Evolutionarily Diverged TRAPP Components in Giardia lamblia That Lacks a Classical Golgi.

The endomembrane system of the intestinal pathogen Giardia lamblia lacks a separate Golgi compartment. Without this sorting compartment, how cargo sorting to various subcellular destinations occurs within Giardia remains an open question. While the distribution of various Golgi-associated SNAREs and Rabs has been documented in this parasite, the TRAPP (TRAnsport Protein Particle) complex, a guanine nucleotide exchange factor for Golgi-associated Rabs, remained uncharacterized. Herein, we report that Giardia expresses a minimal set of TRAPP complex components, GlBet3, GlBet5, GlTrs23, and GlTrs31. Some of these components can interact with GlRab1a, GlRab11, and the COPII coat protein, GlSec23. Coupled with the colocalization and coimmunoprecipitation of GlBet3 and GlBet5, we propose the existence of a functional TRAPP complex in Giardia with an architecture that is different from that of yeast. While some interactions within this complex may be analogous to those in yeast, we find evidence of some unique interactions as well. The TRAPP genes are upregulated during encystation, and two components are associated with encystation-specific vesicles. Besides the endomembrane system, the presence of GlBet3 and GlBet5 at the plasma membrane, membrane wrapping ventral disc periphery, and the median body indicates that the TRAPP complex may support unique features and functions of Giardia.