Zebra chip disease is caused by Candidatus Liberibacter solanacearum (Ca. L. solanacearum) and is vectored by the tomato/potato psyllid (TPP). The disease results in the development of blacklines in fried potato tubers which renders them commercially unacceptable. Zebra chip disease has caused significant economic losses to the New Zealand potato industry, thus there
is a need for further understanding of the biology of this unculturable bacterium. The completion of the Ca. L. solanacearum genome in 2011 determined the presence of putative bifunctional genes. Our aim was to determine whether these annotated bifunctional genes were differentially expressed in the vector and host potato plants. Results showed that the purH gene was the most expressed bifunctional gene in TPP and plants whilst the membrane protein, SECDF, was more expressed in plants. The results suggest that these genes could play a role in Ca. L. solanacearum pathogenicity and therefore there is a need to understand the structure and function of the proteins that they encode. The purH gene encodes the bifunctional adenyltransferase-IMP cyclohydrolase protein (ATIC) which catalyses the final two steps of the de novo purine synthesis pathway. The protein was over expressed in E. coli and purified to homogeneity. Attempts to further characterise this protein were undertaken using circular dichroism and differential scanning calorimetry. The research presents an opportunity to understand potential changes that could occur in protein structure and function in a reduced genome organism.