Open AccessAn Extracellular Loop of the Human Non-Gastric H,K-ATPase a-subunit is Involved in Apical Plasma Membrane Polarization
Author(s) -
Markus Lerner,
Dieter Lemke,
H. P. Bertram,
Hermann Schillers,
Hans Oberleithner,
Michael J. Caplan,
Jürgen Reinhardt
Publication year - 2006
Publication title -
cellular physiology and biochemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.486
H-Index - 87
eISSN - 1421-9778
pISSN - 1015-8987
DOI - 10.1159/000095169
Subject(s) - apical membrane , microbiology and biotechnology , epithelial polarity , transfection , extracellular , biology , cell polarity , atpase , protein subunit , chemistry , transmembrane protein , biochemistry , membrane , cell , receptor , enzyme , gene
The human non-gastric H,K-ATPase, ATP1AL1, belongs to the gene family of P-type ATPases. Consistent with their physiological roles in ion transport, members of this group, including the Na,KATPase and the gastric and non-gastric H,K-ATPases, are differentially polarized to either the basolateral or apical plasma membrane in epithelial cells. However, their polarized distribution is highly complex and depends on specific sorting signals or motifs which are recognized by the subcellular targeting machinery. For the gastric H,K-ATPase it has been suggested that the 4(th) transmembrane spanning domain (TM4) and its flanking regions induce conformational sorting motifs which direct the ion pump exclusively to the epithelial apical membrane. Here, we show in transfected Madin-Darby canine kidney (MDCK) cells that the related non-gastric H,KATPase, ATP1AL1, does contain similar sorting motifs in close proximity to TM4. A short extracellular loop between TM3 and TM4 is critical for this pump's apical delivery. A single point mutation in the corresponding region redirects ATP1AL1 to the basolateral membrane. In conclusion, our work provides further evidence that the cellular distribution of P-type ATPases is determined by conformational sorting motifs.