Functional characterization of the first lipoyl-relay pathway from a parasitic protozoan

Lipoic acid (LA) is a sulfur-containing cofactor covalently attached to key enzymes of central metabolism in prokaryotes and eukaryotes. LA can be acquired by scavenging, mediated by a lipoate ligase, or de novo synthesized by a pathway requiring an octanoyltransferase and a lipoate synthase. A more complex pathway, referred to as “lipoyl-relay”, requires two additional proteins, GcvH, the glycine cleavage system H subunit, and an amidotransferase. This route was described so far in Bacillus subtilis and related Gram-positive bacteria, Saccharomyces cerevisiae, Homo sapiens, and Caenorhabditis elegans. Using collections of S. cerevisiae and B. subtilis mutants, defective in LA metabolism, we gathered evidence that allows us to propose for the first time that lipoyl-relay pathways are also present in parasitic protozoa. By a reverse genetic approach, we assigned octanoyltransferase and amidotransferase activity to the products of Tb927.11.9390 (TblipT) and Tb927.8.630 (TblipL) genes of Trypanosoma brucei, respectively. The B. subtilis model allowed us to identify the parasite amidotransferase as the target of lipoate analogs like 8-bromo-octanoic acid, explaining the complete loss of protein lipoylation and growth impairment caused by this compound in T. cruzi. This model could be instrumental for the screening of selective and more efficient chemotherapies against trypanosomiases.M.C.M and A.D.U. are members of the Carrera del Investigador Científico del Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET), Argentina. A.S. is a doctoral fellow from CONICET, A.L and D.A.L were doctoral fellows and P.V. was a career member from the same institution. This work was supported by Fondo para la Investigación Científica y Tecnológica (Grant PICT 2016-1853); Ministerio de Ciencia Tecnología e Innovación Productiva (Grant EULACH 16/T02-0161); and Consejo Nacional de Investigaciones Científicas y Técnicas (Grant P-UE-0039 2016).Peer reviewe