Assembly of the inhibitory glycine receptor: Identification of amino acid sequence motifs governing subunit stoichiometry

Abstract

The inhibitory glycine receptor (GlyR) is a pentameric protein composed of two types (α and β) of membrane-spanning subunits. Coexpression in Xenopus oocytes of a low affinity mutant of the α2 subunit with the α1 and β subunits indicated that GlyRs assembled from α1 and α2 polypeptides contain variable subunit ratios, whereas $\text{α}\text{β}$ hetero-oligomers have an invariant (3:2) stoichiometry. Analysis of different $\text{α}\text{β}$ chimeric constructs revealed that this difference in assembly behavior is mediated by the N-terminal extracellular regions of the receptor subunits. Substitution of residues diverging between the α and β subunits identified combinations of sequence motifs determining subunit stoichiometry.