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Title: Recombinant transketolases with increased synthetic potential
Author: Bacon, Sarah Louise
ISNI:       0000 0001 3435 0015
Awarding Body: University of London
Current Institution: University College London (University of London)
Date of Award: 2003
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This thesis describes the progress made towards the development of recombinant enzymes for use in the catalysis of a carbon-carbon bond-forming reaction. Transketolase (TK) is one such enzyme and has considerable synthetic potential as a stereospecific C-C bond-forming reagent. Recombinant forms of TK from Escherichia coli have been produced, over-expressing to levels of 15-25% of the total cellular protein. The native enzyme is stereospecific for D-enantiomeric, linear sugar aldehyde acceptors. It also dictates the stereochemistry of the two new chiral centres in the reaction product. Furthermore, it has been shown to have activity with a range of simple α-unsubstituted aldehydes, so demonstrating a low specificity for the aldehyde component. Combined with the high stereoselectivity for the C-C bond-forming step, this makes TK an attractive catalyst for asymmetric synthesis. Using the enzyme crystal structure as a model for their design, a selection of TK mutants were generated with assorted combinations of amino acid changes located within the active site funnel. The synthetic potential of these modified TKs was analysed combinatorially with a range of aromatic aldehydes, using β-hydroxypyruvic acid as the ketol donor. Relaxation or reversal of the TK requirement for a D- α-hydroxyl group would provide even greater scope for its syntheic applications. Variants tailored for these needs were constructed and characterised using D-glyceraldehyde and DL-glyceraldehyde as aldehyde acceptors. In addition, an ion-exchange chromatographic method of purification was developed for a poly-lysine tagged version of TK, affording a 4.5-fold purification of the enzyme. The TK thus produced is available for subsequent investigations into its specific reactivity with a range of substrates.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available