Development of New Enzyme Activities

UoM administered thesis: Phd

  • Authors:
  • Alexander Wood

Abstract

This thesis reports the exploitation of carboxylic acid reductase adenylation activity to produce a range of primary, secondary and tertiary amides under mild conditions. The amide bond is one of the most vital functionalities in Nature and industry, including the peptide bonds of proteins and the amide linkages of many drug products. However, traditional methods of amide formation suffer from poor atom economy due to the use of coupling agents which must be used in stoichiometric amounts. Meanwhile, the use of organic solvents also worsens the waste and environmental impact of these traditional processes. Biocatalytic methods of amide formation meanwhile, are frequently limited in substrate scope and often also require the use of organic media. A key goal of this PhD project therefore, was the development of new, broad specificity, aqueous enzymatic activities that would produce amides. We initially aimed to produce chimeric enzymes between broad specificity carboxylic acid reductase (CAR) adenylation domains and amide forming nonribosomal peptide synthetase (NRPS) enzyme systems. It was hoped that such a fusion would combine broad specificity carboxylic acid activation with amide forming activity. Ultimately this would prove unsuccessful, yet success would be found by exploiting the broad specificity carboxylic acid activation activity of native CARs directly. This work demonstrates that by altering the reaction conditions of CARs, replacing the natural reducing cofactor NADPH with amine nucleophiles in alkaline conditions, it is possible to intercept activated intermediates to produce amides. Mutational work demonstrated that adenylation activity was sufficient for subsequent amide formation and that the acyl adenylate intermediate could be intercepted to yield amides. Through the introduction of different carboxylic acid substrates and various amines, it was possible to produce a range of primary, secondary and tertiary amides with low conversions. By optimising the reaction conditions, it was possible to produce a target drug molecule, the anticonvulsant ilepcimide, with up to 96% conversion with purified CAR enzyme. Additionally, a scale up reaction using this method with CAR-containing cell lysate allowed the milligram-scale production of ilepcimide with 19% yield. Moreover, ATP consumption assays showed that amide formation and ATP consumption are coupled, suggesting that attack on the acyl adenylate by the amine occurs while the former is still bound to the enzyme. This project, therefore, lays the groundwork for future studies into the extent of amides which can be produced by CARs, and also potentially by the many other adenylating enzymes, with differing and complementary substrate specificities.

Details

Original languageEnglish
Awarding Institution
Supervisors/Advisors
Award date1 Aug 2018