INIMEC - CONICET   05467
INSTITUTO DE INVESTIGACION MEDICA MERCEDES Y MARTIN FERREYRA
Unidad Ejecutora - UE
congresos y reuniones científicas
Título:
Giardia Lipoprotein Receptor-related Protein: a novel LDRP member family in a primitive eukaryotic cell.
Autor/es:
RIVERO MR; ROPOLO ANDREA; TOUZ MC
Lugar:
Armação dos Búzios, RJ, Brasil
Reunión:
Congreso; . XIII International Congress of Protistology; 2009
Resumen:
The LDLR is the founding member of a family of seven structurally related transmembrane proteins (Lipoprotein Receptor-related Protein 1 –LRP-1, 1b, megalin/LRP2, LDL receptor, very low-density lipoprotein receptor, MEGF7/LRP4, LRP8/apolipoprotein E receptor2). In a GGD survey, we identified a protein that shares a cysteine-rich N-terminal domain with LRP1 and LRP1b and named gLRP for Giardia Lipoprotein Receptor-related Protein. This is a 116 kDa predicted type I membrane protein that possesses a signal peptide, a 20 aa transmembrane domain (from aa 1009 to 1029), and a cytoplasmic tail of 41 aa at the C-terminus. Interestingly, the cysteine-rich domain has been shown to be important for LDL binding and LDL internalization by endocytosis. Using confocal microscopy, we determined that the HA-tagged gLRP colocalized with LDL at the plasma membrane and in the lysosome-like peripheral vacuoles (PVs). Surface localization of gLRP was confirmed using TIRFM. Furthermore, epifluorescence microscopy demonstrated that gLRP was also present in the nuclei. The nuclear localization of gLRP implies the participation of this receptor in cell signaling, as has been extensively described for the LRP family. In addition, similar to LRP1 and LRP1b, gLRP contains a potential FXNPXY-type internalization signal (FNSPTY) within its cytoplasmic tail. By YTH and co-IPP assays, we found that gLRP directly bind to the medium subunit of Giardia adaptor protein 2. Because no LRP-like adaptor proteins that contain a PTB domain, such as ARH or Dab, have been found in Giardia, we hypothesized that gAP2 alone has the ability to direct gLRP to the PVs. These results suggest that gLRP is involved in the internalization of cholesterol from LDL via a regulated AP2-clathrin-dependent pathway. We can conclude that the delivery of specific proteins to the lysosome occurs in this parasite, with the peculiarity that the machinery involved in the process seems to be very simple. Supported by R01 TW007245, NIH (USA), PIP6563, CONICET (Argentina), and PICT20221, FONCyT (Argentina).