Structural basis for ?-bungarotoxin insensitivity of neuronal nicotinic acetylcholine receptors.

ABSTRACT: The ten types of nicotinic acetylcholine receptor ?-subunits show substantial sequence homology, yet some types confer high affinity for ?-bungarotoxin, whereas others confer negligible affinity. Combining sequence alignments with structural data reveals three residues unique to ?-toxin-refractory ?-subunits that coalesce within the 3D structure of the ?4?2 receptor and are predicted to fit between loops I and II of ?-bungarotoxin. Mutating any one of these residues, Lys189, Ile196 or Lys153, to the ?-toxin-permissive counterpart fails to confer ?-bungarotoxin binding. However, mutating both Lys189 and Ile196 affords ?-bungarotoxin binding with an apparent dissociation constant of 104?nM, while combining mutation of Lys153 reduces the dissociation constant to 22?nM. Analogous residue substitutions also confer high affinity ?-bungarotoxin binding upon ?-toxin-refractory ?2 and ?3 subunits. ?4?2 receptors engineered to bind ?-bungarotoxin exhibit slow rates of ?-toxin association and dissociation, and competition by cholinergic ligands typical of muscle nicotinic receptors. Receptors engineered to bind ?-bungarotoxin co-sediment with muscle nicotinic receptors on sucrose gradients, and mirror single channel signatures of their ?-toxin-refractory counterparts. Thus the inability of ?-bungarotoxin to bind to neuronal nicotinic receptors arises from three unique and interdependent residues that coalesce within the receptor's 3D structure.

SUBMITTER: Sine SM 

PROVIDER: S-EPMC6842095 | biostudies-literature | 2019 Dec

REPOSITORIES: biostudies-literature