Using peptides to examine the interaction interface between Aspartate transcarbamoylase and Dihydroorotase in pyrimidine biosynthesis in Aquifex aeolicus

Aspartate transcarbamoylase (ATCase) and Dihydroorotase (DHOase) catalyze the second and third steps, respectively, in de novo pyrimidine biosynthesis. Both enzymes form an active complex (DAC) in Aquifex aeolicus, where loop A of DHOase interacts with a domain of ATCase. The main objective of this work is to determine the function of specific residues of loop A in DAC interactions and to alter the catalytic activities through disruption of the interface between the two enzymes from A. aeolicus. The ATCase and DHOase domains have been expressed in Escherichia coli and purified using affinity chromatography. The interface of the published three-dimensional structure of the non-covalently associated dodecamer of DHOase and ATCase from A. aeolicus was examined using bioinformatics, and a peptide was designed to block a specific hydrophobic region. In this work, several peptides have been synthesized by solid phase peptide synthesis (SPPS). Assays were conducted to determine the binding affinities of the peptides to the DHO-ATC complex.