Identification and characterization of site-specific N-glycosylation in the potassium channel Kv3.1b

The potassium ion channel Kv3.1b is a member of a family of voltage-gated ion channels that are glycosylated in their mature form. In the present study, we demonstrate the impact of N-glycosylation at specific asparagine residues on the trafficking of the Kv3.1b protein. Large quantities of asparagine 229 (N229)-glycosylated Kv3.1b reached the plasma membrane, whereas N220-glycosylated and unglycosylated Kv3.1b were mainly retained in the endoplasmic reticulum (ER). These ER-retained Kv3.1b proteins were susceptible to degradation, when co-expressed with calnexin, whereas Kv3.1b pools located at the plasma membrane were resistant. Mass spectrometry analysis revealed a complex type Hex₃HexNAc₄Fuc₁ glycan as the major glycan component of the N229-glycosylated Kv3.1b protein, as opposed to a high-mannose type Man₈GlcNAc₂ glycan for N220-glycosylated Kv3.1b. Taken together, these results suggest that trafficking-dependent roles of the Kv3.1b potassium channel are dependent on N229 site-specific glycosylation and N-glycan structure, and operate through a mechanism whereby specific N-glycan structures regulate cell surface expression.