Stoichiometry of recombinant heteromeric glycine receptors revealed by a pore-lining region point mutation.

Heteromeric glycine receptors mediate synaptic inhibition in the caudal areas of the adult mammalian central nervous system (CNS). These channels resemble other receptors in the nicotinic superfamily in that they are pentamers, but may differ in that they contain α and β subunits in a 3:2 rather than a 2:3 ratio. Evidence in favor of a 3α:2β stoichiometry of heteromeric glycine receptors comes from biochemical data and from the expression of chimeric subunits. We investigated this question using a potentially more direct approach and mutated the highly conserved hydrophobic residues in the middle (position 9′) of the pore-lining domain. This mutation increases agonist potency in all channels in the nicotinic superfamily and its effects are in first approximation proportional to the number of mutant subunit incorporated into the receptor. We expressed in HEK 293 cells wild-type glycine α1β receptors or receptors bearing the 9′ mutation on either the α or the β subunit, using an α:β plasmid ratio of 1:40 in...