One of the hallmarks of eukaryotic cells is the ability to form barriers through the formation of a lipid membrane bilayer. This process of compartmentalization ensures that cells can establish various distinct intracellular environments, which at the cellular level can be the basis for higher order functions. One such example, the secretory pathway, is a network of vesicular compartments that contain or transport a specific repertoire of proteins. In the early secretory pathway, coated protein complex II (COPII)-coated vesicles mediate the anterograde transport of newly synthesized secretory cargo from the endoplasmic reticulum (ER) to the Golgi apparatus. The COPII complex is comprised of five proteins (Sar1, Sec23, Sec24, Sec13, and Sec31) that are sequentially recruited to ER exit sites (ERES) upon the activation of Sar1, a small GTPase. This leads to deformation of the ER membrane and the formation of a transport vesicle. Simultaneously, the COPII complex is responsible for capturing and incorporating cargo proteins into the budding vesicle. By controlling this initial stage of the secretory pathway, COPII selectivity for various cargo proteins acts to mediate forward trafficking.

The current project is to further elucidate the molecular factors that dictate the selectivity of COPII vesicles, especially with regard to glycosylphosphatidylinositol (GPI)-anchored proteins, in African trypanosomes. GPI-anchored proteins are ubiquitous among eukaryotes, and their study in trypanosomes has paved the way for many scientific discoveries in eukaryotic cell biology. While a clinically relevant human and veterinary parasite, Trypanosoma brucei also provides a unique model organism for the current Aims of this research project. Having a digenetic life cycle, T. brucei has both a mammalian and an insect vector (tsetse fly) stage with distinct environmental adaptations. The specific Aims are designed to investigate the COPII subunits that mediate the trafficking of GPI-anchored cargo and determine COPII selectivity at both stages of the parasite’s life cycles. Also, to determine if the COPII subunits assemble into homotypic or heterotypic vesicles.