Identification, cloning and functional characterization of a novel Giardia LRP-like protein

RIVERO M.R.; MIRAS S.L.; QUIROGA R.; ZAMPONI N.; FELIZIANI C. ; ROPOLO A.S.; TOUZ M.C.

Congreso; XLVI Reunión Anual de la Sociedad Argentina de Investigación en Bioquímica y Biología Molecular; 2010

As Giardia lamblia is unable to synthesize cholesterol de novo, this compound might be obtained from the intestinal milieu by endocytosis of lipoproteins. Here, we identified a putative Giardia LRP (GlLRP), a type-I membrane protein, which shares the substrate-N-terminal binding domain and a FXNPXY-type endocytic motif with the human Low-density lipoprotein Receptor related Proteins (LRPs). Expression of tagged-GlLRP showed that it was localized in the ER, lysosomal-like peripheral vacuoles, PM and nuclei. However, the FXNPXY-deleted GlLRP was retained at the PM suggesting that it is abnormally transported and processed. LDL and chylomicrons interacted with GlLRP, with this interaction being necessary for lipoprotein internalization. GlLRP was found to bind directly to the medium subunit of Giardia adaptor protein 2(AP2), indicating that receptor mediated internalization occurs through an adaptin mechanism. Beside, by an antisense strategy we showed that GlLRP plays a pivotal role in parasite replication. Finally, we showed that the degradation of GlLRP was in part due to the action of a ã-secretase-like complex, which had a significant effect in its nuclear localization. We postulate that GlLRP is involved in the internalization of cholesterol from lipoproteins via a regulated AP2-dependent pathway and possesses a potential role in the intracellular signaling.