Visceral Leishmaniasis is an important public health threat in parts of India. It is caused by a protozoan parasite, Leishmania donovani. Currently, available drugs manifest severe side effects. Hence, there is a need to identify new drug targets and drugs. Aminoacyl-tRNA synthetases required for protein synthesis are known drug targets for bacterial and fungal pathogens. The aim of the present study was to obtain essentiality data for Leishmania donovani leucyl-tRNA synthetase (LdLRS) by gene replacement. Gene replacement studies indicate that this enzyme plays an essential role in the viability of this pathogenic organism and appears to be indispensable for its survival in vitro. The heterozygous mutant parasites demonstrated a growth deficit and reduced infectivity in mouse macrophages as compared to the wild type cells. We also report that Leishmania donovani recombinant LRS displayed aminoacylation activity and the protein localized to both the cytosol and mitochondrion. A broad-spectrum antifungal 5-fluro-1,3-dihydro-1-hydroxy-2,1-benzoxaborole (AN2690) was found to inhibit parasite growth in both the promastigote and amastigote stages in vitro as well as in vivo in BALB/c mice. This compound exhibited low toxicity to mammalian cells. AN2690 was effective in inhibiting the aminoacylation activity of the recombinant LdLRS. We provide preliminary chemical validation of LdLRS as a drug target by showing that AN2690 is an inhibitor both of L. donovani LRS and of L. donovani cell growth.
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