Role of C-terminus of Kir7.1 potassium channel in cell-surface expression

Inward rectifier K+ channel Kir7.1 is predominantly expressed on the plasma membrane of a variety of ion-transporting epithelia. The electrophysiological property of Kir7.1 has been well characterized but the mechanism underlying the plasma-membrane targeting remains elusive. To address this issue, we examined the effect of deletion and site-directed mutagenesis on the plasma-membrane localization of Kir7.1 in Madin-Darby canine kidney cells by immunofluorescence microscopy and cell-surface biotinylation. Although deletions of up to 37 amino acid residues from the C-terminus had no effect, further deletion resulted in accumulation of the mutant proteins in intracellular membranes. No sequence motif for subcellular targeting was found in the distal C-terminal region. The cell-surface expression of the deletion mutant lacking 38 or 40 C-terminal residues was restored by addition of one or three alanine residues, respectively, to the C-terminus end. These results suggest that the C-terminal length plays an important role in the plasma-membrane localization of Kir7.1.