Abstract
Traffic of integral membrane proteins along the secretory pathway is not simply a default process but can be selective. Such selectivity is achieved by sequence information within the cargo protein that recruits coat protein complexes to drive the formation of transport vesicles. A number of sequence motifs have been identified in the cytoplasmic domains of ion channels that regulate early trafficking events between the endoplasmic reticulum and the Golgi complex. Here, we demonstrate that the following trafficking step from the Golgi compartment to the plasma membrane can also be selective. The N-terminal domain of the inward rectifier potassium channel Kir2.1 contains specific sequence information that is necessary for its efficient export from the Golgi complex. Lack of this information results in accumulation of the protein within the Golgi and a significant decrease in cell surface expression. As similar results were obtained for the N terminus of another Kir channel subfamily member, Kir4.1, which could functionally substitute for the Kir2.1 N terminus, we propose a more general role of the identified N-terminal domains for post-Golgi trafficking of Kir channels.
Highlights
Ion channels are sorted via the secretory pathway
As similar results were obtained for the N terminus of another Kir channel subfamily member, Kir4.1, which could functionally substitute for the Kir2.1 N terminus, we propose a more general role of the identified N-terminal domains for post-Golgi trafficking of Kir channels
The channel protein accumulated in a juxtanuclear compartment that we identified as the Golgi complex by the following. (i) Incubation of transfected cells with the fungal Golgi toxin brefeldin A (BFA) led to a reversible redistribution of GFPKir2.1⌬1–76 to the endoplasmic reticulum (ER); and (ii) we found colocalization of GFPKir2.1⌬1–76 with the red fluorescent protein DsRed fused to the targeting sequence of the Golgi-resident enzyme galactosyltransferase I [25] (Fig. 1C)
Summary
Ion channels are sorted via the secretory pathway. After synthesis in the endoplasmic reticulum (ER),1 they are forwarded to the Golgi complex from which they are transported to the plasma membrane. The N-terminal domain of the inward rectifier potassium channel Kir2.1 contains specific sequence information that is necessary for its efficient export from the Golgi complex. Whereas its C terminus bears a previously identified ER export motif [16, 17], sequence information contained in its N terminus is necessary for post-Golgi trafficking to the plasma membrane.
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