Two evolutionary distinct translocons import proteins into the apicoplast of toxoplasma gondii
MetadataShow full item record
Apicomplexa are a diverse and medically important group of obligate intracellular parasites. Most apicomplexans harbor a non-photosynthetic plastid (called apicoplast) that was derived by secondary endosymbiosis of a red alga. Despite being tucked away in the dark (unlike the photosynthetic plastids) the apicoplast is home to several biochemical pathways that are essential for parasite growth. Beyond its popularity as the ideal drug target, the interesting evolutionary past of the apicoplast makes it a fascinating model to explore the cell biology of endosymbiosis. In the process of synchronizing its life with the host, majority of the endosymbiont genome was transferred to the host. The nuclear-encoded apicoplast proteome must now be re-routed back to the organelle to perform its function. The mechanisms and molecules that mediate import of such large numbers of cargo proteins across the four membranes surrounding the plastid were largely unknown. It was suspected that the apicoplast might have retained all or parts of the import machinery from the ancestral endosymbiont. The research presented here focuses mainly on endosymbiont derived ERAD and ubiquitination machinery that mediate protein import across periplastid membrane of the apicoplast. By constructing conditional mutants in the Der1Ap and UbcAp genes we show that these proteins are required for import and biogenesis of the organelle and ultimately affect parasite viability. We also provide evidence for presence of additional accessory proteins such as Cdc48Ap, Ufd-1Ap and UbaAp in the peripheral sub-compartment of the organelle. Additionally plant like Tic and Toc translocon components were also identified during the course of this study. Similar genetic interference studies with TgTic20, TgTic22 and TgToc75 show that a highly divergent Tic/Toc machinery mediates protein trafficking through these two innermost membranes of the apicoplast.