Evidence for an apical sorting signal on the ectodomain of human aminopeptidase N.
In polarized epithelial cells aminopeptidase N is targeted to the apical membrane. The aim of this study was to determine whether a sorting signal is necessary for its correct transport to the apical membrane and, if so, to localize this sorting signal to one of the domains of the transmembrane protein. Anchor-minus aminopeptidase N, consisting of the hemagglutinin signal peptide including its cleavage site, and the ectoplasmic domain of human aminopeptidase N were stably expressed in Madin-Darby canine kidney cells cultured on polycarbonate filters. By measurement of the enzymatic activity it was found that the anchor-minus aminopeptidase N was secreted in a polarized manner to the apical side. As a reference the secretion of the secretory granule protein, cystatin C, was likewise studied. Cystatin C was found to be secreted in a nonpolarized manner to both domains. Our data thus show that human aminopeptidase N carries an apical sorting signal and that it is localized on the ectodomain of the enzyme.
Department of Biochemistry C, Panum Institute, University of Copenhagen, Denmark.
L K
LK
Vogel
M
M
Spiess
H
H
Sjöström
O
O
Norén
D000595:Amino Acid Sequence; D000626:Aminopeptidases / Q000235:genetics / Q000378:metabolism*; D000818:Animals; D001692:Biological Transport; D015153:Blotting, Western; D018826:CD13 Antigens; D002462:Cell Membrane / Q000201:enzymology; D002478:Cells, Cultured; D004285:Dogs; D004591:Electrophoresis, Polyacrylamide Gel; D006801:Humans; D007668:Kidney / Q000166:cytology / Q000201:enzymology; D008969:Molecular Sequence Data; D010957:Plasmids; D021382:Protein Sorting Signals / Q000378:metabolism*
D021382:Protein Sorting Signals; D000626:Aminopeptidases; D018826:CD13 Antigens