The development of biocatalytic methods for the production of CoA analogues
Thesis (MSc (Chemistry and Polymer Science))--University of Stellenbosch, 2006.
This work focuses on the biocatalytic production of coenzyme A (CoA) analogues with different tether lengths in its pantetheine moiety, and on analogues where the cysteamine moiety has been replaced with a range of other amines. An attempt was made to develop a simple biocatalytic method for the optimum production of such CoA analogues by chemo-enzymatic means. Pantothenic acid ethyl thioesters with different tether lengths were first synthesized as substrates of the CoA biosynthetic enzymes, CoaA, CoaD and CoaE. The acceptability of these compounds as substrates for the pantothenate kinase (CoaA) from prokaryotic and eukaryotic organisms was investigated through kinetic studies. These substrates were subsequently exposed to CoaA, CoaD and CoaE to produce various general CoA synthons (ethyl pre-CoAs). Finally aminolysis of these ethyl pre-CoAs by cysteamine and homocysteamine gave the various CoA analogues of different tether lengths in their pantetheine moiety. The identical production of a second type of CoA synthon (phenyl pre-CoA) from pantothenic acid phenyl thioesters was also investigated as a means to increase reactivity of the thioester substrates. Aminolysis of the phenyl pre-CoA produced the corresponding CoA derivative, but reactivity was lower than expected. A second strategy was also developed where the pantothenic acid phenyl thioesters were first aminolyzed, resulting in various pantothenamide intermediates. Aminolysis was attempted with thiol-bearing amines such as cysteamine and homocysteamine as well as with amines without sulfhydryl functionalities. These pantothenamide intermediates were then used in the biosynthesis of the corresponding CoA analogues by addition of CoaA, CoaD and CoaE. The ideal method of CoA analogue production will utilize a continuous bioreactor system in which these analogues can be prepared on large scale. However, to construct a bioreactor the enzymes involved need to be immobilized on a matrix in order to transform substrate to product. The enzymes CoaA, CoaD and CoaE can be immobilized on cellulose via a cellulose binding domain (CBD) affinity tag. Various types of CBDs were investigated and used in the construction of suitable expression vectors. Optimum expression conditions to obtain soluble CBD-fused enzymes were developed.