Characterization of SNAREs determines the absence of a typical Golgi apparatus in the ancient eukaryote Giardia lamblia

ELIAS EV; QUIROGA R; GOTTIG N; NAKANISHI H; NASH TE; NEIMAN A; LUJAN HD

JOURNAL OF BIOLOGICAL CHEMISTRY

American Society of Biochemistry and Molecular Biology, Inc.

Lugar: Bethesda, Maryland, USA; Año: 2008 vol. 283 p. 35996 - 36010

0021-9258

Giardia is an eukaryotic protozoal parasite with unusual characteristics, such as the absence of a morphologically evident Golgi apparatus. Although both constitutive and regulated pathways for protein secretion are evident in Giardia, little is known about the mechanisms involved in vesicular docking and fusion. In higher eukaryotes, soluble Nethylmaleimide- sensitive factor-attachment protein receptors (SNAREs) of the vesicleassociated membrane protein (VAMP) and Syntaxin families play essential roles in these processes. In this work we identified and characterized genes for seventeen SNAREs in Giardia to define the minimal set of subcellular organelles present during growth and encystation, in particular the presence or not of a Golgi apparatus. Expression and localization of all Giardia SNAREs demonstrate their presence in distinct subcellular compartments, which may represent the extent of the endomembrane system in eukaryotes. Remarkably, Giardia SNAREs homologous to Golgi SNAREs from other organisms does not allow the detection of a typical Golgi apparatus in either proliferating or differentiating trophozoites. However, some features of the Golgi, such us packaging and sorting function, seem to be performed by the ER and/or the nuclear envelope. Moreover, depletion of individual genes demonstrated that several SNAREs are essential for viability, while others are dispensable. Thus, Giardia requires a smaller number of SNAREs, compared to other eukaryotes, to accomplish all the vesicle trafficking events that are critical for growth and differentiation of this important human pathogen.