Submitted to: Molecular and Biochemical Parasitology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/18/2011
Publication Date: 2/1/2012
Publication URL: http://handle.nal.usda.gov/10113/56603
Citation: Caballero, M.C., Pedroni, M.J., Palmer, G.H., Suarez, C.E., Davitt, C., Lau, A.T. 2012. Characterization of acyl carrier protein and LytB in Babesia bovis apicoplast. Molecular and Biochemical Parasitology. (2):125-33. Interpretive Summary: The apicoplast is a highly specialized organelle that mediates required functions in the growth and replication of apicomplexan parasites.In this study we used four linked approaches to identify and characterize apicoplast-related key pathways in B. bovis: i) structural characterization of the apicoplast in the asexual stage of the parasite; ii) identification of the type II fatty acid biosynthesis (FASII) and non-mevalonate 1-deoxy-D-xylulose-5-phosphate (DOXP) isoprenoid (MEP) biosynthesis using ACP and LytB as markers; iii) testing the role of the bipartite targeting signals in trafficking to the apicoplast lumen; and iv) testing the sensitivity of the FASII and MEP pathways to specific pharmacologic inhibition. Results from our pharmacological inhibitions, however, suggest that while B. bovis may have MEP pathway as do some apicomplexans, FASII may not be present which raises the question of the true function, if any, of ACP in Babesia.
Technical Abstract: The apicoplast is a highly specialized organelle that mediates required functions in the growth and replication of apicomplexan parasites. Despite structural conservation of the apicoplast among different parasite genera and species, there are also critical differences in the metabolic requirements of different parasites and at different stages of the life cycle. To specifically compare apicoplast pathways between parasites that have both common and unique stages, we characterized the apicoplast in Babesia bovis, which has only intraerythrocytic asexual stages in the mammalian host, and compared it to that of Plasmodium falciparum, which has both asexual intraerythrocytic and hepatic stages. Specifically focusing on the type II fatty acid (FASII) and isoprenoid (MEP) biosynthesis pathways, we searched for pathway components and retention of active sites within the genome, localized key components [acyl carrier protein (ACP) and 4-hydroxy-3-methylbut-2-enyl diphosphate reductase (LytB)] to the apicoplast, and demonstrated that the N-terminal bipartite signals of both proteins are required and sufficient for trafficking to the apicoplast lumen. Using specific pharmacologic inhibition, we demonstrated that MEP biosynthesis may be disrupted and its presence is required for intraerythrocytic growth of B. bovis asexual stages, consistent with the genomic pathway analysis and with its requirement in the asexual erythrocytic stages of P. falciparum. In contrast, FASII biosynthesis may or may not be present and specific drug targets did not have any inhibitory effect to B. bovis intraerythrocytic growth, which is consistent with the lack of requirement for P. falciparum intraerythrocytic growth. However, genomic analysis revealed the loss of FASII pathway components in B. bovis whereas the pathway is intact for P. falciparum but regulated to be expressed when needed (hepatic stages) and silent when not (intraerythrocytic stages). The results indicate specialized molding of apicoplast biosynthetic pathways to meet the requirements of individual apicomplexan parasites and their unique intracellular niches.