N-glycosylation sites on the nicotinic ACh receptor subunits regulate receptor channel desensitization and conductance

Abstract

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 (mβN141D, mγN141D, or mδN143D) or the serine/threonine residue (mβT143A, mγS143A, or mδS145A) delayed the rate of current decay as compared with wild-type receptors, and the most striking effect was found with receptors with mβT143A or mγS143A. For wild-type receptors, the lectin concanavalin A, that binds to glycosylated membrane proteins with high affinity, mimicked this effect. Receptors with mβN141D or mδN143D exhibited lower single-channel conductance, but those with mβT143A, mγS143A, or mδS145A 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.