Der Nachweis eines Mitglieds der OMP85-Proteinfamilie im Apikoplasten von Toxoplasma gondii

As with many members of the Chromalveolates, the intracellular parasite Toxoplasma gondii harbors a plastid which is called the apicoplast. This kind of plastid has been evolved by secondary endosymbiosis, an event in which a rhodophyte was engulfed by another eukaryotic cell. During the course of evolution, the endoysmbiont became established as an organelle. Due to the horizontal gene transfer between the host nucleus and the secondary plastid most of the apicoplast proteins are encoded in the host nucleus, synthesized in the ER and therefore must be reimported into the plastid. Since the apicoplast features four membranes, proteins destined for the plastid stroma have to traverse them by using a protein import machinery. Even though some components of this machinery, SELMA in the PPM and a Tic20-homologue in the innermost apicoplast membrane, have been identified, the details of the import mechanism are still unknown. Based upon bioinformatic analyses, two proteins of the OMP85-family were identified in the genome of T. gondii. Depending on their function proteins of this family can be devided further into two subgroups. Proteins of Toc75-subtype are involved in protein transport whereas members of Sam50-subtype are characterized as components of protein insertion and assembly machineries. During the course of this work one protein of the OMP85-family (TgOMP85) could be localized in the apicoplast of the parasite. After a verification of the gene model TgOMP85 can definitely be assigned to the OMP85-family. Furthermore like most of the apicoplast proteins it possesses a functional BTS-sequence at its N-terminus, which is responsible for targeting the protein to the plastid. In order to verify if TgOMP85 respresents a component of the protein import machinery in the third apicoplast membrane, further analysis has to be carried out. The second identified protein in the apicomplexan parasite was localized in the mitochondrium and is designated as TgSam50. Due to its gene sequence and its localization this protein can be assigned to the Sam50-subtype of the OMP85-family. Whether TgSam50 is in fact involved in the integration events of proteins into the outer mitochondrial membrane remains to be clarified.