title: The degree of N-glycosylation affects the trafficking and cell surface expression levels of Kv1.4 potassium channels.
abstract: Kv1.4 potassium channels are heavily glycosylated proteins involved in shaping action potentials and in neuronal excitability and plasticity. Kv1.4 N354Q, without an N-glycan, exhibited decreased protein stability and trafficking to the cell surface (Watanabe et al. in J Biol Chem 279:8879-8885, 2004). Here we investigated whether the composition of the N-glycan affected Kv1.4 cell surface expression. Kv1.4 proteins carrying N-glycans with different compositions were generated by adding glycosidase inhibitors or using N-glycosylation-deficient mutant cell lines. We found that oligomannose-type, hybrid-type, or incomplete complex-type N-glycans had a negative effect on surface protein expression of Kv1.4 compared with complex-type N-glycans. The decrease in surface protein level of Kv1.4 was mainly due to a reduction in total protein level, induced by altered N-glycan composition. Kv1.4 in CSTP-treated cells carried a unique oligomannose-type N-glycan that contains three glucose residues. This N-glycan had the most negative effect on cell surface expression of Kv1.4. It decreased Kv1.4 surface protein level by a combined mechanism of reducing total protein level and increasing ER-retention. Our data suggest that composition of the N-glycan plays an important role in protein stability and trafficking, and a sialylated complex-type N-glycan promoted high cell surface expression of Kv1.4.
authors.affiliation: Department of Biological Sciences and Center for Cancer, Genetic Diseases and Gene Regulation, Fordham University, Bronx, NY, 10458, USA.
authors.forename: Itaru
authors.initials: I
authors.lastname: Watanabe
authors.forename: Jing
authors.initials: J
authors.lastname: Zhu
authors.forename: Esperanza
authors.initials: E
authors.lastname: Recio-Pinto
authors.forename: William B
authors.initials: WB
authors.lastname: Thornhill
mesh_terms: D000818:Animals; D016466:CHO Cells; D002462:Cell Membrane / Q000378:metabolism*; D003412:Cricetulus; D004721:Endoplasmic Reticulum / Q000378:metabolism; D004791:Enzyme Inhibitors / Q000494:pharmacology; D015870:Gene Expression; D006026:Glycoside Hydrolases / Q000037:antagonists & inhibitors; D006031:Glycosylation / Q000187:drug effects; D051665:Kv1.4 Potassium Channel / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D008358:Mannose / Q000737:chemistry / Q000378:metabolism; D009154:Mutation; D011134:Polysaccharides / Q000737:chemistry / Q000378:metabolism; D017510:Protein Folding; D055503:Protein Multimerization; D021381:Protein Transport
chemical_list: D004791:Enzyme Inhibitors; D051665:Kv1.4 Potassium Channel; D011134:Polysaccharides; D006026:Glycoside Hydrolases; D008358:Mannose