Secretory granule biogenesis and release in the early-branching eukaryote Giardia lamblia

NATALIA GOTTIG; MARIA JIMENA NORES; VANINA ELÍAS; ALBERTO SOLARI; MARIA CAROLINA TOUZ; HUGO DANIEL LUJAN

Carlos Paz - Córdoba

Workshop; International Worshop on Membrane trafficking; 2005

Giardia is an intestinal parasitic protozoan of humans.Trophozoites undergo fundamental changes to survive outside the intestine by differentiating into cysts.Encystation entails the synthesis, processing, transport, secretion and assembly of cyst wall componenets.Among those molecules are three closely related cyst wall proteins (CWPs) that localize within encystation-specific secretory vesicles (ESVs) in encysting trophozoites and in the cyst wall madure cysts.The CWP genes predict of 26 (CWP1), 39 (CWP2), and 27 (CWP3) kDa, having 61% identity in 26 kDa overlapping region. CWP2 differs from CWP1 and CWP3 by a 121-residue carboxy-terminal extension rich in basic amino acid. We demostrated that this domain is cleaved before cyst wall assembly by a cysteine protease induced during encystation . In this work we determined the role of the alkaline extension of CWP2 and identified and characterized SNARE proteins involved in Giardia encystation.Our results indicate that the CWP2 basic extension is necessary for sorting CWPs To ESVs but its presence is not sufficient to induce secretory granule biogenesis in non-encysting trophozoites and that other regions of CWPs are required for aggregation and de ESV formation.In addition, by expression of HA-tagged molecules, antisense silencing, and yeast two-hybrid analysis of Giardia SNAREs, we found that seven of these proteins localize to specific subcellular compartments, are essential for parasite viability, and show specific SNARE-SNARE interaction.These results provide new insights into the miniomal machinery for protein trafficking utilized by Giardia during differentiation into cyst.