N-glycosylation sites on the nicotinic ACh receptor subunits regulate receptor channel desensitization and conductance.
The present study investigated the effects of N-glycosylation sites on Torpedo acetylcholine (ACh) receptors expressed in Xenopus oocytes by monitoring whole-cell membrane currents and single-channel currents from excised patches. Receptors with the mutant subunit at the asparagine residue on the conserved N-glycosylation site (mbetaN141D, mgammaN141D, or mdeltaN143D) or the serine/threonine residue (mbetaT143A, mgammaS143A, or mdeltaS145A) delayed the rate of current decay as compared with wild-type receptors, and the most striking effect was found with receptors with mbetaT143A or mgammaS143A. For wild-type receptors, the lectin concanavalin A, that binds to glycosylated membrane proteins with high affinity, mimicked this effect. Receptors with mbetaN141D or mdeltaN143D exhibited lower single-channel conductance, but those with mbetaT143A, mgammaS143A, or mdeltaS145A otherwise revealed higher conductance than wild-type receptors. Mean opening time of single-channel currents was little affected by the mutation. N-glycosylation sites, thus, appear to play a role in the regulation of ACh receptor desensitization and ion permeability.
Nishizaki
Tomoyuki
T
Department of Physiology, Hyogo College of Medicine, 1-1 Mukogawa-cho, Nishinomiya 663-8501, Japan. tomoyuki@hyo-med.ac.jp
D000818:Animals; D001665:Binding Sites / Q000235:genetics; D002462:Cell Membrane / Q000378:metabolism*; D005260:Female; D006031:Glycosylation; D007473:Ion Channels / Q000235:genetics / Q000378:metabolism*; D008564:Membrane Potentials / Q000235:genetics; D009154:Mutation / Q000235:genetics; D009865:Oocytes; D021122:Protein Subunits / Q000235:genetics*; D011952:Receptors, Concanavalin A / Q000235:genetics; D011978:Receptors, Nicotinic / Q000235:genetics / Q000378:metabolism*; D009435:Synaptic Transmission / Q000235:genetics; D014101:Torpedo; D014981:Xenopus
D007473:Ion Channels; D021122:Protein Subunits; D011952:Receptors, Concanavalin A; D011978:Receptors, Nicotinic