Title : N-glycosylation promotes the cell surface expression of Kv1.3 potassium
channels
Abstract :
- The voltage-gated potassium channel Kv1.3 plays an essential role in modulating membrane excitability in many cell types
- Kv1.3 is a heavily glycosylated membrane protein
- Two successive N-glycosylation consensus sites , N228NS and N229ST, are present on the S1-S2 linker of rat Kv1.3
- Our data suggest that Kv1.3 contains only one N-glycan and it is predominantly attached to N229 in the S1-S2 extracellular linker
- Preventing N-glycosylation of Kv1.3 significantly decreased its surface protein level and surface conductance density level, which were ∼ 49% and ∼ 46% respectively of the level of wild type
- Supplementation of N-acetylglucosamine (GlcNAc), l-fucose or N-acetylneuraminic acid to the culture medium promoted Kv1.3 surface protein expression, whereas supplementation of d-glucose, d-mannose or d-galactose did not
- Among the three effective monosaccharides/derivatives, adding GlcNAc appeared to reduce sialic acid content and increase the degree of branching in the N-glycan of Kv1.3, suggesting that the N-glycan structure and com position had changed
- Furthermore, the cell surface half-life of the Kv1.3 surface protein was increased upon GlcNAc supplementation, indicating that it had decreased internalization
- The GlcNAc effect appears to apply mainly to membrane proteins containing complex type N-glycans
- Thus, N-glycosylation promotes Kv1.3 cell surface expression; supplementation of GlcNAc increased Kv1.3 surface protein level and decreased its internalization, presumably by a combined effect of decreased branch size and increased branching of the N-glycan