Protein Transport to Lysosome in Eukaryotes: A Simplified Model in the Protozoa Giardia lamblia.

RIVERO MR; MARIA CAROLINA TOUZ; LUJAN HD

Rosario

Congreso; 42nd Annual Meeting. Argentine Society for Biochemistry and Molecular Biology Research.; 2006

SAIB

Giardia lamblia is an earlier branching protist that possesses a unique secretory system. This parasite lacks compartments that resemble early/late endosomes and lysosomes; instead, it possesses peripheral vacuoles (PVs) that seem to function as endosomes and lysosomes at the same time. The long-term goal of this work is to determine the molecular mechanisms involved in intracellular protein trafficking from and to the PVs in this organism. Lysosomal trafficking is achieved by adaptins (APs) that recognize specific tyrosine-based motifs in the cytoplasmic tail of membrane proteins. We found that Giardia has a tyrosine-based sorting system, which mediates the targeting of membrane and soluble lysosomal hydrolases to the PVs in a clathrin-adaptin dependent manner. Nevertheless, the nature of the hydrolases receptor remains elusive. Here, by using pull-down assays, we show that a putative hydrolase receptor (gHR) interacts with the soluble acid phosphatase and possesses a similar localization pattern. It also contains a tyrosine-based motif that could be recognized by AP1. On the other hand, we show that gAP2 is likely involved in receptor-mediated endocytosis by using a knock-down strategy and uptake experiments. Further studies will provide new insight into the minimal machinery necessary for intracellular transport in higher eukaryotes.