Role of Adaptin Complexes in Protein Trafficking to Lysosome-like Vacuoles in Giardia lamblia.

MARIA CAROLINA TOUZ

Huerta Grande. Cordoba

Simposio; XXI Reunión Anual de la Sociedad Argentina de Parasitología.; 2006

SAP

  Giardia lamblia is an earlier branching protist that possesses a unique secretory system. In mammalian cells, lysosomal trafficking is achieved by adaptor proteins or adaptins (APs) that recognize specific sequences (tyrosine and/or dileucine motifs) in the cytoplasmic tail of membrane proteins. We found that Giardia has a tyrosine-based sorting system, which mediates the targeting of a cysteine protease to the endosome/lysosome-like peripheral vacuoles (PVs) in a clathrin-adaptin dependent process. We also found that the delivery of the soluble lysosomal hydrolases to the PVs is AP1 dependent. Nevertheless, the nature of the hydrolases receptor remains elusive. Even though Giardia trophozoites lack a morphologically discernible Golgi apparatus, the presence of a clathrin-adaptor system suggests that this parasite may possess a primitive secretory organelle capable of sorting proteins similar to that of more evolved cells. The presence of the two large, one medium, and one small subunit of AP2 homologous proteins in the Giardia genome database supports the hypothesis that Giardia possesses a similar mechanism where receptor-specific transport of molecules from the parasite surface to the PVs involves AP2. There is no evidence that other adaptor proteins are implicated. Further studies regarding additional molecules involved in lysosomal sorting in Giardia will provide new insight into the minimal machinery necessary for intracellular transport in higher eukaryotes.