Characterization of TbLpn in Trypanosoma brucei

Abstract

Trypanosoma brucei, is a flagellated, unicellular, parasitic protozoan transmitted by the tsetse fly. It is the source of African sleeping sickness in humans. African sleeping sickness has two different stages, the bloodstream and central nervous system stages, each characterized by different symptoms. Problems with treatment result from severe side effects of the drugs used to treat African sleeping sickness. No vaccine is available due to high antigenic variation. T. brucei exists as two forms. The procyclic fly form relies on oxidative phosphorylation, expresses procyclin as its surface protein, and is morphologically long and slender. In contrast, the mammalian bloodstream form expresses the surface protein VSG, and is characterized as short and stumpy. In T. brucei, gene regulation is controlled primarily at the post-transcriptional level, thus RNA binding proteins play a role in gene regulation. Some RNA binding proteins serve as substrates for enzymes known as protein arginine methyltransferases (PRMTs). These enzymes specifically methylate arginine residues on proteins. A yeast two hybrid approach was used to identify proteins interacting with TbPRMT1 in T. brucei. Among the proteins shown to interact with TbPRMT1, one is a homolog of yeast and mammalian lipin proteins. This protein, which is termed Tblpn, has 2 conserved domains characteristic of lipin proteins. In addition, 2 aspartic acid residues were conserved in T. brucei. Lipin is involved in adipocyte development in mice. A mutation of lipin causes decreased adipocyte development associated with fatty liver dystrophy. Overexpression of the protein results in obesity in mice. Lipin also plays an important role in fatty acid synthesis and signaling in yeast, but possibly relates to the development of important phospholipids in T. brucei, specifically phosphatidylethanolamine and phosphatidylcholine. The objectives of my project were to determine where TbLpn is localized in the cell, to determine whether TbLpn interacts with TbPRMT1 in vivo, and finally to determine if TbLpn is methylated in vivo.