Knockout of Tyrosine Aminotransferase Gene by Homologous Recombination Arrests Growth and Disrupts Redox Homeostasis in Leishmania Parasite.

Tyrosine aminotransferase is a well-characterized enzyme in the Leishmania parasite, but the role of TAT in the parasite functioning remains largely unknown. In this study, we attempt to gain a better understanding of the enzyme's role in the parasite by gene knockout and overexpression of the TAT gene. The overexpression of TAT protein was well tolerated by the parasites in two independent repeats. Single knockout of TAT gene by homologous recombination, LdTAT+/- displayed distinct retardation in the proliferation rates and entered the death phase immediately. Morphology of LdTAT+/- parasites had important structural defects as they rounded up with elongated flagella. Gene regulation studies suggested the upregulation of key apoptotic and redox metabolism genes in LdTAT+/-. Moreover, LdTAT+/- cells accumulated higher ROS, thiols, intracellular Ca2+ concentrations, and mitochondrial membrane depolarization signifying the onset of apoptosis. Tocopherol levels were reduced by 50% in LdTAT+/- suggesting the involvement of TAT in tocopherol biosynthesis in the parasite. Overall, our results provide the first evidence that gene knockout of TAT results in apoptosis and that TAT is required for the survival and viability of Leishmania donovani.