Evolutionary emergence of N-glycosylation as a variable promoter of HCN channel surface expression.
All four mammalian hyperpolarization-activated cyclic nucleotide-modulated (HCN) channel isoforms have been shown to undergo N-linked glycosylation in the brain. With the mouse HCN2 isoform as a prototype, HCN channels have further been suggested to require N-glycosylation for function, a provocative finding that would make them unique in the voltage-gated potassium channel superfamily. Here, we show that both the HCN1 and HCN2 isoforms are also predominantly N-glycosylated in the embryonic heart, where they are found in significant amounts and where HCN-mediated currents are known to regulate beating frequency. Surprisingly, we find that N-glycosylation is not required for HCN2 function, although its cell surface expression is highly dependent on the presence of N-glycans. Comparatively, disruption of N-glycosylation only modestly impacts cell surface expression of HCN1 and leaves permeation and gating functions almost unchanged. This difference between HCN1 and HCN2 is consistent with evolutionary trajectories that diverged in an isoform-specific manner after gene duplication from a common HCN ancestor that lacked N-glycosylation and was able to localize efficiently to the cell surface.
Department of Cellular and Physiological Sciences, University of British Columbia, Vancouver, Canada.
Andrew P
AP
Hegle
Hamed
H
Nazzari
Andrew
A
Roth
Damiano
D
Angoli
Eric A
EA
Accili
D000595:Amino Acid Sequence; D019943:Amino Acid Substitution; D000818:Animals; D016466:CHO Cells; D002462:Cell Membrane / Q000378:metabolism*; D006224:Cricetinae; D003412:Cricetulus; D054815:Cyclic Nucleotide-Gated Cation Channels / Q000235:genetics* / Q000378:metabolism*; D004622:Embryo, Mammalian / Q000378:metabolism; D019143:Evolution, Molecular; D005786:Gene Expression Regulation; D006031:Glycosylation; D006321:Heart / Q000196:embryology; D064428:Hyperpolarization-Activated Cyclic Nucleotide-Gated Channels; D007473:Ion Channels / Q000235:genetics / Q000378:metabolism*; D051379:Mice; D008969:Molecular Sequence Data; D009206:Myocardium / Q000378:metabolism; D010802:Phylogeny; D015221:Potassium Channels / Q000235:genetics* / Q000378:metabolism*; D051381:Rats
D054815:Cyclic Nucleotide-Gated Cation Channels; C578666:Hcn1 protein, mouse; C578667:Hcn1 protein, rat; C578711:Hcn2 protein, mouse; C578712:Hcn2 protein, rat; D064428:Hyperpolarization-Activated Cyclic Nucleotide-Gated Channels; D007473:Ion Channels; D015221:Potassium Channels