Title : Topological analysis of
Niemann-Pick C1 protein reveals that the membrane orientation of the putative sterol-sensing
domain is identical to those of 3-hydroxy-3-methylglutaryl-CoA
reductase and
sterol regulatory element binding protein cleavage-activating protein
Abstract :
- The Niemann-Pick C1 ( NPC1 ) protein is predicted to be a polytopic glycoprotein , and it contains a region with extensive homology to the sterol-sensing domains (SSD) of 3-hydroxy-3-methylglutaryl-coenzyme A reductase ( HMG-R ) and sterol regulatory element binding protein cleavage-activating protein ( SCAP )
- To aid the functional characterization of NPC1 , a model of NPC1 topology was evaluated by expression of epitope-tagged NPC1 proteins and investigation of epitope accessibility in selectively permeabilized cells
- These results were further confirmed by expression of NPC1 and identification of glycosylated domains that are located in the lumen of the endoplasmic reticulum
- Our data indicate that this glycoprotein contains 13 transmembrane domains , 3 large and 4 small luminal loops, 6 small cytoplasmic loops, and a cytoplasmic tail
- Furthermore, our data show that the putative SSD of NPC1 is oriented in the same manner as those of HMG-R and SCAP , providing strong evidence that this domain is functionally important