Unique and conserved features of the protein synthesis apparatus in parasitic trypanosomatid (trypanosoma and leishmania) species

Abstract

Trypanosomatids are flagellated protozoans that diverged very early on from the lineages leading to the other eukaryotic groups with the consequence that they have evolved separately for ˜1 billion years. Pathogenic trypanosomatids, belonging mainly to Trypanosoma and Leishmania species, have been intensively studied, and there is a degree of understanding regarding their genome structure, mRNA synthesis and translation. A compilation of our knowledge of trypanosomatid protein synthesis is described here. Homologs of most known translation factors characterized in yeast, animals and plants have been clearly identified consistent with the presence of the core translation machinery in the last eukaryotic common ancestor. Further, lack of identification of a few absent factors may be more a consequence of too much divergence in sequences than due to a real absence. However, there has been an elaboration of function in trypanosomatids including: (1) an expansion in the number of homologs of eIF4F subunits, leading to several novel eIF4F-like complexes; (2) changes in cytoplasmic ribosome structure and in its rRNA scaffold; (3) novel mechanisms of mitochondrial tRNA import; (4) a unique mitochondrial ribosome; (5) a great number of hypothetical RNA-binding proteins of unknown function. Overall, and perhaps due to the post-transcriptional nature of the gene expression control in trypanosomatids, they consistently display novel mechanisms and features that deserve better attention and may clarify aspects of the eukaryotic protein synthesis apparatus in general.