A Key Enzyme Behind the Bug?: Characterization of Candidatus phytoplasma AYWB Malic Enzyme

SAIGO, MARIANA; MUSSI, MARÍA ALEJANDRA; ALVAREZ, CLARISA; MACLEAN, ALLYSON; ANDREO, CARLOS; HOGENHOUT, SASKIA; DRINCOVICH, MARÍA FABIANA

Puerto Varas

Congreso; SAIB. XLIX Reunión Anual; 2013

Sociedad Argentina de Investigaciones en Bioquímica y Biología Molecular

Phytoplasmas are insect-vectored plant pathogens that infect a range of high-value agricultural crops. They are obligate parasites that survive and replicate intracellularly within both insect and plant hosts. As a consequence of genome reduction, their metabolic capabilities are hardly impaired, resulting in a strict nutrient dependence on their hosts which negatively affects the proper development of the plant. It is not clear what is the preferred carbon source, as sugars do not seem to be the best option according to the metabolic pathways deduced from genome analysis. However, a pathway for malate conversion to acetate appears an appropriate alternative. In this work, we expressed and purified the recombinant putative malic enzyme encoded in Ca. P. asteris strain AYWB, and performed kinetics and structural studies, as well as analyzed its phylogenetic relatedness. Our studies show that the enzyme is active with both cofactors NAD and NADP, showing maximum activity at pH 8.2, and following a steady-state random mechanism (Bi-Ter kinetics). Besides, we have observed modulation by metabolites abundant in the phloem such as glutamine and glutamate. Most interestingly, the enzyme is activated by ADP while inhibited by ATP, giving a strong indication of the involvement of the enzyme in the bacterial energetic metabolism. Finally, phylogenetic analyses show that the enzyme follows the species evolution, and that it has not been acquired by horizontal gene transfer events. Overall, our results provide evidence on the functionality and kinetic properties of this enzyme which could play a key role in phytoplasma pathogenesis.