N-linked glycosylation of Kv1.2 voltage-gated potassium channel facilitates cell surface expression and enhances the stability of internalized channels.

Abstract

Kv1.2 and related voltage-gated potassium channels have a highly conserved N-linked glycosylation site in the first extracellular loop, with complex glycosylation in COS-7 cells similar to endogenous Kv1.2 glycosylation in hippocampal neurons. COS-7 cells expressing Kv1.2 show a crucial role of this N-linked glycosylation in the forward trafficking of Kv1.2 to the cell membrane. Although both wild-type and non-glycosylated mutant Kv1.2 channels that have reached the cell membrane are internalized at a comparable rate, mutant channels are degraded at a faster rate. Treatment of wild-type Kv1.2 channels on the cell surface with glycosidase to remove sialic acids also results in the faster degradation of internalized channels. Glycosylation of Kv1.2 is important with respect to facilitating trafficking to the cell membrane and enhancing the stability of channels that have reached the cell membrane. Studies in cultured hippocampal neurons and the COS-7 cell line demonstrate important roles for N-linked glycosylation of Kv1.2 channels in forward trafficking and protein degradation. Kv1.2 channels can contain complex N-linked glycans, which facilitate cell surface expression of the channels. Additionally, the protein stability of cell surface-expressed Kv1.2 channels is affected by glycosylation via differences in the degradation of internalized channels. The present study reveals the importance of N-linked complex glycosylation in boosting Kv1.2 channel density. Notably, sialic acids at the terminal sugar branches play an important role in dampening the degradation of Kv1.2 internalized from the cell membrane to promote its stability.