Giardia lamblia: An unique model of protein transport to lysosome in eukaryotes.

RIVERO MR; CONRAD JT; LUJAN HD; NASH TE; MARIA CAROLINA TOUZ

Mendoza. Argentina

Congreso; VII Congreso Argentino de Protozoología y Enfermedades Parasitarias. SAP 2005.; 2005

Giardia lamblia is a primitive eukaryotic cell that possesses a unique secretory system. In mammalian cells, lysosomal trafficking is achieved by adaptor proteins (APs) that recognize specific sequences (tyrosine and/or dileucine motifs) in the cytoplasmic tail of membrane proteins. We previously demonstrated that Giardia has a tyrosine-based sorting system, which mediates the targeting of an cysteine protease to the endosome/lysosome-like peripheral vacuoles (PVs) in a clathrin-adaptin dependent process. We now show that receptor-specific transport of molecules from the parasite surface to the PVs involves AP2. By tetracycline-induced expression of the medium subunit (µ) of AP2 and immunofluorescence assays we were able to localize Giardia AP2 in small vesicles close to the plasma membrane. A µ2 antisense strategy and uptake experiments using FITC labeled dextran and LDL suggest that AP2 is involved in receptor-mediated endocytosis. On the other hand, we recently reported that also the delivering of the soluble lysosomal hydrolase acid phosphatase (AcPh) to the PVs is AP1 dependent. Nevertheless, the nature of the receptor that sorts AcPh to de PVs remains elusive. By pull-down assays using a His-tagged AcPh we were able to purify the recombinant enzyme together with associated proteins. Analysis of these sequences by mass spectrometry showed that molecules that potentially interact with AcPh in vivo are homologues to proteins involved in lysosomal transport in higher cells, indicatting that Giardia possesses a mechanism of protein delivery to lysosomes similar to more evolved cells. 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.