title: Differential effects of N-glycans on surface expression suggest structural differences between the acid-sensing ion channel (ASIC) 1a and ASIC1b.
abstract: ASICs (acid-sensing ion channels) are H(+)-gated Na(+) channels with a widespread expression pattern in the central and the peripheral nervous system. ASICs have a simple topology with two transmembrane domains, cytoplasmic termini and a large ectodomain between the transmembrane domains; this topology has been confirmed by the crystal structure of chicken ASIC1. ASIC1a and ASIC1b are two variants encoded by the asic1 gene. The variable part of the protein includes the cytoplasmic N-terminus, the first transmembrane domain and approximately the first third of the ectodomain. Both variants contain two consensus sequences for N-linked glycosylation in the common, distal part of the ectodomain. In contrast with ASIC1a, ASIC1b contains two additional consensus sequences in the variable, proximal part of the ectodomain. Here we show that all the extracellular asparagine residues within the putative consensus sequences for N-glycosylation carry glycans. The two common distal glycans increase surface expression of the channels, but are no absolute requirement for channel activity. In sharp contrast, the presence of at least one of the two proximal glycans, which are specific to ASIC1b, is an absolute requirement for surface expression of ASIC1b. This result suggests substantial differences in the structure of the proximal ectodomain between the two ASIC1 variants.
authors.affiliation: Institute of Physiology II, University of Würzburg, Röntgenring 9, D-97070 Würzburg, Germany.
authors.forename: Ivan
authors.initials: I
authors.lastname: Kadurin
authors.forename: Andjelko
authors.initials: A
authors.lastname: Golubovic
authors.forename: Lilia
authors.initials: L
authors.lastname: Leisle
authors.forename: Hermann
authors.initials: H
authors.lastname: Schindelin
authors.forename: Stefan
authors.initials: S
authors.lastname: Gründer
mesh_terms: D062565:Acid Sensing Ion Channels; D000818:Animals; D002462:Cell Membrane / Q000378:metabolism; D004594:Electrophysiology; D006031:Glycosylation; D008564:Membrane Potentials; D008958:Models, Molecular; D016297:Mutagenesis, Site-Directed; D009419:Nerve Tissue Proteins / Q000737:chemistry* / Q000378:metabolism*; D011134:Polysaccharides / Q000378:metabolism*; D011487:Protein Conformation; D051381:Rats; D015222:Sodium Channels / Q000737:chemistry* / Q000378:metabolism*; D014982:Xenopus laevis
chemical_list: D062565:Acid Sensing Ion Channels; C568268:Asic1 protein, rat; D009419:Nerve Tissue Proteins; D011134:Polysaccharides; D015222:Sodium Channels