsartikel (refereegranskat)abstract
- The molecular mechanism of substrate analogue interaction with Escherichia coli dUTPase was investigated, using the non-hydrolyzable 2'-deoxyuridine 5'-(α,β-imido)triphosphate (α,β-imido-dUTP). Binding of this analogue induces a difference in the far UV circular dichroism (CD) spectrum arguing for a significant change in protein conformation. The spectral shift is strictly Mg2+-dependent, does not appear with dUDP instead of α,β-imido-dUTP and is not elicited if the flexible C-terminal arm is deleted from the protein by limited tryptic digestion. Involvement of the C-terminal arm in α,β-imido-dUTP binding is consistent with the finding that this analogue protects against tryptic hydrolysis at Arg-141. Near UV CD of ligand-enzyme complexes reveals a characteristic difference in the microenvironments of enzyme-bound dUDP and α,β-imido-dUTP, a difference not observable in C-terminally truncated dUTPase. The results suggest that (i) closing of the active site during the catalytic cycle, through the movement of the C-terminal arm, requires the presence of the complete triphosphate moiety of the substrate in complex with Mg2+, and (ii) after catalytic cleavage the active site pops open to facilitate product release.
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