Trypanosoma cruzi would not be able to scavenging lipoic acid

LAMBRUSCHI D.; UTTARO, ANTONIO D.

Rosario

Congreso; XXVII Reunión anual de la SAP; 2013

Lipoic acid (LA) is a cofactor of 2-oxoacid dehydrogenases (2OADH) and glycine cleavage (GCC) complexes. As these enzymatic complexes are essential to the cell, LA biosynthesis and lipoilation mechanisms are potential chemotherapeutic targets against parasites like Trypanosoma cruzi and T. brucei. Many organisms have LA salvage pathways by which they scavenge free LA from their environment and lipoilate proteins using lipoate:protein ligase enzymes. The LA analog 8-bromo-octanoate is a ligase inhibitor which produces strong growth inhibition of Escherichia coli and ?of particular relevance- the protozoan parasite Plasmodium falciparum. We found ligase orthologs in the trypanosomatid´s genome but, notably, 8-bromo-octanoate did not show any deleterious effect against T. cruzi epimastigotes. These results could be explained if despite encoding a true lipoate:protein ligase, the trypanosome ortholog is involved in the transference of the octanoyl moiety from the GCC H subutit to the E2 subutit of dehydrogenases, such as in Bacillus subtilis and Saccharomcyces cerevisiae, acting as amidotransferase, to which they share significant protein similarity. Another possibility is that trypanosomes are unable to take up 8-bromo-octanoate. We assessed this hypothesis in an indirect way, assuming the drug is imported by the same mechanism that octanoate and, probably, lipoate. Isotopic cell-labeling assays using [14C]-octanoate, a lipoate biosynthesis precursor, did not result in labeled lipoylated or octanoylated proteins. In addition, transport assays showed a negligible uptake of [14C]-octanoate by intact T. cruzi epimastigote cells, one order of magnitude lower than the level of [14C]-palmitate uptake. Taken together, these results suggest that T. cruzi would not be able to take up octanoate nor 8-bromo-octanoate from the media, in agreement with the lack of a LA salvage mechanism, paralleling the lack of a true lipoate:protein ligase, as found in yeasts.