Stoichiometry of the Human Glycine Receptor Revealed by Direct Subunit Counting

The subunit stoichiometry of heteromeric glycine-gated channels determines fundamental properties of these key inhibitory neurotransmitter receptors; however, the ratio of alpha 1- to beta-subunits per receptor remains controversial. We used single-molecule imaging and stepwise photobleaching in Xenopus oocytes to directly determine the subunit stoichiometry of a glycine receptor to be 3 alpha 1:2 beta. This approach allowed us to determine the receptor stoichiometry in mixed populations consisting of both heteromeric and homomeric channels, additionally revealing the quantitative proportions for the two populations.